Developing user-defined extensions (UDxs)

• 1: Developing with the Vertica SDK
• 1.1: Setting up a development environment
• 1.2: Downloading and running UDx example code
• 1.3: C++ SDK
• 1.3.1: Setting up the C++ SDK
• 1.3.2: Compiling your C++ library
• 1.3.3: Adding metadata to C++ libraries
• 1.3.4: C++ SDK data types
• 1.3.5: Resource use for C++ UDxs
• 1.3.5.1: Allocating resources for UDxs
• 1.3.5.2: Allocating resources with the SDK macros
• 1.3.5.3: Informing Vertica of resource requirements
• 1.3.5.4: Setting memory limits for fenced-mode UDxs
• 1.3.5.5: How resource limits are enforced
• 1.4: Java SDK
• 1.4.1: Setting up the Java SDK
• 1.4.2: Compiling and packaging a Java library
• 1.4.3: Handling Java UDx dependencies
• 1.4.4: Java and Vertica data types
• 1.4.5: Handling NULL values
• 1.4.6: Adding metadata to Java UDx libraries
• 1.4.7: Java UDx resource management
• 1.5: Python SDK
• 1.5.1: Setting up a Python development environment
• 1.5.2: Python and Vertica data types
• 1.6: R SDK
• 1.6.1: Installing/upgrading the R language pack for Vertica
• 1.6.2: R packages
• 1.6.3: R and Vertica data types
• 1.6.4: Adding metadata to R libraries
• 1.6.5: Setting null input and volatility behavior for R functions
• 1.7: Debugging tips
• 2: Arguments and return values
• 2.1: Overloading your UDx
• 2.1.1: C++ example: overloading your UDx
• 2.1.2: Java example: overloading your UDx
• 2.2: Creating a polymorphic UDx
• 2.2.1: C++ example: PolyNthValue
• 2.2.2: Java example: AddAnyInts
• 2.2.3: R example: kmeansPoly
• 3: UDx parameters
• 3.1: Defining UDx parameters
• 3.2: Getting parameter values in UDxs
• 3.3: Calling UDxs with parameters
• 3.4: Specifying the behavior of passing unregistered parameters
• 3.5: User-defined session parameters
• 3.6: C++ example: defining parameters
• 3.7: C++ example: using session parameters
• 3.8: Java example: defining parameters
• 3.9: Java example: using session parameters
• 4: Errors, warnings, and logging
• 4.1: Sending messages
• 4.2: Handling errors
• 4.3: Logging
• 5: Handling cancel requests
• 5.1: Implementing the cancel callback
• 5.2: Checking for cancellation during execution
• 5.3: C++ example: cancelable UDSource
• 6: Aggregate functions (UDAFs)
• 6.1: AggregateFunction class
• 6.2: AggregateFunctionFactory class
• 6.3: UDAF performance in statements containing a GROUP BY clause
• 6.4: C++ example: average
• 7: Analytic functions (UDAnFs)
• 7.1: AnalyticFunction class
• 7.2: AnalyticFunctionFactory class
• 7.3: C++ example: rank
• 8: Scalar functions (UDSFs)
• 8.1: ScalarFunction class
• 8.2: ScalarFunctionFactory class
• 8.3: Setting null input and volatility behavior
• 8.4: Improving query performance (C++ only)
• 8.5: C++ example: Add2Ints
• 8.6: Python example: currency_convert
• 8.7: Python example: validate_url
• 8.8: Python example: matrix multiplication
• 8.9: R example: SalesTaxCalculator
• 8.10: R example: kmeans
• 8.11: C++ example: using complex types
• 8.12: C++ example: returning multiple values
• 8.13: C++ example: calling a UDSF from a check constraint
• 9: Transform functions (UDTFs)
• 9.1: TransformFunction class
• 9.2: TransformFunctionFactory class
• 9.3: MultiPhaseTransformFunctionFactory class
• 9.4: Improving query performance (C++ only)
• 9.5: Partitioning options for UDTFs
• 9.6: C++ example: string tokenizer
• 9.7: Python example: string tokenizer
• 9.8: R example: log tokenizer
• 9.9: C++ example: multi-phase indexer
• 9.10: Python example: multi-phase calculation
• 9.11: Python example: count elements
• 9.12: Python example: explode
• 10: User-defined load (UDL)
• 10.1: User-defined source
• 10.1.1: UDSource class
• 10.1.2: SourceFactory class
• 10.1.3: C++ example: CurlSource
• 10.1.4: C++ example: concurrent load
• 10.1.5: Java example: FileSource
• 10.2: User-defined filter
• 10.2.1: UDFilter class
• 10.2.2: FilterFactory class
• 10.2.3: Java example: ReplaceCharFilter
• 10.2.4: C++ example: converting encoding
• 10.3: User-defined parser
• 10.3.1: UDParser class
• 10.3.2: UDChunker class
• 10.3.3: ParserFactory class
• 10.3.4: C++ example: BasicIntegerParser
• 10.3.5: C++ example: ContinuousIntegerParser
• 10.3.6: Java example: numeric text
• 10.3.7: Java example: JSON parser
• 10.3.8: C++ example: delimited parser and chunker
• 10.3.9: Python example: complex types JSON parser
• 10.4: Load parallelism
• 10.4.1: Cooperative parse
• 10.4.2: Apportioned load
• 10.4.3: Combining cooperative parse and apportioned load
• 10.5: Continuous load
• 10.6: Buffer classes

1 - Developing with the Vertica SDK

Before you can write a user-defined extension you must set up a development environment. After you do so, a good test is to download, build, and run the published examples.

In addition to covering how to set up your environment, this section covers general information about working with the Vertica SDK, including language-specific considerations.

1.1 - Setting up a development environment

Before you start developing your UDx, you need to configure your development and test environments. Development and test environments must use the same operating system and Vertica version as the production environment.

For additional language-specific requirements, see the following topics:

• Setting up the C++ SDK
• Setting up the Java SDK
• Python SDK
• Installing/upgrading the R language pack for Vertica

Development environment options

The language that you use to develop your UDx determines the setup options and requirements for your development environment. C++ developers can use the C++ UDx container, and all developers can use a non-production Vertica environment.

C++ UDx container

C++ developers can develop with the C++ UDx container. The UDx-container GitHub repository provides the tools to build a container that packages the binaries, libraries, and compilers required to develop C++ Vertica extensions. The C++ UDx container has the following build options:

• CentOS or Ubuntu base image

• Vertica 10.x and 11.x versions

For requirement, build, and test details, see the repository README.

Non-production Vertica environments

You can use a node in a non-production Vertica database or another machine that runs the same operating system and Vertica version as your production environment. For specific requirements and dependencies, refer to Operating System Requirements and Language Requirements.

Test environment options

To test your UDx, you need access to a non-production Vertica database. You have the following options:

• Install a single-node Vertica database on your development machine.
• Download and build a containerized test environment.

Containerized test environments

Vertica provides the following containerized options to simplify your test environment setup:

• Vertica Community Edition (CE) container image from the Vertica DockerHub registry. See the Overview for base image and Vertica version details.

  For details about Vertica CE, see Vertica community edition (CE).

• Custom CE image with the one-node-ce GitHub repository. You can build CentOS- and Debian-based containers that are compatible with Vertica 10.x and 11.x versions.

Operating system requirements

Develop your UDx code on the same Linux platform that you use for your production Vertica database cluster. Centos- and Debian-based operating systems each require that you download additional packages.

CentOS-based operating systems

Installations on the following CentOS-based operating systems require the devtoolset-7 package:

• CentOS

• Red Hat Enterprise Linux

• Oracle Enterprise Linux

Consult the documentation for your operating system for the specific installation command.

Debian-based operating systems

Installations on the following Debian-based operating systems require the GCC package version 7 or later:

• Debian

• Ubuntu

• SUSE

• OpenSUSE

Consult the documentation for your operating system for the specific installation command.

1.2 - Downloading and running UDx example code

You can download all of the examples shown in this documentation, and many more, from the Vertica GitHub repository. This repository includes examples of all types of UDxs.

You can download the examples in either of two ways:

• Download the ZIP file. Extract the contents of the file into a directory.

• Clone the repository. Using a terminal window, run the following command:

  $ git clone https://github.com/vertica/UDx-Examples.git
  

The repository includes a makefile that you can use to compile the C++ and Java examples. It also includes .sql files that load and use the examples. See the README file for instructions on compiling and running the examples. To compile the examples you will need g++ or a JDK and make. See Setting up a development environment for related information.

Running the examples not only helps you understand how a UDx works, but also helps you ensure your development environment is properly set up to compile UDx libraries.

See also

• Aggregate functions (UDAFs)
• Analytic functions (UDAnFs)
• Scalar functions (UDSFs)
• Transform functions (UDTFs)
• User-defined load (UDL)

1.3 - C++ SDK

The Vertica SDK supports writing both fenced and unfenced UDxs in C++ 11. You can download, compile, and run the examples; see Downloading and running UDx example code. Running the examples is a good way to verify that your development environment has all needed libraries.

If you do not have access to a Vertica test environment, you can install Vertica on your development machine and run a single node. Each time you rebuild your UDx library, you need to re-install it into Vertica. The following diagram illustrates the typical development cycle.

This section covers C++-specific topics that apply to all UDx types. For information that applies to all languages, see Arguments and return values, UDx parameters, Errors, warnings, and logging, Handling cancel requests and the sections for specific UDx types. For full API documentation, see the C++ SDK Documentation.

1.3.1 - Setting up the C++ SDK

The Vertica C++ Software Development Kit (SDK) is distributed as part of the server installation. It contains the source and header files you need to create your UDx library. For examples that you can compile and run, see Downloading and running UDx example code.

Requirements

At a minimum, install the following on your development machine:

• devtoolset-7 package (CentOS) or GCC package (Debian), including GCC version 7 or later and an up-to-date libstdc++ package.

  Note

  Vertica has not tested UDx builds that use GCC versions later than GCC 8.

• g++ and its associated toolchain, such as ld. Some Linux distributions package g++ separately from GCC.

• A copy of the Vertica SDK.

You must compile with a std flag value of c++11 or later.

The following optional software packages can simplify development:

• make, or some other build-management tool.

• gdb, or some other debugger.

• Valgrind, or similar tools that detect memory leaks.

If you want to use any third-party libraries, such as statistical analysis libraries, you need to install them on your development machine. If you do not statically link these libraries into your UDx library, you must install them on every node in the cluster. See Compiling your C++ library for details.

SDK files

The SDK files are located in the sdk subdirectory under the root Vertica server directory (usually, /opt/vertica/sdk). This directory contains a subdirectory, include, which contains the headers and source files needed to compile UDx libraries.

There are two files in the include directory you need when compiling your UDx:

• Vertica.h is the main header file for the SDK. Your UDx code needs to include this file in order to find the SDK's definitions.

• Vertica.cpp contains support code that needs to be compiled into the UDx library.

Much of the Vertica SDK API is defined in the VerticaUDx.h header file (which is included by the Vertica.h file). If you're curious, you might want to review the contents of this file in addition to reading the API documentation.

Finding the current SDK version

You must develop your UDx using the same SDK version as the database in which you plan to use it. To display the SDK version currently installed on your system, run the following command in vsql:

=> SELECT sdk_version();

Running the examples

You can download the examples from the GitHub repository (see Downloading and running UDx example code). Compiling and running the examples helps you to ensure that your development environment is properly set up.

To compile all of the examples, including the Java examples, issue the following command in the Java-and-C++ directory under the examples directory:

$ make

1.3.2 - Compiling your C++ library

GNU g++ is the only supported compiler for compiling UDx libraries. Always compile your UDx code on the same version of Linux that you use on your Vertica cluster.

When compiling your library, you must always:

• Compile with a -std flag value of c++11 or later.

• Pass the -shared and -fPIC flags to the linker. The simplest method is to just pass these flags to g++ when you compile and link your library.

• Use the -Wno-unused-value flag to suppress warnings when macro arguments are not used. If you do not use this flag, you may get "left-hand operand of comma has no effect" warnings.

• Compile sdk/include/Vertica.cpp and link it into your library. This file contains support routines that help your UDx communicate with Vertica. The easiest way to do this is to include it in the g++ command to compile your library. Vertica supplies this file as C++ source rather than a library to limit library compatibility issues.

• Add the Vertica SDK include directory in the include search path using the g++ -I flag.

The SDK examples include a working makefile. See Downloading and running UDx example code.

Example of compiling a UDx

The following command compiles a UDx contained in a single source file named MyUDx.cpp into a shared library named MyUDx.so:

g++ -I /opt/vertica/sdk/include -Wall -shared -Wno-unused-value \
      -fPIC -o MyUDx.so MyUDx.cpp /opt/vertica/sdk/include/Vertica.cpp

After you debug your UDx, you are ready to deploy it. Recompile your UDx using the -O3 flag to enable compiler optimization.

You can add additional source files to your library by adding them to the command line. You can also compile them separately and then link them together.

Handling external libraries

You must link your UDx library to any supporting libraries that your UDx code relies on.These libraries might be either ones you developed or others provided by third parties. You have two options for linking:

• Statically link the support libraries into your UDx. The benefit of this method is that your UDx library does not rely on external files. Having a single UDx library file simplifies deployment because you just transfer a single file to your Vertica cluster. This method's main drawback is that it increases the size of your UDx library file.

• Dynamically link the library to your UDx. You must sometimes use dynamic linking if a third-party library does not allow static linking. In this case, you must copy the libraries to your Vertica cluster in addition to your UDx library file.

1.3.3 - Adding metadata to C++ libraries

You can add metadata, such as author name, the version of the library, a description of your library, and so on to your library. This metadata lets you track the version of your function that is deployed on a Vertica Analytic Database cluster and lets third-party users of your function know who created the function. Your library's metadata appears in the USER_LIBRARIES system table after your library has been loaded into the Vertica Analytic Database catalog.

You declare the metadata for your library by calling the RegisterLibrary() function in one of the source files for your UDx. If there is more than one function call in the source files for your UDx, whichever gets interpreted last as Vertica Analytic Database loads the library is used to determine the library's metadata.

The RegisterLibrary() function takes eight string parameters:

RegisterLibrary(author,
                library_build_tag,
                library_version,
                library_sdk_version,
                source_url,
                description,
                licenses_required,
                signature);

• author contains whatever name you want associated with the creation of the library (your own name or your company's name for example).

• library_build_tag is a string you want to use to represent the specific build of the library (for example, the SVN revision number or a timestamp of when the library was compiled). This is useful for tracking instances of your library as you are developing them.

• library_version is the version of your library. You can use whatever numbering or naming scheme you want.

• library_sdk_version is the version of the Vertica Analytic Database SDK Library for which you've compiled the library.

  Note

  This field isn't used to determine whether a library is compatible with a version of the Vertica Analytic Database server. The version of the Vertica Analytic Database SDK you use to compile your library is embedded in the library when you compile it. It is this information that Vertica Analytic Database server uses to determine if your library is compatible with it.

• source_url is a URL where users of your function can find more information about it. This can be your company's website, the GitHub page hosting your library's source code, or whatever site you like.

• description is a concise description of your library.

• licenses_required is a placeholder for licensing information. You must pass an empty string for this value.

• signature is a placeholder for a signature that will authenticate your library. You must pass an empty string for this value.

For example, the following code demonstrates adding metadata to the Add2Ints example (see C++ example: Add2Ints).

// Register the factory with Vertica
RegisterFactory(Add2IntsFactory);

// Register the library's metadata.
RegisterLibrary("Whizzo Analytics Ltd.",
                "1234",
                "2.0",
                "7.0.0",
                "http://www.example.com/add2ints",
                "Add 2 Integer Library",
                "",
                "");

Loading the library and querying the USER_LIBRARIES system table shows the metadata supplied in the call to RegisterLibrary():

=> CREATE LIBRARY add2intslib AS '/home/dbadmin/add2ints.so';
CREATE LIBRARY
=> \x
Expanded display is on.
=> SELECT * FROM USER_LIBRARIES WHERE lib_name = 'add2intslib';
-[ RECORD 1 ]-----+----------------------------------------
schema_name       | public
lib_name          | add2intslib
lib_oid           | 45035996273869808
author            | Whizzo Analytics Ltd.
owner_id          | 45035996273704962
lib_file_name     | public_add2intslib_45035996273869808.so
md5_sum           | 732c9e145d447c8ac6e7304313d3b8a0
sdk_version       | v7.0.0-20131105
revision          | 125200
lib_build_tag     | 1234
lib_version       | 2.0
lib_sdk_version   | 7.0.0
source_url        | http://www.example.com/add2ints
description       | Add 2 Integer Library
licenses_required |
signature         |

1.3.4 - C++ SDK data types

The Vertica SDK has typedefs and classes for representing Vertica data types within your UDx code. Using these typedefs ensures data type compatibility between the data your UDx processes and generates and the Vertica database. The following table describes some of the typedefs available. Consult the C++ SDK Documentation for a complete list, as well as lists of helper functions to convert and manipulate these data types.

For information about SDK support for complex data types, see Complex Types as Arguments and Return Values.

Notes

• When making some Vertica SDK API calls (such as VerticaType::getNumericLength()) on objects, make sure they have the correct data type. To minimize overhead and improve performance, most of the APIs do not check the data types of the objects on which they are called. Calling a function on an incorrect data type can result in an error.

• You cannot create instances of VString or VNumeric yourself. You can manipulate the values of existing objects of these classes that Vertica passes to your UDx, and extract values from them. However, only Vertica can instantiate these classes.

1.3.5 - Resource use for C++ UDxs

Your UDxs consume at least a small amount of memory by instantiating classes and creating local variables. This basic memory usage by UDxs is small enough that you do not need to be concerned about it.

If your UDx needs to allocate more than one or two megabytes of memory for data structures, or requires access to additional resources such as files, you must inform Vertica about its resource use. Vertica can then ensure that the resources your UDx requires are available before running a query that uses it. Even moderate memory use (10MB per invocation of a UDx, for example) can become an issue if there are many simultaneous queries that call it.

1.3.5.1 - Allocating resources for UDxs

You have two options for allocating memory and file handles for your user-defined extensions (UDxs):

• Use Vertica SDK macros to allocate resources. This is the best method, since it uses Vertica's own resource manager, and guarantees that resources used by your UDx are reclaimed. See Allocating resources with the SDK macros.

• While not the recommended option, you can allocate resources in your UDxs yourself using standard C++ methods (instantiating objects using new, allocating memory blocks using malloc(), etc.). You must manually free these resources before your UDx exits.

Whichever method you choose, you usually allocate resources in a function named setup() in your UDx class. This function is called after your UDx function object is instantiated, but before Vertica calls it to process data.

If you allocate memory on your own in the setup() function, you must free it in a corresponding function named destroy(). This function is called after your UDx has performed all of its processing. This function is also called if your UDx returns an error (see Handling errors).

The following code fragment demonstrates allocating and freeing memory using a setup() and destroy() function.

class MemoryAllocationExample : public ScalarFunction
{
public:
    uint64* myarray;
    // Called before running the UDF to allocate memory used throughout
    // the entire UDF processing.
    virtual void setup(ServerInterface &srvInterface, const SizedColumnTypes
                        &argTypes)
    {
        try
        {
            // Allocate an array. This memory is directly allocated, rather than
            // letting Vertica do it. Remember to properly calculate the amount
            // of memory you need based on the data type you are allocating.
            // This example divides 500MB by 8, since that's the number of
            // bytes in a 64-bit unsigned integer.
            myarray = new uint64[1024 * 1024 * 500 / 8];
        }
        catch (std::bad_alloc &ba)
        {
            // Always check for exceptions caused by failed memory
            // allocations.
            vt_report_error(1, "Couldn't allocate memory :[%s]", ba.what());
        }

    }

    // Called after the UDF has processed all of its information. Use to free
    // any allocated resources.
    virtual void destroy(ServerInterface &srvInterface, const SizedColumnTypes
                          &argTypes)
    {
        // srvInterface.log("RowNumber processed %d records", *count_ptr);
        try
        {
            // Properly dispose of the allocated memory.
            delete[] myarray;
        }
        catch (std::bad_alloc &ba)
        {
            // Always check for exceptions caused by failed memory
            // allocations.
            vt_report_error(1, "Couldn't free memory :[%s]", ba.what());
        }

    }

1.3.5.2 - Allocating resources with the SDK macros

The Vertica SDK provides three macros to allocate memory:

• vt_alloc allocates a block of memory to fit a specific data type (vint, struct, etc.).

• vt_allocArray allocates a block of memory to hold an array of a specific data type.

• vt_allocSize allocates an arbitrarily-sized block of memory.

All of these macros allocate their memory from memory pools managed by Vertica. The main benefit of allowing Vertica to manage your UDx's memory is that the memory is automatically reclaimed after your UDx has finished. This ensures there is no memory leaks in your UDx.

Because Vertica frees this memory automatically, do not attempt to free any of the memory you allocate through any of these macros. Attempting to free this memory results in run-time errors.

1.3.5.3 - Informing Vertica of resource requirements

When you run your UDx in fenced mode, Vertica monitors its use of memory and file handles. If your UDx uses more than a few megabytes of memory or any file handles, it should tell Vertica about its resource requirements. Knowing the resource requirements of your UDx allows Vertica to determine whether it can run the UDx immediately or needs to queue the request until enough resources become available to run it.

Determining how much memory your UDx requires can be difficult in some cases. For example, if your UDx extracts unique data elements from a data set, there is potentially no bound on the number of data items. In this case, a useful technique is to run your UDx in a test environment and monitor its memory use on a node as it handles several differently-sized queries, then extrapolate its memory use based on the worst-case scenario it may face in your production environment. In all cases, it's usually a good idea to add a safety margin to the amount of memory you tell Vertica your UDx uses.

Your UDx informs Vertica of its resource needs by implementing the getPerInstanceResources() function in its factory class (see Vertica::UDXFactory::getPerInstanceResources() in the SDK documentation). If your UDx's factory class implements this function, Vertica calls it to determine the resources your UDx requires.

The getPerInstanceResources() function receives an instance of the Vertica::VResources struct. This struct contains fields that set the amount of memory and the number of file handles your UDx needs. By default, the Vertica server allocates zero bytes of memory and 100 file handles for each instance of your UDx.

Your implementation of the getPerInstanceResources() function sets the fields in the VResources struct based on the maximum resources your UDx may consume for each instance of the UDx function. So, if your UDx's processBlock() function creates a data structure that uses at most 100MB of memory, your UDx must set the VResources.scratchMemory field to at least 104857600 (the number of bytes in 100MB). Leave yourself a safety margin by increasing the number beyond what your UDx should normally consume. In this example, allocating 115000000 bytes (just under 110MB) is a good idea.

The following ScalarFunctionFactory class demonstrates calling getPerInstanceResources() to inform Vertica about the memory requirements of the MemoryAllocationExample class shown in Allocating resources for UDxs. It tells Vertica that the UDSF requires 510MB of memory (which is a bit more than the UDSF actually allocates, to be on the safe size).

class MemoryAllocationExampleFactory : public ScalarFunctionFactory
{
    virtual Vertica::ScalarFunction *createScalarFunction(Vertica::ServerInterface
                                                            &srvInterface)
    {
        return vt_createFuncObj(srvInterface.allocator, MemoryAllocationExample);
    }
    virtual void getPrototype(Vertica::ServerInterface &srvInterface,
                              Vertica::ColumnTypes &argTypes,
                              Vertica::ColumnTypes &returnType)
    {
        argTypes.addInt();
        argTypes.addInt();
        returnType.addInt();
    }
    // Tells Vertica the amount of resources that this UDF uses.
    virtual void getPerInstanceResources(ServerInterface &srvInterface,
                                          VResources &res)
    {
        res.scratchMemory += 1024LL * 1024 * 510; // request 510MB of memory
    }
};

1.3.5.4 - Setting memory limits for fenced-mode UDxs

Vertica calls a fenced-mode UDx's implementation of Vertica::UDXFactory::getPerInstanceResources() to determine if there are enough free resources to run the query containing the UDx (see Informing Vertica of resource requirements). Since these reports are not generated by actual memory use, they can be inaccurate. Once started by Vertica, a UDx could allocate far more memory or file handles than it reported it needs.

The FencedUDxMemoryLimitMB configuration parameter lets you create an absolute memory limit for UDxs. Any attempt by a UDx to allocate more memory than this limit results in a bad_alloc exception. For an example of setting FencedUDxMemoryLimitMB, see How resource limits are enforced.

1.3.5.5 - How resource limits are enforced

Before running a query, Vertica determines how much memory it requires to run. If the query contains a fenced-mode UDx which implements the getPerInstanceResources() function in its factory class, Vertica calls it to determine the amount of memory the UDx needs and adds this to the total required for the query. Based on these requirements, Vertica decides how to handle the query:

• If the total amount of memory required (including the amount that the UDxs report that they need) is larger than the session's MEMORYCAP or resource pool's MAXMEMORYSIZE setting, Vertica rejects the query. For more information about resource pools, see Resource pool architecture.

• If the amount of memory is below the limit set by the session and resource pool limits, but there is currently not enough free memory to run the query, Vertica queues it until enough resources become available.

• If there are enough free resources to run the query, Vertica executes it.

If the process executing your UDx attempts to allocate more memory than the limit set by the FencedUDxMemoryLimitMB configuration parameter, it receives a bad_alloc exception. For more information about FencedUDxMemoryLimitMB, see Setting memory limits for fenced-mode UDxs.

Below is the output of loading a UDSF that consumes 500MB of memory, then changing the memory settings to cause out-of-memory errors. The MemoryAllocationExample UDSF in the following example is just the Add2Ints UDSF example altered as shown in Allocating resources for UDxs and Informing Vertica of resource requirements to allocate 500MB of RAM.

=> CREATE LIBRARY mylib AS '/home/dbadmin/MemoryAllocationExample.so';
CREATE LIBRARY
=> CREATE FUNCTION usemem AS NAME 'MemoryAllocationExampleFactory' LIBRARY mylib
-> FENCED;
CREATE FUNCTION
=> SELECT usemem(1,2);
 usemem
--------
      3
(1 row)

The following statements demonstrate setting the session's MEMORYCAP to lower than the amount of memory that the UDSF reports it uses. This causes Vertica to return an error before it executes the UDSF.

=> SET SESSION MEMORYCAP '100M';
SET
=> SELECT usemem(1,2);
ERROR 3596:  Insufficient resources to execute plan on pool sysquery
[Request exceeds session memory cap: 520328KB > 102400KB]
=> SET SESSION MEMORYCAP = default;
SET

The resource pool can also prevent a UDx from running if it requires more memory than is available in the pool. The following statements demonstrate the effect of creating and using a resource pool that has too little memory for the UDSF to run. Similar to the session's MAXMEMORYCAP limit, the pool's MAXMEMORYSIZE setting prevents Vertica from executing the query containing the UDSF.

=> CREATE RESOURCE POOL small MEMORYSIZE '100M' MAXMEMORYSIZE '100M';
CREATE RESOURCE POOL
=> SET SESSION RESOURCE POOL small;
SET
=> CREATE TABLE ExampleTable(a int, b int);
CREATE TABLE
=> INSERT /*+direct*/ INTO ExampleTable VALUES (1,2);
 OUTPUT
--------
      1
(1 row)
=> SELECT usemem(a, b) FROM ExampleTable;
ERROR 3596:  Insufficient resources to execute plan on pool small
[Request Too Large:Memory(KB) Exceeded: Requested = 523136, Free = 102400 (Limit = 102400, Used = 0)]
=> DROP RESOURCE POOL small; --Dropping the pool resets the session's pool
DROP RESOURCE POOL

Finally, setting the FencedUDxMemoryLimitMB configuration parameter to lower than the UDx actually allocates results in the UDx throwing an exception. This is a different case than either of the previous two examples, since the query actually executes. The UDx's code needs to catch and handle the exception. In this example, it uses the vt_report_error macro to report the error back to Vertica and exit.

=> ALTER DATABASE DEFAULT SET FencedUDxMemoryLimitMB = 300;

=> SELECT usemem(1,2);
    ERROR 3412:  Failure in UDx RPC call InvokeSetup(): Error calling setup() in
    User Defined Object [usemem] at [MemoryAllocationExample.cpp:32], error code:
     1, message: Couldn't allocate memory :[std::bad_alloc]

=> ALTER DATABASE DEFAULT SET FencedUDxMemoryLimitMB = -1;

=> SELECT usemem(1,2);
 usemem
--------
      3
(1 row)

See also

• SET SESSION RESOURCE_POOL
• SET SESSION MEMORYCAP

1.4 - Java SDK

The Vertica SDK supports writing Java UDxs of all types except aggregate functions. All Java UDxs are fenced.

You can download, compile, and run the examples; see Downloading and running UDx example code. Running the examples is a good way to verify that your development environment has all needed libraries.

If you do not have access to a Vertica test environment, you can install Vertica on your development machine and run a single node. Each time you rebuild your UDx library, you need to re-install it into Vertica. The following diagram illustrates the typical development cycle.

This section covers Java-specific topics that apply to all UDx types. For information that applies to all languages, see Arguments and return values, UDx parameters, Errors, warnings, and logging, Handling cancel requests and the sections for specific UDx types. For full API documentation, see the Java SDK Documentation.

1.4.1 - Setting up the Java SDK

The Vertica Java Software Development Kit (SDK) is distributed as part of the server installation. It contains the source and JAR files you need to create your UDx library. For examples that you can compile and run, see Downloading and running UDx example code.

Requirements

At a minimum, install the following on your development machine:

• The Java Development Kit (JDK) version that matches the Java version you have installed on your database hosts (see Installing Java on Vertica Hosts).

• A copy of the Vertica SDK.

Optionally, you can simplify development with a build-management tool, such as make.

SDK files

To use the SDK you need two files from the Java support package:

• /opt/vertica/bin/VerticaSDK.jar contains the Vertica Java SDK and other supporting files.

• /opt/vertica/sdk/BuildInfo.java contains version information about the SDK. You must compile this file and include it within your Java UDx JAR files.

If you are not doing your development on a database node, you can copy these two files from one of the database nodes to your development system.

The BuildInfo.java and VerticaSDK.jar files that you use to compile your UDx must be from the same SDK version. Both files must also match the version of the SDK files on your Vertica hosts. Versioning is only an issue if you are not compiling your UDxs on a Vertica host. If you are compiling on a separate development system, always refresh your copies of these two files and recompile your UDxs just before deploying them.

Finding the current SDK version

You must develop your UDx using the same SDK version as the database in which you plan to use it. To display the SDK version currently installed on your system, run the following command in vsql:

=> SELECT sdk_version();

Compiling BuildInfo.java

You need to compile the BuildInfo.java file into a class file, so you can include it in your Java UDx JAR library. If you are using a Vertica node as a development system, you can either:

• Copy the BuildInfo.java file to another location on your host.

• If you have root privileges, compile the BuildInfo.java file in place. (Only the root user has privileges to write files to the /opt/vertica/sdk directory.)

Compile the file using the following command. Replace path with the path to the file and output-directory with the directory where you will compile your UDxs.

$ javac -classpath /opt/vertica/bin/VerticaSDK.jar \
      /path/BuildInfo.java -d output-directory

If you use an IDE such as Eclipse, you can include the BuildInfo.java file in your project instead of compiling it separately. You must also add the VerticaSDK.jar file to the project's build path. See your IDE's documentation for details on how to include files and libraries in your projects.

Running the examples

You can download the examples from the GitHub repository (see Downloading and running UDx example code). Compiling and running the examples helps you to ensure that your development environment is properly set up.

If you have not already done so, set the JAVA_HOME environment variable to your JDK (not JRE) directory.

To compile all of the examples, including the Java examples, issue the following command in the Java-and-C++ directory under the examples directory:

$ make

To compile only the Java examples, issue the following command in the Java-and-C++ directory under the examples directory:

$ make JavaFunctions

1.4.2 - Compiling and packaging a Java library

Before you can use your Java UDx, you need to compile it and package it into a JAR file.

The SDK examples include a working makefile. See Downloading and running UDx example code.

Compile your Java UDx

You must include the SDK JAR file in the CLASSPATH when you compile your Java UDx source files so the Java compiler can resolve the Vertica API calls. If you are using the command-line Java compiler on a host in your database cluster, enter this command:

$ javac -classpath /opt/vertica/bin/VerticaSDK.jar factorySource.java \
      [functionSource.java...] -d output-directory

If all of your source files are in the same directory, you can use *.java on the command line instead of listing the files individually.

If you are using an IDE, verify that a copy of the VerticaSDK.jar file is in the build path.

UDx class file organization

After you compile your UDx, you must package its class files and the BuildInfo.class file into a JAR file.

To use the jar command packaged as part of the JDK, you must organize your UDx class files into a directory structure matching your class package structure. For example, suppose your UDx's factory class has a fully-qualified name of com.mycompany.udfs.Add2ints. In this case, your class files must be in the directory hierarchy com/mycompany/udfs relative to your project's base directory. In addition, you must have a copy of the BuildInfo.class file in the path com/vertica/sdk so that it can be included in the JAR file. This class must appear in your JAR file to indicate the SDK version that was used to compile your Java UDx.

The JAR file for the Add2ints UDSF example has the following directory structure after compilation:

com/vertica/sdk/BuildInfo.class
com/mycompany/example/Add2intsFactory.class
com/mycompany/example/Add2intsFactory$Add2ints.class

Package your UDx into a JAR file

To create a JAR file from the command line:

1. Change to the root directory of your project.

2. Use the jar command to package the BuildInfo.class file and all of the classes in your UDx:

   # jar -cvf libname.jar com/vertica/sdk/BuildInfo.class \
          packagePath/*.class
   

   When you type this command, libname is the filename you have chosen for your JAR file (choose whatever name you like), and packagePath is the path to the directory containing your UDx's class files.

   • For example, to package the files from the Add2ints example, you use the command:

     # jar -cvf Add2intsLib.jar com/vertica/sdk/BuildInfo.class \
     com/mycompany/example/*.class
     

   • More simply, if you compiled BuildInfo.class and your class files into the same root directory, you can use the following command:

     # jar -cvf Add2intsLib.jar .
     

   You must include all of the class files that make up your UDx in your JAR file. Your UDx always consists of at least two classes (the factory class and the function class). Even if you defined your function class as an inner class of your factory class, Java generates a separate class file for the inner class.

After you package your UDx into a JAR file, you are ready to deploy it to your Vertica database.

1.4.3 - Handling Java UDx dependencies

If your Java UDx relies on one or more external libraries, you can handle the dependencies in one of three ways:

• Bundle the JAR files into your UDx JAR file using a tool such as One-JAR or Eclipse Runnable JAR Export Wizard.

• Unpack the JAR file and then repack its contents in your UDx's JAR file.

• Copy the libraries to your Vertica cluster in addition to your UDx library.Then, use the DEPENDS keyword of the CREATE LIBRARY statement to tell Vertica that the UDx library depends on the external libraries. This keyword acts as a library-specific CLASSPATH setting. Vertica distributes the support libraries to all of the nodes in the cluster and sets the class path for the UDx so it can find them.

  If your UDx depends on native libraries (SO files), use the DEPENDS keyword to specify their path. When you call System.loadLibrary in your UDx (which you must do before using a native library), this function uses the DEPENDS path to find them. You do not need to also set the LD_LIBRARY_PATH environment variable.

External library example

The following example demonstrates using an external library with a Java UDx.

The following sample code defines a simple class, named VowelRemover. It contains a single method, named removevowels, that removes all of the vowels (the letters a, e, i, o u, and y) from a string.

package com.mycompany.libs;

public class VowelRemover {
    public String removevowels(String input) {
        return input.replaceAll("(?i)[aeiouy]", "");
    }
};

You can compile this class and package it into a JAR file with the following commands:

$ javac -g com/mycompany/libs/VowelRemover.java
$ jar cf mycompanylibs.jar com/mycompany/libs/VowelRemover.class

The following code defines a Java UDSF, named DeleteVowels, that uses the library defined in the preceding example code. DeleteVowels accepts a single VARCHAR as input, and returns a VARCHAR.

package com.mycompany.udx;
// Import the support class created earlier
import com.mycompany.libs.VowelRemover;
// Import the Vertica SDK
import com.vertica.sdk.*;

public class DeleteVowelsFactory extends ScalarFunctionFactory {

    @Override
    public ScalarFunction createScalarFunction(ServerInterface arg0) {
        return new DeleteVowels();
    }

    @Override
    public void getPrototype(ServerInterface arg0, ColumnTypes argTypes,
            ColumnTypes returnTypes) {
        // Accept a single string and return a single string.
        argTypes.addVarchar();
        returnTypes.addVarchar();
    }

    @Override
    public void getReturnType(ServerInterface srvInterface,
            SizedColumnTypes argTypes,
            SizedColumnTypes returnType){
        returnType.addVarchar(
        // Output will be no larger than the input.
        argTypes.getColumnType(0).getStringLength(), "RemovedVowels");
    }

    public class DeleteVowels extends ScalarFunction
    {
        @Override
        public void processBlock(ServerInterface arg0, BlockReader argReader,
                BlockWriter resWriter) throws UdfException, DestroyInvocation {

            // Create an instance of the  VowelRemover object defined in
            // the library.
            VowelRemover remover = new VowelRemover();

            do {
                String instr = argReader.getString(0);
                // Call the removevowels method defined in the library.
                resWriter.setString(remover.removevowels(instr));
                resWriter.next();
            } while (argReader.next());
        }
    }

}

Use the following commands to build the example UDSF and package it into a JAR:

• The first javac command compiles the SDK’s BuildInfo class. Vertica requires all UDx libraries to contain this class. The javac command’s -d option outputs the class file in the directory structure of your UDSF’s source.

• The second javac command compiles the UDSF class. It adds the previously-created mycompanylibs.jar file to the class path so compiler can find the the VowelRemover class.

• The jar command packages the BuildInfo and the classes for the UDx library together.

$ javac -g -cp /opt/vertica/bin/VerticaSDK.jar\
   /opt/vertica/sdk/com/vertica/sdk/BuildInfo.java -d .
$ javac -g -cp mycompanylibs.jar:/opt/vertica/bin/VerticaSDK.jar\
  com/mycompany/udx/DeleteVowelsFactory.java
$ jar cf DeleteVowelsLib.jar com/mycompany/udx/*.class \
   com/vertica/sdk/*.class

To install the UDx library, you must copy both of the JAR files to a node in the Vertica cluster. Then, connect to the node to execute the CREATE LIBRARY statement.

The following example demonstrates how to load the UDx library after you copy the JAR files to the home directory of the dbadmin user. The DEPENDS keyword tells Vertica that the UDx library depends on the mycompanylibs.jar file.

=> CREATE LIBRARY DeleteVowelsLib AS
   '/home/dbadmin/DeleteVowelsLib.jar' DEPENDS '/home/dbadmin/mycompanylibs.jar'
   LANGUAGE 'JAVA';
CREATE LIBRARY
=> CREATE FUNCTION deleteVowels AS language 'java' NAME
  'com.mycompany.udx.DeleteVowelsFactory' LIBRARY DeleteVowelsLib;
CREATE FUNCTION
=> SELECT deleteVowels('I hate vowels!');
 deleteVowels
--------------
  ht vwls!
(1 row)

1.4.4 - Java and Vertica data types

The Vertica Java SDK converts Vertica's native data types into the appropriate Java data type. The following table lists the Vertica data types and their corresponding Java data types.

Setting BINARY, VARBINARY, and LONG VARBINARY values

The Vertica BINARY, VARBINARY, and LONG VARBINARY data types are converted as the Java UDx SDK 's VString class. You can also set the value of a column with one of these data types with a ByteBuffer object (or a byte array wrapped in a ByteBuffer) using the PartitionWriter.setStringBytes() method. See the Java API UDx entry for PartitionWriter.setStringBytes() for more information.

Timestamps and time zones

When the SDK converts a Vertica timestamp into a Java timestamp, it uses the time zone of the JVM. If the JVM is running in a different time zone than the one used by Vertica, the results can be confusing.

Vertica stores timestamps in the database in UTC. (If a database time zone is set, the conversion is done at query time.) To prevent errors from the JVM time zone, add the following code to the processing method of your UDx:

TimeZone.setDefault(TimeZone.getTimeZone("UTC"));

Strings

The Java SDK contains a class named StringUtils that assists you when manipulating string data. One of its more useful features is its getStringBytes() method. This method extracts bytes from a String in a way that prevents the creation of invalid strings. If you attempt to extract a substring that would split part of a multi-byte UTF-8 character, getStringBytes() truncates it to the nearest whole character.

1.4.5 - Handling NULL values

Your UDxs must be prepared to handle NULL values. These values usually must be handled separately from regular values.

Reading NULL values

Your UDx reads data from instances of the the BlockReader or PartitionReader classes. If the value of a column is NULL, the methods you use to get data (such as getLong) return a Java null reference. If you attempt to use the value without checking for NULL, the Java runtime will throw a null pointer exception.

You can test for null values before reading columns by using the data-type-specific methods (such as isLongNull, isDoubleNull, and isBooleanNull). For example, to test whether the INTEGER first column of your UDx's input is a NULL, you would use the statement:

// See if the Long value in column 0 is a NULL
if (inputReader.isLongNull(0)) {
    // value is null
    . . .

Writing NULL values

You output NULL values using type-specific methods on the BlockWriter and PartitionWriter classes (such as setLongNull and setStringNull). These methods take the column number to receive the NULL value. In addition, the PartitionWriter class has data-type specific set value methods (such as setLongValue and setStringValue). If you pass these methods a value, they set the output column to that value. If you pass them a Java null reference, they set the output column to NULL.

1.4.6 - Adding metadata to Java UDx libraries

You can add metadata, such as author name, the version of the library, a description of your library, and so on to your library. This metadata lets you track the version of your function that is deployed on a Vertica Analytic Database cluster and lets third-party users of your function know who created the function. Your library's metadata appears in the USER_LIBRARIES system table after your library has been loaded into the Vertica Analytic Database catalog.

To add metadata to your Java UDx library, you create a subclass of the UDXLibrary class that contains your library's metadata. You then include this class within your JAR file. When you load your class into the Vertica Analytic Database catalog using the CREATE LIBRARY statement, looks for a subclass of UDXLibrary for the library's metadata.

In your subclass of UDXLibrary, you need to implement eight getters that return String values containing the library's metadata. The getters in this class are:

• getAuthor() returns the name you want associated with the creation of the library (your own name or your company's name for example).

• getLibraryBuildTag() returns whatever String you want to use to represent the specific build of the library (for example, the SVN revision number or a timestamp of when the library was compiled). This is useful for tracking instances of your library as you are developing them.

• getLibraryVersion() returns the version of your library. You can use whatever numbering or naming scheme you want.

• getLibrarySDKVersion() returns the version of the Vertica Analytic Database SDK Library for which you've compiled the library.

  Note

  This field isn't used to determine whether a library is compatible with a version of the Vertica Analytic Database server. The version of the Vertica Analytic Database SDK you use to compile your library is embedded in the library when you compile it. It is this information that Vertica Analytic Database server uses to determine if your library is compatible with it.

• getSourceUrl() returns a URL where users of your function can find more information about it. This can be your company's website, the GitHub page hosting your library's source code, or whatever site you like.

• getDescription() returns a concise description of your library.

• getLicensesRequired() returns a placeholder for licensing information. You must pass an empty string for this value.

• getSignature() returns a placeholder for a signature that will authenticate your library. You must pass an empty string for this value.

For example, the following code demonstrates creating a UDXLibrary subclass to be included in the Add2Ints UDSF example JAR file (see /opt/vertica/sdk/examples/JavaUDx/ScalarFunctions on any Vertica node).

// Import the UDXLibrary class to hold the metadata
import com.vertica.sdk.UDXLibrary;

public class Add2IntsLibrary extends UDXLibrary
{
    // Return values for the metadata about this library.

    @Override public String getAuthor() {return "Whizzo Analytics Ltd.";}
    @Override public String getLibraryBuildTag() {return "1234";}
    @Override public String getLibraryVersion() {return "1.0";}
    @Override public String getLibrarySDKVersion() {return "7.0.0";}
    @Override public String getSourceUrl() {
        return "http://example.com/add2ints";
    }
    @Override public String getDescription() {
        return "My Awesome Add 2 Ints Library";
    }
    @Override public String getLicensesRequired() {return "";}
    @Override public String getSignature() {return "";}
}

When the library containing the Add2IntsLibrary class loaded, the metadata appears in the USER_LIBRARIES system table:

=> CREATE LIBRARY JavaAdd2IntsLib AS :libfile LANGUAGE 'JAVA';
CREATE LIBRARY
=> CREATE FUNCTION JavaAdd2Ints as LANGUAGE 'JAVA'  name 'com.mycompany.example.Add2IntsFactory' library JavaAdd2IntsLib;
CREATE FUNCTION
=> \x
Expanded display is on.
=> SELECT * FROM USER_LIBRARIES WHERE lib_name = 'JavaAdd2IntsLib';
-[ RECORD 1 ]-----+---------------------------------------------
schema_name       | public
lib_name          | JavaAdd2IntsLib
lib_oid           | 45035996273869844
author            | Whizzo Analytics Ltd.
owner_id          | 45035996273704962
lib_file_name     | public_JavaAdd2IntsLib_45035996273869844.jar
md5_sum           | f3bfc76791daee95e4e2c0f8a8d2737f
sdk_version       | v7.0.0-20131105
revision          | 125200
lib_build_tag     | 1234
lib_version       | 1.0
lib_sdk_version   | 7.0.0
source_url        | http://example.com/add2ints
description       | My Awesome Add 2 Ints Library
licenses_required |
signature         |

1.4.7 - Java UDx resource management

Java Virtual Machines (JVMs) allocate a set amount of memory when they start. This set memory allocation complicates memory management for Java UDxs, because memory cannot be dynamically allocated and freed by the UDx as it is processing data. This is differs from C++ UDxs which can dynamically allocate resources.

To control the amount of memory consumed by Java UDxs, Vertica has a memory pool named jvm that it uses to allocate memory for JVMs. If this memory pool is exhausted, queries that call Java UDxs block until enough memory in the pool becomes free to start a new JVM.

By default, the jvm pool has:

• no memory of its own assigned to it, so it borrows memory from the GENERAL pool.

• its MAXMEMORYSIZE set to either 10% of system memory or 2GB, whichever is smaller.

• its PLANNEDCONCURRENCY set to AUTO, so that it inherits the GENERAL pool's PLANNEDCONCURRENCY setting.

You can view the current settings for the jvm pool by querying the RESOURCE_POOLS table:

=> SELECT MAXMEMORYSIZE,PLANNEDCONCURRENCY FROM V_CATALOG.RESOURCE_POOLS WHERE NAME = 'jvm';
 MAXMEMORYSIZE | PLANNEDCONCURRENCY
---------------+--------------------
 10%           | AUTO

When a SQL statement calls a Java UDx, Vertica checks if the jvm memory pool has enough memory to start a new JVM instance to execute the function call. Vertica starts each new JVM with its heap memory size set to approximately the jvm pool's MAXMEMORYSIZE parameter divided by its PLANNEDCONCURRENCY parameter. If the memory pool does not contain enough memory, the query blocks until another JVM exits and return their memory to the pool.

If your Java UDx attempts to consume more memory than has been allocated to the JVM's heap size, it exits with a memory error. You can attempt to resolve this issue by:

• increasing the jvm pool's MAXMEMORYSIZE parameter.

• decreasing the jvm pool's PLANNEDCONCURRENCY parameter.

• changing your Java UDx's code to consume less memory.

Adjusting the jvm pool

When adjusting the jvm pool to your needs, you must consider two factors:

• the amount of RAM your Java UDx requires to run

• how many concurrent Java UDx functions you expect your database to run

You can learn the amount of memory your Java UDx needs using several methods. For example, your code can use Java's Runtime class to get an estimate of the total memory it has allocated and then log the value using ServerInterface.log(). (An instance of this class is passed to your UDx.) If you have multiple Java UDxs in your database, set the jvm pool memory size based on the UDx that uses the most memory.

The number of concurrent sessions that need to run Java UDxs may not be the same as the global PLANNEDCONCURRENCY setting. For example, you may have just a single user who runs a Java UDx, which means you can lower the jvm pool's PLANNEDCONCURRENCY setting to 1.

When you have an estimate for the amount of RAM and the number of concurrent user sessions that need to run Java UDXs, you can adjust the jvm pool to an appropriate size. Set the pool's MAXMEMORYSIZE to the maximum amount of RAM needed by the most demanding Java UDx multiplied by the number of concurrent user sessions that need to run Java UDxs. Set the pool's PLANNEDCONCURENCY to the numebr of simultaneous user sessions that need to run Java UDxs.

For example, suppose your Java UDx requires up to 4GB of memory to run and you expect up to two user sessions use Java UDx's. You would use the following command to adjust the jvm pool:

=> ALTER RESOURCE POOL jvm MAXMEMORYSIZE '8G' PLANNEDCONCURRENCY 2;

The MEMORYSIZE is set to 8GB, which is the 4GB maximum memory use by the Java UDx multiplied by the 2 concurrent user sessions.

See Managing workloads for more information on tuning the jvm and other resource pools.

Freeing JVM memory

The first time users call a Java UDx during their session, Vertica allocates memory from the jvm pool and starts a new JVM. This JVM remains running for as long as the user's session is open so it can process other Java UDx calls. Keeping the JVM running lowers the overhead of executing multiple Java UDxs by the same session. If the JVM did not remain open, each call to a Java UDx would require additional time for Vertica to allocate resources and start a new JVM. However, having the JVM remain open means that the JVM's memory remains allocated for the life of the session whether or not it will be used again.

If the jvm memory pool is depleted, queries containing Java UDxs either block until memory becomes available or eventually fail due a lack of resources. If you find queries blocking or failing for this reason, you can allocate more memory to the jvm pool and increase its PLANNEDCONCURRENCY. Another option is to ask users to call the RELEASE_JVM_MEMORY function when they no longer need to run Java UDxs. This function closes any JVM belonging to the user's session and returns its allocated memory to the jvm memory pool.

The following example demonstrates querying V_MONITOR.SESSIONS to find the memory allocated to JVMs by all sessions. It also demonstrates how the memory is allocated by a call to a Java UDx, and then freed by calling RELEASE_JVM_MEMORY.

=> SELECT USER_NAME,EXTERNAL_MEMORY_KB FROM V_MONITOR.SESSIONS;
 user_name | external_memory_kb
-----------+---------------
 dbadmin   |             0
(1 row)

=> -- Call a Java UDx
=> SELECT add2ints(123,456);
 add2ints
----------
      579
(1 row)
=> -- JVM is now running and memory is allocated to it.
=> SELECT USER_NAME,EXTERNAL_MEMORY_KB FROM V_MONITOR.SESSIONS;
 USER_NAME | EXTERNAL_MEMORY_KB
-----------+---------------
 dbadmin   |         79705
(1 row)

=> -- Shut down the JVM and deallocate memory
=> SELECT RELEASE_JVM_MEMORY();
           RELEASE_JVM_MEMORY
-----------------------------------------
 Java process killed and memory released
(1 row)

=> SELECT USER_NAME,EXTERNAL_MEMORY_KB FROM V_MONITOR.SESSIONS;
 USER_NAME | EXTERNAL_MEMORY_KB
-----------+---------------
 dbadmin   |             0
(1 row)

In rare cases, you may need to close all JVMs. For example, you may need to free memory for an important query, or several instances of a Java UDx may be taking too long to complete. You can use the RELEASE_ALL_JVM_MEMORY to close all of the JVMs in all user sessions:

=> SELECT USER_NAME,EXTERNAL_MEMORY_KB FROM V_MONITOR.SESSIONS;
  USER_NAME  | EXTERNAL_MEMORY_KB
-------------+---------------
 ExampleUser |         79705
 dbadmin     |         79705
(2 rows)

=> SELECT RELEASE_ALL_JVM_MEMORY();
                           RELEASE_ALL_JVM_MEMORY
-----------------------------------------------------------------------------
 Close all JVM sessions command sent. Check v_monitor.sessions for progress.
(1 row)

=> SELECT USER_NAME,EXTERNAL_MEMORY_KB FROM V_MONITOR.SESSIONS;
 USER_NAME | EXTERNAL_MEMORY_KB
-----------+---------------
 dbadmin   |             0
(1 row)

Notes

• The jvm resource pool is used only to allocate memory for the Java UDx function calls in a statement. The rest of the resources required by the SQL statement come from other memory pools.

• The first time a Java UDx is called, Vertica starts a JVM to execute some Java methods to get metadata about the UDx during the query planning phase. The memory for this JVM is also taken from the jvm memory pool.

1.5 - Python SDK

The Vertica SDK supports writing UDxs of some types in Python 3.

The Python SDK does not require any additional system configuration or header files. This low overhead allows you to develop and deploy new capabilities to your Vertica cluster in a short amount of time.

The following workflow is typical for the Python SDK:

Because Python has an interpreter, you do not have to compile your program before loading the UDx in Vertica. However, you should expect to do some debugging of your code after you create your function and begin testing it in Vertica.

When Vertica calls your UDx, it starts a side process that manages the interaction between the server and the Python interpreter.

This section covers Python-specific topics that apply to all UDx types. For information that applies to all languages, see Arguments and return values, UDx parameters, Errors, warnings, and logging, Handling cancel requests and the sections for specific UDx types. For full API documentation, see the Python SDK.

1.5.1 - Setting up a Python development environment

To avoid problems when loading and executing your UDxs, develop your UDxs using the same version of Python that Vertica uses. To do this without changing your environment for projects that might require other Python versions, you can use a Python virtual environment (venv). You can install libraries that your UDx depends on into your venv and use that path when you create your UDx library with CREATE LIBRARY.

Setting up venv

Set up venv using the Python version bundled with Vertica. If you have direct access to a database node, you can use that Python binary directly to create your venv:

$ /opt/vertica/sbin/python3 -m venv /path/to/new/environment

The result is a directory with a default environment, including a site-packages directory:

$ ls venv/lib/
python3.9
$ ls venv/lib/python3.9/
site-packages

If your UDx depends on libraries that are not packaged with Vertica, install them into this directory:

$ source venv/bin/activate
(venv) $ pip install numpy
...

The lib/python3.9/site-packages directory now contains the installed library. The change affects only your virtual environment.

UDx imports

Your UDx code must import, in addition to any libraries you add, the vertica_sdk library:

# always required:
import vertica_sdk
# other libs:
import numpy as np
# ...

The vertica_sdk library is included as a part of the Vertica server. You do not need to add it to site-packages or declare it as a dependency.

Deployment

For libraries you add, you must declare dependencies when using CREATE LIBRARY. This declaration allows Vertica to find the libraries and distribute them to all database nodes. You can supply a path instead of enumerating the libraries:

=> CREATE OR REPLACE LIBRARY pylib AS
   '/path/to/udx/add2ints.py'
   DEPENDS '/path/to/new/environment/lib/python3.9/site-packages/*'
   LANGUAGE 'Python';

=> CREATE OR REPLACE FUNCTION add2ints AS LANGUAGE 'Python'
   NAME 'add2ints_factory' LIBRARY pylib;

CREATE LIBRARY copies the UDx and the contents of the DEPENDS path and stores them with the database. Vertica then distributes copies to all database nodes.

1.5.2 - Python and Vertica data types

The Vertica Python SDK converts native Vertica data types into the appropriate Python data types. The following table describes some of the data type conversions. Consult the Python SDK for a complete list, as well as lists of helper functions to convert and manipulate these data types.

For information about SDK support for complex data types, see Complex Types as Arguments and Return Values.

1.6 - R SDK

The Vertica R SDK extends the capabilities of the Vertica Analytic Database so you can leverage additional R libraries. Before you can begin developing User Defined Extensions (UDxs) in R, you must install the R Language Pack for Vertica on each of the nodes in your cluster. The R SDK supports scalar and transform functions in fenced mode. Other UDx types are not supported.

The following workflow is typical for the R SDK:

You can find detailed documentation of all of the classes in the Vertica R SDK.

1.6.1 - Installing/upgrading the R language pack for Vertica

To create R UDxs in Vertica, install the R Language Pack package that matches your server version. The R Language Pack includes the R runtime and associated libraries for interfacing with Vertica. You must use this version of the R runtime; you cannot upgrade it.

You must install the R Language Pack on each node in the cluster. The Vertica R Language Pack must be the only R Language Pack installed on the node.

Vertica R language pack prerequisites

The R Language Pack package requires a number of packages for installation and execution. The names of these dependencies vary among Linux distributions. For Vertica-supported Linux platforms the packages are:

• RHEL/CentOS: libfortran, xz-libs, libgomp

• SUSE Linux Enterprise Server: libfortran3, liblzma5, libgomp1

• Debian/Ubuntu: libfortran3, liblzma5, libgomp1

Vertica requires a version of the libgfortran4 library later than 7.1 to create R extensions. The libgfortran library is included by default with the devtool and gcc packages.

Installing the Vertica R language pack

If you use your operating systems package manager, rather than the rpm or dpkg command, for installation, you do not need to manually install the R Language Pack. The native package managers for each supported Linux version are:

• RHEL/CentOS: yum

• SUSE Linux Enterprise Server: zypper

• Debian/Ubuntu: apt-get

• Amazon Linux 2.0: yum

1. Download the R language package by browsing to the Vertica website.

2. On the Support tab, select Customer Downloads.

3. When prompted, log in using your Micro Focus credentials.

4. Located and select the vertica-R-lang_version.rpm or vertica-R-lang_version.deb file for your server version. The R language package version must match your server version to three decimal points.

5. Install the package as root or using sudo:

   • RHEL/CentOS
     

     $ yum install vertica-R-lang-<version>.rpm
     

   • SUSE Linux Enterprise Server

     $ zypper install vertica-R-lang-<version>.rpm
     

   • Debian
     

     $ apt-get install ./vertica-R-lang_<version>.deb
     

   • Amazon Linux 2.0
     

      $ yum install vertica-R-lang-<version>.AMZN.rpm
     

The installer puts the R binary in /opt/vertica/R.

Upgrading the Vertica R language pack

When upgrading, some R packages you have manually installed may not work and may have to be reinstalled. If you do not update your package(s), then R returns an error if the package cannot be used. Instructions for upgrading these packages are below.

1. You must uninstall the R Language package before upgrading Vertica. Any additional R packages you manually installed remain in /opt/vertica/R and are not removed when you uninstall the package.

2. Upgrade your server package as detailed in Upgrading Vertica to a New Version.

3. After the server package has been updated, install the new R Language package on each host.

If you have installed additional R packages, on each node:

1. As root run /opt/vertica/R/bin/R and issue the command:
   

   > update.packages(checkBuilt=TRUE)
   

2. Select a CRAN mirror from the list displayed.

3. You are prompted to update each package that has an update available for it. You must update any packages that you manually installed and are not compatible with the current version of R in the R Language Pack.
   Do NOT update:

   • Rcpp

   • Rinside

   The packages you selected to be updated are installed. Quit R with the command:

   > quit()
   

Vertica UDx functions written in R do not need to be compiled and you do not need to reload your Vertica-R libraries and functions after an upgrade.

1.6.2 - R packages

The Vertica R Language Pack includes the following R packages in addition to the default packages bundled with R:

• Rcpp

• RInside

• IpSolve

• lpSolveAPI

You can install additional R packages not included in the Vertica R Language Pack by using one of two methods. You must install the same packages on all nodes.

Installing R packages

You can install additional R packages by using one of the two following methods.

Using the install.packages() R command:

$ sudo /opt/vertica/R/bin/R
> install.packages("Zelig");

Using CMD INSTALL:

/opt/vertica/R/bin/R CMD INSTALL <path-to-package-tgz>

The installed packages are located in: /opt/vertica/R/library.

1.6.3 - R and Vertica data types

The following data types are supported when passing data to/from an R UDx:

NULL values in Vertica are translated to R NA values when sent to the R function. R NA values are translated into Vertica null values when returned from the R function to Vertica.

1.6.4 - Adding metadata to R libraries

You can add metadata, such as author name, the version of the library, a description of your library, and so on to your library. This metadata lets you track the version of your function that is deployed on a Vertica Analytic Database cluster and lets third-party users of your function know who created the function. Your library's metadata appears in the USER_LIBRARIES system table after your library has been loaded into the Vertica Analytic Database catalog.

You declare the metadata for your library by calling the RegisterLibrary() function in one of the source files for your UDx. If there is more than one function call in the source files for your UDx, whichever gets interpreted last as Vertica Analytic Database loads the library is used to determine the library's metadata.

The RegisterLibrary() function takes eight string parameters:

RegisterLibrary(author,
                library_build_tag,
                library_version,
                library_sdk_version,
                source_url,
                description,
                licenses_required,
                signature);

• author contains whatever name you want associated with the creation of the library (your own name or your company's name for example).

• library_build_tag is a string you want to use to represent the specific build of the library (for example, the SVN revision number or a timestamp of when the library was compiled). This is useful for tracking instances of your library as you are developing them.

• library_version is the version of your library. You can use whatever numbering or naming scheme you want.

• library_sdk_version is the version of the Vertica Analytic Database SDK Library for which you've compiled the library.

  Note

  This field isn't used to determine whether a library is compatible with a version of the Vertica Analytic Database server. The version of the Vertica Analytic Database SDK you use to compile your library is embedded in the library when you compile it. It is this information that Vertica Analytic Database server uses to determine if your library is compatible with it.

• source_url is a URL where users of your function can find more information about it. This can be your company's website, the GitHub page hosting your library's source code, or whatever site you like.

• description is a concise description of your library.

• licenses_required is a placeholder for licensing information. You must pass an empty string for this value.

• signature is a placeholder for a signature that will authenticate your library. You must pass an empty string for this value.

The following example shows how to add metadata to an R UDx.

RegisterLibrary("Speedy Analytics Ltd.",
                "1234",
                "1.0",
                "8.1.0",
                "http://www.example.com/sales_tax_calculator.R",
                "Sales Tax R Library",
                "",
                "")

Loading the library and querying the USER_LIBRARIES system table shows the metadata supplied in the call to RegisterLibrary:

=> CREATE LIBRARY rLib AS '/home/dbadmin/sales_tax_calculator.R' LANGUAGE 'R';
CREATE LIBRARY
=> SELECT * FROM USER_LIBRARIES WHERE lib_name = 'rLib';
-[ RECORD 1 ]-----+---------------------------------------------------------
schema_name       | public
lib_name          | rLib
lib_oid           | 45035996273708350
author            | Speedy Analytics Ltd.
owner_id          | 45035996273704962
lib_file_name     | rLib_02552872a35d9352b4907d3fcd03cf9700a0000000000d3e.R
md5_sum           | 30da555537c4d93c352775e4f31332d2
sdk_version       |
revision          |
lib_build_tag     | 1234
lib_version       | 1.0
lib_sdk_version   | 8.1.0
source_url        | http://www.example.com/sales_tax_calculator.R
description       | Sales Tax R Library
licenses_required |
signature         |
dependencies      |
is_valid          | t
sal_storage_id    | 02552872a35d9352b4907d3fcd03cf9700a0000000000d3e

1.6.5 - Setting null input and volatility behavior for R functions

Vertica supports defining volatility and null-input settings for UDxs written in R. Both settings aid in the performance of your R function.

Volatility settings

Volatility settings describe the behavior of the function to the Vertica optimizer. For example, if you have identical rows of input data and you know the UDx is immutable, then you can define the UDx as IMMUTABLE. This tells the Vertica optimizer that it can return a cached value for subsequent identical rows on which the function is called rather than having the function run on each identical row.

To indicate your UDx's volatility, set the volatility parameter of your R factory function to one of the following values:

If you do not define a volatility, then the function is considered to be VOLATILE.

The following example sets the volatility to STABLE in the multiplyTwoIntsFactory function:

multiplyTwoIntsFactory <- function() {
  list(name                  = multiplyTwoInts,
       udxtype               = c("scalar"),
       intype                = c("float","float"),
       outtype               = c("float"),
       volatility            = c("stable"),
       parametertypecallback = multiplyTwoIntsParameters)
}

Null input behavior

Null input setting determine how to respond to rows that have null input. For example, you can choose to return null if any inputs are null rather than calling the function and having the function deal with a NULL input.

To indicate how your UDx reacts to NULL input, set the strictness parameter of your R factory function to one of the following values:

If you do not define a null input behavior, then the function is called on every row of data regardless of the presence of NULL values.

The following example sets the NULL input behavior to STRICT in the multiplyTwoIntsFactory function:

multiplyTwoIntsFactory <- function() {
  list(name                  = multiplyTwoInts,
       udxtype               = c("scalar"),
       intype                = c("float","float"),
       outtype               = c("float"),
       strictness            = c("strict"),
       parametertypecallback = multiplyTwoIntsParameters)
}

1.7 - Debugging tips

The following tips can help you debug your UDx before deploying it in a production environment.

Use a single node for initial debugging

You can attach to the Vertica process using a debugger such as gdb to debug your UDx code. Doing this in a multi-node environment, however, is very difficult. Therefore, consider setting up a single-node Vertica test environment to initially debug your UDx.

Use logging

Each UDx has an associated ServerInterface instance. The ServerInterface provides functions to write to the Vertica log and, in the C++ API only, a system table. See Logging for more information.

2 - Arguments and return values

For all UDx types except load (UDL), the factory class declares the arguments and return type of the associated function. Factories have two methods for this purpose:

• getPrototype() (required): declares input and output types

• getReturnType() (sometimes required): declares the return types, including length and precision, when applicable

The getPrototype() method receives two ColumnTypes parameters, one for input and one for output. The factory in C++ example: string tokenizer takes a single input string and returns a string:

virtual void getPrototype(ServerInterface &srvInterface,
                          ColumnTypes &argTypes, ColumnTypes &returnType)
{
  argTypes.addVarchar();
  returnType.addVarchar();
}

The ColumnTypes class provides "add" methods for each supported type, like addVarchar(). This class supports complex types with the addArrayType() and addRowType() methods; see Complex Types as Arguments. If your function is polymorphic, you can instead call addAny(). You are then responsible for validating your inputs and outputs. For more information about implementing polymorphic UDxs, see Creating a polymorphic UDx.

The getReturnType() method computes a maximum length for the returned value. If your UDx returns a sized column (a return data type whose length can vary, such as a VARCHAR), a value that requires precision, or more than one value, implement this factory method. (Some UDx types require you to implement it.)

The input is a SizedColumnTypes containing the input argument types along with their lengths. Depending on the input types, add one of the following to the output types:

• CHAR, (LONG) VARCHAR, BINARY, and (LONG) VARBINARY: return the maximum length.

• NUMERIC types: specify the precision and scale.

• TIME and TIMESTAMP values (with or without timezone): specify precision.

• INTERVAL YEAR TO MONTH: specify range.

• INTERVAL DAY TO SECOND: specify precision and range.

• ARRAY: specify the maximum number of array elements.

In the case of the string tokenizer, the output is a VARCHAR and the function determines its maximum length:

// Tell Vertica what our return string length will be, given the input
// string length
virtual void getReturnType(ServerInterface &srvInterface,
                           const SizedColumnTypes &inputTypes,
                           SizedColumnTypes &outputTypes)
{
  // Error out if we're called with anything but 1 argument
  if (inputTypes.getColumnCount() != 1)
    vt_report_error(0, "Function only accepts 1 argument, but %zu provided", inputTypes.getColumnCount());

  int input_len = inputTypes.getColumnType(0).getStringLength();

  // Our output size will never be more than the input size
  outputTypes.addVarchar(input_len, "words");
}

Complex types as arguments and return values

The ColumnTypes class supports ARRAY and ROW types. Arrays have elements and rows have fields, both of which have types that you need to describe. To work with complex types, you build ColumnTypes objects for the array or row and then add them to the ColumnTypes objects representing the function inputs and outputs.

In the following example, the input to a transform function is an array of orders, which are rows, and the output is the individual rows with their positions in the array. An order consists of a shipping address (VARCHAR) and an array of product IDs (INT).

• C++
• Python

void getPrototype(ServerInterface &srv,
            ColumnTypes &argTypes,
            ColumnTypes &retTypes)
    {
        // item ID (int), to be used in an array
        ColumnTypes itemIdProto;
        itemIdProto.addInt();

        // row: order = address (varchar) + array of previously-created item IDs
        ColumnTypes orderProto;
        orderProto.addVarchar();                  /* address */
        orderProto.addArrayType(itemIdProto);     /* array of item ID */

        /* argument (input) is array of orders */
        argTypes.addArrayType(orderProto);

        /* return values: index in the array, order */
        retTypes.addInt();                        /* index of element */
        retTypes.addRowType(orderProto);          /* element return type */
    }

void getReturnType(ServerInterface &srv,
            const SizedColumnTypes &argTypes,
            SizedColumnTypes &retTypes)
    {
        Fields itemIdElementFields;
        itemIdElementFields.addInt("item_id");

        Fields orderFields;
        orderFields.addVarchar(32, "address");
        orderFields.addArrayType(itemIdElementFields[0], "item_id");
        // optional third arg: max length, default unbounded

        /* declare return type */
        retTypes.addInt("index");
        static_cast<Fields &>(retTypes).addRowType(orderFields, "element");

        /* NOTE: presumably we have verified that the arguments match the prototype, so really we could just do this: */
        retTypes.addInt("index");
        retTypes.addArg(argTypes.getColumnType(0).getElementType(), "element");
    }

def getPrototype(self, srv_interface, arg_types, return_type):
    # item ID (int), to be used in an array
    itemIdProto = vertica_sdk.ColumnTypes.makeInt()

    # row (order): address (varchar) + array of previously-created item IDs
    orderProtoFields = vertica_sdk.ColumnTypes.makeEmpty()
    orderProtoFields.addVarchar()  # address
    orderProtoFields.addArrayType(itemIdProto) # array of item ID
    orderProto = vertica_sdk.ColumnTypes.makeRowType(orderProtoFields)

    # argument (input): array of orders
    arg_types.addArrayType(orderProto)

    # return values: index in the array, order
    return_type.addInt();                        # index of element
    return_type.addRowType(orderProto);          # element return type

def getReturnType(self, srv_interface, arg_types, return_type):
    itemsIdElementField = vertica_sdk.SizedColumnTypes.makeInt("item_id")

    orderFields = vertica_sdk.SizedColumnTypes.makeEmpty()
    orderFields.addVarchar(32, "address")
    orderFields.addArrayType(itemIdElementField, 1024, "item_ids")

    # declare return type
    return_type.addInt("index")
    return_type.addRowType(orderFields, "element")

    '''
    NOTE: presumably we have verified that the arguments match the prototype, so really we could just do this:
    return_type.addInt("index")
    return_type.addArrayType(argTypes.getColumnType(0).getElementType(), "element")
    '''

Handling different numbers and types of arguments

You can create UDxs that handle multiple signatures, or even accept all arguments supplied to them by the user, using either overloading or polymorphism.

You can overload your UDx by assigning the same SQL function name to multiple factory classes, each of which defines a unique function signature. When a user uses the function name in a query, Vertica tries to match the signature of the function call to the signatures declared by the factory's getPrototype() method. This is the best technique to use if your UDx needs to accept a few different signatures (for example, accepting two required and one optional argument).

Alternatively, you can write a polymorphic function, writing one factory method instead of several and declaring that it accepts any number and type of arguments. When a user uses the function name in a query, Vertica calls your function regardless of the signature. In exchange for this flexibility, your UDx's main "process" method has to determine whether it can accept the arguments and emit errors if not.

All UDx types can use polymorphic inputs. Transform functions and analytic functions can also use polymorphic outputs. This means that getPrototype() can declare a return type of "any" and set the actual return type at runtime. For example, a function that returns the largest value in an input would return the same type as the input type.

2.1 - Overloading your UDx

You may want your UDx to accept several different signatures (sets of arguments). For example, you might want your UDx to accept:

• One or more optional arguments.

• One or more arguments that can be one of several data types.

• Completely distinct signatures (either all INTEGER or all VARCHAR, for example).

You can create a function with this behavior by creating several factory classes, each of which accepts a different signature (the number and data types of arguments). You can then associate a single SQL function name with all of them. You can use the same SQL function name to refer to multiple factory classes as long as the signature defined by each factory is unique. When a user calls your UDx, Vertica matches the number and types of arguments supplied by the user to the arguments accepted by each of your function's factory classes. If one matches, Vertica uses it to instantiate a function class to process the data.

Multiple factory classes can instantiate the same function class, so you can re-use one function class that is able to process multiple sets of arguments and then create factory classes for each of the function signatures. You can also create multiple function classes if you want.

See the C++ example: overloading your UDx and Java example: overloading your UDx examples.

2.1.1 - C++ example: overloading your UDx

The following example code demonstrates creating a user-defined scalar function (UDSF) that adds two or three integers together. The Add2or3ints class is prepared to handle two or three arguments. The processBlock() function checks the number of arguments that have been passed to it, and adds all two or three of them together. It also exits with an error message if it has been called with less than 2 or more than 3 arguments. In theory, this should never happen, since Vertica only calls the UDSF if the user's function call matches a signature on one of the factory classes you create for your function. In practice, it is a good idea to perform this sanity checking, in case your (or someone else's) factory class inaccurately reports a set of arguments your function class cannot handle.

#include "Vertica.h"
using namespace Vertica;
using namespace std;
// a ScalarFunction that accepts two or three
// integers and adds them together.
class Add2or3ints : public Vertica::ScalarFunction
{
public:
    virtual void processBlock(Vertica::ServerInterface &srvInterface,
                              Vertica::BlockReader &arg_reader,
                              Vertica::BlockWriter &res_writer)
    {
        const size_t numCols = arg_reader.getNumCols();

        // Ensure that only two or three parameters are passed in
        if ( numCols < 2 || numCols > 3)
            vt_report_error(0, "Function only accept 2 or 3 arguments, "
                                "but %zu provided", arg_reader.getNumCols());
      // Add two integers together
        do {
            const vint a = arg_reader.getIntRef(0);
            const vint b = arg_reader.getIntRef(1);
            vint c = 0;
        // Check for third argument, add it in if it exists.
            if (numCols == 3)
                c = arg_reader.getIntRef(2);
            res_writer.setInt(a+b+c);
            res_writer.next();
        } while (arg_reader.next());
    }
};
// This factory accepts function calls with two integer arguments.
class Add2intsFactory : public Vertica::ScalarFunctionFactory
{
    virtual Vertica::ScalarFunction *createScalarFunction(Vertica::ServerInterface
                &srvInterface)
    { return vt_createFuncObj(srvInterface.allocator, Add2or3ints); }
    virtual void getPrototype(Vertica::ServerInterface &srvInterface,
                              Vertica::ColumnTypes &argTypes,
                              Vertica::ColumnTypes &returnType)
    {   // Accept 2 integer values
        argTypes.addInt();
        argTypes.addInt();
        returnType.addInt();
    }
};
RegisterFactory(Add2intsFactory);
// This factory defines a function that accepts 3 ints.
class Add3intsFactory : public Vertica::ScalarFunctionFactory
{
    virtual Vertica::ScalarFunction *createScalarFunction(Vertica::ServerInterface
                &srvInterface)
    { return vt_createFuncObj(srvInterface.allocator, Add2or3ints); }
    virtual void getPrototype(Vertica::ServerInterface &srvInterface,
                              Vertica::ColumnTypes &argTypes,
                              Vertica::ColumnTypes &returnType)
    {   // accept 3 integer values
        argTypes.addInt();
        argTypes.addInt();
        argTypes.addInt();
        returnType.addInt();
    }
};
RegisterFactory(Add3intsFactory);

The example has two ScalarFunctionFactory classes, one for each signature that the function accepts (two integers and three integers). There is nothing unusual about these factory classes, except that their implementation of ScalarFunctionFactory::createScalarFunction() both create Add2or3ints objects.

The final step is to bind the same SQL function name to both factory classes. You can assign multiple factories to the same SQL function, as long as the signatures defined by each factory's getPrototype() implementation are different.

=> CREATE LIBRARY add2or3IntsLib AS '/home/dbadmin/Add2or3Ints.so';
CREATE LIBRARY
=> CREATE FUNCTION add2or3Ints as NAME 'Add2intsFactory' LIBRARY add2or3IntsLib FENCED;
CREATE FUNCTION
=> CREATE FUNCTION add2or3Ints as NAME 'Add3intsFactory' LIBRARY add2or3IntsLib FENCED;
CREATE FUNCTION
=> SELECT add2or3Ints(1,2);
 add2or3Ints
-------------
           3
(1 row)
=> SELECT add2or3Ints(1,2,4);
 add2or3Ints
-------------
           7
(1 row)
=> SELECT add2or3Ints(1,2,3,4); -- Will generate an error
ERROR 3467:  Function add2or3Ints(int, int, int, int) does not exist, or
permission is denied for add2or3Ints(int, int, int, int)
HINT:  No function matches the given name and argument types. You may
need to add explicit type casts

The error message in response to the final call to the add2or3Ints function was generated by Vertica, since it could not find a factory class associated with add2or3Ints that accepted four integer arguments. To expand add2or3Ints further, you could create another factory class that accepted this signature, and either change the Add2or3ints ScalarFunction class or create a totally different class to handle adding more integers together. However, adding more classes to accept each variation in the arguments quickly becomes overwhelming. In that case, you should consider creating a polymorphic UDx.

2.1.2 - Java example: overloading your UDx

The following example code demonstrates creating a user-defined scalar function (UDSF) that adds two or three integers together. The Add2or3ints class is prepared to handle two or three arguments. It checks the number of arguments that have been passed to it, and adds all two or three of them together. The processBlock() method checks whether it has been called with less than 2 or more than 3 arguments. In theory, this should never happen, since Vertica only calls the UDSF if the user's function call matches a signature on one of the factory classes you create for your function. In practice, it is a good idea to perform this sanity checking, in case your (or someone else's) factory class reports that your function class accepts a set of arguments that it actually does not.

// You need to specify the full package when creating functions based on
// the classes in your library.
package com.mycompany.multiparamexample;
// Import the entire Vertica SDK
import com.vertica.sdk.*;
// This ScalarFunction accepts two or three integer arguments. It tests
// the number of input columns to determine whether to read two or three
// arguments as input.
public class Add2or3ints extends ScalarFunction
{
    @Override
    public void processBlock(ServerInterface srvInterface,
                             BlockReader argReader,
                             BlockWriter resWriter)
                throws UdfException, DestroyInvocation
    {
        // See how many arguments were passed in
        int numCols = argReader.getNumCols();

        // Return an error if less than two or more than 3 aerguments
        // were given. This error only occurs if a Factory class that
        // accepts the wrong number of arguments instantiates this
        // class.
        if (numCols < 2 || numCols > 3) {
            throw new UdfException(0,
                "Must supply 2 or 3 integer arguments");
        }

        // Process all of the rows of input.
        do {
            // Get the first two integer arguments from the BlockReader
            long a = argReader.getLong(0);
            long b = argReader.getLong(1);

            // Assume no third argument.
            long c = 0;

            // Get third argument value if it exists
            if (numCols == 3) {
                c = argReader.getLong(2);
            }

            // Process the arguments and come up with a result. For this
            // example, just add the three arguments together.
            long result = a+b+c;

            // Write the integer output value.
            resWriter.setLong(result);

            // Advance the output BlocKWriter to the next row.
            resWriter.next();

            // Continue processing input rows until there are no more.
        } while (argReader.next());
    }
}

The main difference between the Add2ints class and the Add2or3ints class is the inclusion of a section that gets the number of arguments by calling BlockReader.getNumCols(). This class also tests the number of columns it received from Vertica to ensure it is in the range it is prepared to handle. This test will only fail if you create a ScalarFunctionFactory whose getPrototype() method defines a signature that accepts less than two or more than three arguments. This is not really necessary in this simple example, but for a more complicated class it is a good idea to test the number of columns and data types that Vertica passed your function class.

Within the do loop, Add2or3ints uses a default value of zero if Vertica sent it two input columns. Otherwise, it retrieves the third value and adds that to the other two. Your own class needs to use default values for missing input columns or alter its processing in some other way to handle the variable columns.

You must define your function class in its own source file, rather than as an inner class of one of your factory classes since Java does not allow the instantiation of an inner class from outside its containing class. You factory class has to be available for instantiation by multiple factory classes.

Once you have created a function class or classes, you create a factory class for each signature you want your function class to handle. These factory classes can call individual function classes, or they can all call the same class that is prepared to accept multiple sets of arguments.

The following example's createScalarFunction() method instantiates a member of the Add2or3ints class.

// You will need to specify the full package when creating functions based on
// the classes in your library.
package com.mycompany.multiparamexample;
// Import the entire Vertica SDK
import com.vertica.sdk.*;
public class Add2intsFactory extends ScalarFunctionFactory
{
    @Override
    public void getPrototype(ServerInterface srvInterface,
                             ColumnTypes argTypes,
                             ColumnTypes returnType)
    {
        // Accept two integers as input
        argTypes.addInt();
        argTypes.addInt();
        // writes one integer as output
        returnType.addInt();
    }
    @Override
    public ScalarFunction createScalarFunction(ServerInterface srvInterface)
    {
        // Instantiate the class that can handle either 2 or 3 integers.
        return new Add2or3ints();
    }
}

The following ScalarFunctionFactory subclass accepts three integers as input. It, too, instantiates a member of the Add2or3ints class to process the function call:

// You will need to specify the full package when creating functions based on
// the classes in your library.
package com.mycompany.multiparamexample;
// Import the entire Vertica SDK
import com.vertica.sdk.*;
public class Add3intsFactory extends ScalarFunctionFactory
{
    @Override
    public void getPrototype(ServerInterface srvInterface,
                             ColumnTypes argTypes,
                             ColumnTypes returnType)
    {
        // Accepts three integers as input
        argTypes.addInt();
        argTypes.addInt();
        argTypes.addInt();
        // Returns a single integer
        returnType.addInt();
    }
    @Override
    public ScalarFunction createScalarFunction(ServerInterface srvInterface)
    {
        // Instantiates the Add2or3ints ScalarFunction class, which is able to
        // handle eitehr 2 or 3 integers as arguments.
        return new Add2or3ints();
    }
}

The factory classes and the function class or classes they call must be packaged into the same JAR file (see Compiling and packaging a Java library for details). If a host in the database cluster has the JDK installed on it, you could use the following commands to compile and package the example:

$ cd pathToJavaProject$ javac -classpath /opt/vertica/bin/VerticaSDK.jar \
> com/mycompany/multiparamexample/*.java
$ jar -cvf Add2or3intslib.jar com/vertica/sdk/BuildInfo.class \
> com/mycompany/multiparamexample/*.class
added manifest
adding: com/vertica/sdk/BuildInfo.class(in = 1202) (out= 689)(deflated 42%)
adding: com/mycompany/multiparamexample/Add2intsFactory.class(in = 677) (out= 366)(deflated 45%)
adding: com/mycompany/multiparamexample/Add2or3ints.class(in = 919) (out= 601)(deflated 34%)
adding: com/mycompany/multiparamexample/Add3intsFactory.class(in = 685) (out= 369)(deflated 46%)

Once you have packaged your overloaded UDx, you deploy it the same way as you do a regular UDx, except you use multiple CREATE FUNCTION statements to define the function, once for each factory class.

=> CREATE LIBRARY add2or3intslib as '/home/dbadmin/Add2or3intslib.jar'
-> language 'Java';
CREATE LIBRARY
=> CREATE FUNCTION add2or3ints as LANGUAGE 'Java' NAME 'com.mycompany.multiparamexample.Add2intsFactory' LIBRARY add2or3intslib;
CREATE FUNCTION
=> CREATE FUNCTION add2or3ints as LANGUAGE 'Java' NAME 'com.mycompany.multiparamexample.Add3intsFactory' LIBRARY add2or3intslib;
CREATE FUNCTION

You call the overloaded function the same way you call any other function.

=> SELECT add2or3ints(2,3);
 add2or3ints
-------------
           5
(1 row)
=> SELECT add2or3ints(2,3,4);
 add2or3ints
-------------
           9
(1 row)
=> SELECT add2or3ints(2,3,4,5);
ERROR 3457:  Function add2or3ints(int, int, int, int) does not exist, or permission is denied for add2or3ints(int, int, int, int)
HINT:  No function matches the given name and argument types. You may need to add explicit type casts

The last error was generated by Vertica, not the UDx code. It returns an error if it cannot find a factory class whose signature matches the function call's signature.

Creating an overloaded UDx is useful if you want your function to accept a limited set of potential arguments. If you want to create a more flexible function, you can create a polymorphic function.

2.2 - Creating a polymorphic UDx

Polymorphic UDxs accept any number and type of argument that the user supplies. Transform functions (UDTFs), analytic functions (UDAnFs), and aggregate functions (UDAFs) can define their output return types at runtime, usually based on the input arguments. For example, a UDTF that adds two numbers could return an integer or a float, depending on the input types.

Vertica does not check the number or types of argument that the user passes to the UDx—it just passes the UDx all of the arguments supplied by the user. It is up to your polymorphic UDx's main processing function (for example, processBlock() in user-defined scalar functions) to examine the number and types of arguments it received and determine if it can handle them. UDxs support up to 9800 arguments.

Polymorphic UDxs are more flexible than using multiple factory classes for your function (see Overloading your UDx). They also allow you to write more concise code, instead of writing versions for each data type. The tradeoff is that your polymorphic function needs to perform more work to determine whether it can process its arguments.

Your polymorphic UDx declares that it accepts any number of arguments in its factory's getPrototype() function by calling the addAny() function on the ColumnTypes object that defines its arguments, as follows:

    // C++ example
    void getPrototype(ServerInterface &srvInterface,
                      ColumnTypes &argTypes,
                      ColumnTypes &returnType)
    {
        argTypes.addAny(); // Must be only argument type.
        returnType.addInt(); // or whatever the function returns
    }

This "any parameter" argument type is the only one that your function can declare. You cannot define required arguments and then call addAny() to declare the rest of the signature as optional. If your function has requirements for the arguments it accepts, your process() function must enforce them.

The getPrototype() example shown previously accepts any type and declares that it returns an integer. The following example shows a version of the method that defers resolving the return type until runtime. You can only use the "any" return type for transform and analytic functions.

    void getPrototype(ServerInterface &srvInterface,
                      ColumnTypes &argTypes,
                      ColumnTypes &returnType)
    {
        argTypes.addAny();
        returnType.addAny(); // type determined at runtime
    }

If you use polymorphic return types, you must also define getReturnType() in your factory. This function is called at runtime to determine the actual return type. See C++ example: PolyNthValue for an example.

Polymorphic UDxs and schema search paths

If a user does not supply a schema name as part of a UDx call, Vertica searches each schema in the schema search path for a function whose name and signature match the function call. See Setting search paths for more information about schema search paths.

Because polymorphic UDxs do not have specific signatures associated with them, Vertica initially skips them when searching for a function to handle the function call. If none of the schemas in the search path contain a UDx whose name and signature match the function call, Vertica searches the schema search path again for a polymorphic UDx whose name matches the function name in the function call.

This behavior gives precedence to a UDx whose signature exactly matches the function call. It allows you to create a "catch-all" polymorphic UDx that Vertica calls only when none of the non-polymorphic UDxs with the same name have matching signatures.

This behavior may cause confusion if your users expect the first polymorphic function in the schema search path to handle a function call. To avoid confusion, you should:

• Avoid using the same name for different UDxs. You should always uniquely name UDxs unless you intend to create an overloaded UDx with multiple signatures.

• When you cannot avoid having UDxs with the same name in different schemas, always supply the schema name as part of the function call. Using the schema name prevents ambiguity and ensures that Vertica uses the correct UDx to process your function calls.

2.2.1 - C++ example: PolyNthValue

The PolyNthValue example is an analytic function that returns the value in the Nth row in each partition in its input. This function is a generalization of FIRST_VALUE [analytic] and LAST_VALUE [analytic].

The values can be of any primitive data type.

For the complete source code, see PolymorphicNthValue.cpp in the examples (in /opt/vertica/sdk/examples/AnalyticFunctions/).

Loading and using the example

Load the library and create the function as follows:

=> CREATE LIBRARY AnalyticFunctions AS '/home/dbadmin/AnalyticFns.so';
CREATE LIBRARY

=> CREATE ANALYTIC FUNCTION poly_nth_value AS LANGUAGE 'C++'
   NAME 'PolyNthValueFactory' LIBRARY AnalyticFunctions;
CREATE ANALYTIC FUNCTION

Consider a table of scores for different test groups:

=> SELECT cohort, score FROM trials;
 cohort | score
--------+-------
   1    | 9
   1    | 8
   1    | 7
   3    | 3
   3    | 2
   3    | 1
   2    | 4
   2    | 5
   2    | 6
(9 rows)

Call the function in a query that uses an OVER clause to partition the data. This example returns the second-highest score in each cohort:

=> SELECT cohort, score, poly_nth_value(score USING PARAMETERS n=2) OVER (PARTITION BY cohort) AS nth_value
FROM trials;
 cohort | score | nth_value
--------+-------+-----------
   1    | 9     |         8
   1    | 8     |         8
   1    | 7     |         8
   3    | 3     |         2
   3    | 2     |         2
   3    | 1     |         2
   2    | 4     |         5
   2    | 5     |         5
   2    | 6     |         5
(9 rows)

Factory implementation

The factory declares that the class is polymorphic, and then sets the return type based on the input type. Two factory methods specify the argument and return types.

Use the getPrototype() method to declare that the analytic function takes and returns any type:

    void getPrototype(ServerInterface &srvInterface, ColumnTypes &argTypes, ColumnTypes &returnType)
    {
        // This function supports any argument data type
        argTypes.addAny();

        // Output data type will be the same as the argument data type
        // We will specify that in getReturnType()
        returnType.addAny();
    }

The getReturnType() method is called at runtime. This is where you set the return type based on the input type:

    void getReturnType(ServerInterface &srvInterface, const SizedColumnTypes &inputTypes,
                       SizedColumnTypes &outputTypes)
    {
        // This function accepts only one argument
        // Complain if we find a different number
        std::vector<size_t> argCols;
        inputTypes.getArgumentColumns(argCols); // get argument column indices

        if (argCols.size() != 1)
        {
            vt_report_error(0, "Only one argument is expected but %s provided",
                            argCols.size()? std::to_string(argCols.size()).c_str() : "none");
        }

        // Define output type the same as argument type
        outputTypes.addArg(inputTypes.getColumnType(argCols[0]), inputTypes.getColumnName(argCols[0]));
    }

Function implementation

The analytic function itself is type-agnostic:

    void processPartition(ServerInterface &srvInterface, AnalyticPartitionReader &inputReader,
                          AnalyticPartitionWriter &outputWriter)
    {
        try {
            const SizedColumnTypes &inTypes = inputReader.getTypeMetaData();
            std::vector<size_t> argCols; // Argument column indexes.
            inTypes.getArgumentColumns(argCols);

            vint currentRow = 1;
            bool nthRowExists = false;

            // Find the value of the n-th row
            do {
                if (currentRow == this->n) {
                    nthRowExists = true;
                    break;
                } else {
                    currentRow++;
                }
            } while (inputReader.next());

            if (nthRowExists) {
                do {
                    // Return n-th value
                    outputWriter.copyFromInput(0 /*dest column*/, inputReader,
                                               argCols[0] /*source column*/);
                } while (outputWriter.next());
            } else {
                // The partition has less than n rows
                // Return NULL value
                do {
                    outputWriter.setNull(0);
                } while (outputWriter.next());
            }
        } catch(std::exception& e) {
            // Standard exception. Quit.
            vt_report_error(0, "Exception while processing partition: [%s]", e.what());
        }
    }
};

2.2.2 - Java example: AddAnyInts

The following example shows an implementation of a Java ScalarFunction that adds together two or more integers.

For the complete source code, see AddAnyIntsInfo.java in the examples (in /opt/vertica/sdk/examples/JavaUDx/ScalarFunctions).

Loading and using the example

Load the library and create the function as follows:

=> CREATE LIBRARY JavaScalarFunctions AS '/home/dbadmin/JavaScalarLib.jar' LANGUAGE 'JAVA';
CREATE LIBRARY

=> CREATE FUNCTION addAnyInts AS LANGUAGE 'Java' NAME 'com.vertica.JavaLibs.AddAnyIntsInfo'
   LIBRARY JavaScalarFunctions;
CREATE FUNCTION

Call the function with two or more integer arguments:

=> SELECT addAnyInts(1,2);
 addAnyInts
------------
          3
(1 row)

=> SELECT addAnyInts(1,2,3,40,50,60,70,80,900);
 addAnyInts
------------
       1206
(1 row)

Calling the function with too few arguments, or with non-integer arguments, produces errors that are generated from the processBlock() method. It is up to your UDx to ensure that the user supplies the correct number and types of arguments to your function and exit with an error if it cannot process them.

Function implementation

Most of the work in the example is done by the processBlock() method. It performs two checks on the arguments that have been passed in through the BlockReader object:

• There are at least two arguments.

• The data types of all arguments are integers.

It is up to your polymorphic UDx to determine that all of the input passed to it is valid.

Once the processBlock() method validates its arguments, it loops over them, adding them together.

        @Override
        public void processBlock(ServerInterface srvInterface,
                                 BlockReader arg_reader,
                                 BlockWriter res_writer)
                    throws UdfException, DestroyInvocation
        {
        SizedColumnTypes inTypes = arg_reader.getTypeMetaData();
        ArrayList<Integer> argCols = new ArrayList<Integer>(); // Argument column indexes.
        inTypes.getArgumentColumns(argCols);
        // While we have inputs to process
            do {
        long sum = 0;
        for (int i = 0; i < argCols.size(); ++i){
            long a = arg_reader.getLong(i);
            sum += a;
        }
                res_writer.setLong(sum);
                res_writer.next();
            } while (arg_reader.next());
        }
    }

Factory implementation

The factory declares the number and type of arguments in the getPrototype() function.

    @Override
    public void getPrototype(ServerInterface srvInterface,
                             ColumnTypes argTypes,
                             ColumnTypes returnType)
    {
    argTypes.addAny();
        returnType.addInt();
    }

2.2.3 - R example: kmeansPoly

The following example shows an implementation of a Transform Function (UDTF) that performs kmeans clustering on one or more input columns.

kmeansPoly <- function(v.data.frame,v.param.list) {
  # Computes clusters using the kmeans algorithm.
  #
  # Input: A dataframe and a list of parameters.
  # Output: A dataframe with one column that tells the cluster to which each data
  #         point belongs.
  # Args:
  #  v.data.frame: The data from Vertica cast as an R data frame.
  #  v.param.list: List of function parameters.
  #
  # Returns:
  #  The cluster associated with each data point.
  # Ensure k is not null.
  if(!is.null(v.param.list[['k']])) {
     number_of_clusters <- as.numeric(v.param.list[['k']])
  } else {
    stop("k cannot be NULL! Please use a valid value.")
  }
  # Run the kmeans algorithm.
  kmeans_clusters <- kmeans(v.data.frame, number_of_clusters)
  final.output <- data.frame(kmeans_clusters$cluster)
  return(final.output)
}

kmeansFactoryPoly <- function() {
  # This function tells Vertica the name of the R function,
  # and the polymorphic parameters.
  list(name=kmeansPoly, udxtype=c("transform"), intype=c("any"),
       outtype=c("int"), parametertypecallback=kmeansParameters)
}

kmeansParameters <- function() {
  # Callback function for the parameter types.
  function.parameters <- data.frame(datatype=rep(NA, 1), length=rep(NA,1),
                                    scale=rep(NA,1), name=rep(NA,1))
  function.parameters[1,1] = "int"
  function.parameters[1,4] = "k"
  return(function.parameters)
}

The polymorphic R function declares it accepts any number of arguments in its factory function by specifying "any" as the argument to the intype parameter and optionally the outtype parameter. If you define "any" argument for intype or outtype, then it is the only type that your function can declare for the respective parameter. You cannot define required arguments and then call "any" to declare the rest of the signature as optional. If your function has requirements for the arguments it accepts, your process function must enforce them.

The outtypecallback method is used to indicate the argument types and sizes it has been called with, and is expected to indicate the types and sizes that the function returns. The outtypecallback method can also be used to check for unsupported types and/or number of arguments. For example, the function may require only integers, with no more than 10 of them.

You assign a SQL name to your polymorphic UDx using the same statement you use to assign one to a non-polymorphic UDx. The following statements show how you load and call the polymorphic function from the example.

=> CREATE LIBRARY rlib2 AS '/home/dbadmin/R_UDx/poly_kmeans.R' LANGUAGE 'R';
CREATE LIBRARY
=> CREATE TRANSFORM FUNCTION kmeansPoly AS LANGUAGE 'R' name 'kmeansFactoryPoly' LIBRARY rlib2;
CREATE FUNCTION
=> SELECT spec, kmeansPoly(sl,sw,pl,pw USING PARAMETERS k = 3)
    OVER(PARTITION BY spec) AS Clusters
      FROM iris;
      spec       | Clusters
-----------------+----------
 Iris-setosa     |        1
 Iris-setosa     |        1
 Iris-setosa     |        1
 Iris-setosa     |        1
.
.
.
(150 rows)

3 - UDx parameters

Parameters let you define arguments for your UDxs that remain constant across all of the rows processed by the SQL statement that calls your UDx. Typically, your UDxs accept arguments that come from columns in a SQL statement. For example, in the following SQL statement, the arguments a and b to the add2ints UDSF change value for each row processed by the SELECT statement:

=> SELECT a, b, add2ints(a,b) AS 'sum' FROM example;
a | b  | sum
---+----+-----
1 |  2 |   3
3 |  4 |   7
5 |  6 |  11
7 |  8 |  15
9 | 10 |  19
(5 rows)

Parameters remain constant for all the rows your UDx processes. You can also make parameters optional so that if the user does not supply it, your UDx uses a default value. For example, the following example demonstrates calling a UDSF named add2intsWithConstant that has a single parameter value named constant whose value is added to each the arguments supplied in each row of input:

=> SELECT a, b, add2intsWithConstant(a, b USING PARAMETERS constant=42)
    AS 'a+b+42' from example;
a | b  | a+b+42
---+----+--------
1 |  2 |     45
3 |  4 |     49
5 |  6 |     53
7 |  8 |     57
9 | 10 |     61
(5 rows)

The topics in this section explain how to develop UDxs that accept parameters.

3.1 - Defining UDx parameters

You define the parameters that your UDx accepts in its factory class (ScalarFunctionFactory, AggregateFunctionFactory, and so on) by implementing getParameterType(). This method is similar to getReturnType(): you call data-type-specific methods on a SizedColumnTypes object that is passed in as a parameter. Each function call sets the name, data type, and width or precision (if the data type requires it) of the parameter.

Setting parameter properties (C++ only)

When you add parameters to the getParameterType() function using the C++ API, you can also set properties for each parameter. For example, you can define a parameter as being required by the UDx. Doing so lets the Vertica server know that every UDx invocation must provide the specified parameter, or the query fails.

By passing an object to the SizedColumnTypes::Properties class, you can define the following four parameter properties:

Setting parameter properties (R only)

When using parameters in your R UDx, you must specify a field in the factory function called parametertypecallback. This field points to the callback function that defines the parameters expected by the function. The callback function defines a four-column data frame with the following properties:

If any of the columns are left blank (or the parametertypecallback function is omitted), then Vertica uses default values.

For more information, see Parametertypecallback function.

Redacting UDx parameters

If a parameter name meets any of the following criteria, its value is automatically redacted from logs and system tables like QUERY_REQUESTS:

• Named "secret" or "password"

• Ends with "_secret" or "_password"

3.2 - Getting parameter values in UDxs

Your UDx uses the parameter values it declared in its factory class (see Defining UDx parameters) in its function class's processing method (for example, processBlock() or processPartition()). It gets its parameter values from a ParamReader object, which is available from the ServerInterface object that is passed to your processing method. Reading parameters from this object is similar to reading argument values from BlockReader or PartitionReader objects: you call a data-type-specific function with the name of the parameter to retrieve its value. For example, in C++:

// Get the parameter reader from the ServerInterface to see if there are supplied parameters.
ParamReader paramReader = srvInterface.getParamReader();
// Get the value of an int parameter named constant.
const vint constant = paramReader.getIntRef("constant");

Using parameters in the factory class

In addition to using parameters in your UDx function class, you can also access the parameters in the factory class. You may want to access the parameters to let the user control the input or output values of your function in some way. For example, your UDx can have a parameter that lets the user choose to have your UDx return a single- or double-precision value. The process of accessing parameters in the factory class is the same as accessing it in the function class: get a ParamReader object from the ServerInterface's getParamReader() method, them read the parameter values.

Testing whether the user supplied parameter values

Unlike its handling of arguments, Vertica does not immediately return an error if a user's function call does not include a value for a parameter defined by your UDx's factory class. This means that your function can attempt to read a parameter value that the user did not supply. If it does so, by default Vertica returns a non-existent parameter warning to the user, and the query containing the function call continues.

If you want your parameter to be optional, you can test whether the user supplied a value for the parameter before attempting to access its value. Your function determines if a value exists for a particular parameter by calling the ParamReader's containsParameter() method with the parameter's name. If this call returns true, your function can safely retrieve the value. If this call returns false, your UDx can use a default value or change its processing in some other way to compensate for not having the parameter value. As long as your UDx does not try to access the non-existent parameter value, Vertica does not generate an error or warning about missing parameters.

See C++ example: defining parameters for an example.

3.3 - Calling UDxs with parameters

You pass parameters to a UDx by adding a USING PARAMETERS clause in the function call after the last argument.

• Do not insert a comma between the last argument and the USING PARAMETERS clause.

• After the USING PARAMETERS clause, add one or more parameter definitions, in the following form:

  <parameter name> = <parameter value>
  

• Separate parameter definitions by commas.

Parameter values can be a constant expression (for example 1234 + SQRT(5678)). You cannot use volatile functions (such as RANDOM) in the expression, because they do not return a constant value. If you do supply a volatile expression as a parameter value, by default, Vertica returns an incorrect parameter type warning. Vertica then tries to run the UDx without the parameter value. If the UDx requires the parameter, it returns its own error, which cancels the query.

Calling a UDx with a single parameter

The following example demonstrates how you can call the Add2intsWithConstant UDSF example shown in C++ example: defining parameters:

=> SELECT a, b, Add2intsWithConstant(a, b USING PARAMETERS constant=42) AS 'a+b+42' from example;
 a | b  | a+b+42
---+----+--------
 1 |  2 |     45
 3 |  4 |     49
 5 |  6 |     53
 7 |  8 |     57
 9 | 10 |     61
(5 rows)

To remove the first instance of the number 3, you can call the RemoveSymbol UDSF example:

=> SELECT '3re3mo3ve3sy3mb3ol' original_string, RemoveSymbol('3re3mo3ve3sy3mb3ol' USING PARAMETERS symbol='3');
  original_string   |   RemoveSymbol
--------------------+-------------------
 3re3mo3ve3sy3mb3ol | re3mo3ve3sy3mb3ol
(1 row)

Calling a UDx with multiple parameters

The following example shows how you can call a version of the tokenize UDTF. This UDTF includes parameters to limit the shortest allowed word and force the words to be output in uppercase. Separate multiple parameters with commas.

=> SELECT url, tokenize(description USING PARAMETERS minLength=4, uppercase=true) OVER (partition by url) FROM T;
       url       |   words
-----------------+-----------
 www.amazon.com  | ONLINE
 www.amazon.com  | RETAIL
 www.amazon.com  | MERCHANT
 www.amazon.com  | PROVIDER
 www.amazon.com  | CLOUD
 www.amazon.com  | SERVICES
 www.dell.com    | LEADING
 www.dell.com    | PROVIDER
 www.dell.com    | COMPUTER
 www.dell.com    | HARDWARE
 www.vertica.com | WORLD'S
 www.vertica.com | FASTEST
 www.vertica.com | ANALYTIC
 www.vertica.com | DATABASE
(16 rows)

The following example calls the RemoveSymbol UDSF. By changing the value of the optional parameter, n, you can remove all instances of the number 3:

=> SELECT '3re3mo3ve3sy3mb3ol' original_string, RemoveSymbol('3re3mo3ve3sy3mb3ol' USING PARAMETERS symbol='3', n=6);
  original_string   | RemoveSymbol
--------------------+--------------
 3re3mo3ve3sy3mb3ol | removesymbol
(1 row)

Calling a UDx with optional or incorrect parameters

You can optionally add the Add2intsWithConstant UDSF's constant parameter. Calling this constraint without the parameter does not return an error or warning:

=> SELECT a,b,Add2intsWithConstant(a, b) AS 'sum' FROM example;
 a | b  | sum
---+----+-----
 1 |  2 |   3
 3 |  4 |   7
 5 |  6 |  11
 7 |  8 |  15
 9 | 10 |  19
(5 rows)

Although calling a UDx with incorrect parameters generates a warning, by default, the query still runs. For further information on setting the behavior of your UDx when you supply incorrect parameters, see Specifying the behavior of passing unregistered parameters.

=> SELECT a, b,  add2intsWithConstant(a, b USING PARAMETERS wrongparam=42) AS 'result' from example;
WARNING 4332:  Parameter wrongparam was not registered by the function and cannot
be coerced to a definite data type
 a | b  | result
---+----+--------
 1 |  2 |      3
 3 |  4 |      7
 5 |  6 |     11
 7 |  8 |     15
 9 | 10 |     19
(5 rows)

3.4 - Specifying the behavior of passing unregistered parameters

By default, Vertica issues a warning message when you pass a UDx an unregistered parameter. An unregistered parameter is one that you did not declare in the getParameterType() method.

You can control the behavior of your UDx when you pass it an unregistered parameter by altering the StrictUDxParameterChecking configuration parameter.

Unregistered parameter behavior settings

You can specify the behavior of your UDx in response to one or more unregistered parameters. To do so, set the StrictUDxParameterChecking configuration parameter to one of the following values:

• 0: Allows unregistered parameters to be accessible to the UDx. The ParamReader class's getType() method determines the data type of the unregistered parameter. Vertica does not display any warning or error message.

• 1 (default): Ignores the unregistered parameter and allows the function to run. Vertica displays a warning message.

• 2: Returns an error and does not allow the function to run.

Examples

The following examples demonstrate the behavior you can specify using different values with the StrictUDxParameterChecking parameter.

View the current value of StrictUDxParameterChecking

To view the current value of the StrictUDxParameterChecking configuration parameter, run the following query:

=> \x
Expanded display is on.
=> SELECT * FROM configuration_parameters WHERE parameter_name = 'StrictUDxParameterChecking';
-[ RECORD 1 ]-----------------+------------------------------------------------------------------
node_name                     | ALL
parameter_name                | StrictUDxParameterChecking
current_value                 | 1
restart_value                 | 1
database_value                | 1
default_value                 | 1
current_level                 | DATABASE
restart_level                 | DATABASE
is_mismatch                   | f
groups                        |
allowed_levels                | DATABASE
superuser_only                | f
change_under_support_guidance | f
change_requires_restart       | f
description                   | Sets the behavior to deal with undeclared UDx function parameters

Change the value of StrictUDxParameterChecking

You can change the value of the StrictUDxParameterChecking configuration parameter at the database, node, or session level. For example, you can change the value to '0' to specify that unregistered parameters can pass to the UDx without displaying a warning or error message:

=> ALTER DATABASE DEFAULT SET StrictUDxParameterChecking = 0;
ALTER DATABASE

Invalid parameter behavior with RemoveSymbol

The following example demonstrates how to call the RemoveSymbol UDSF example. The RemoveSymbol UDSF has a required parameter, symbol, and an optional parameter, n. In this case, you do not use the optional parameter.

If you pass both symbol and an additional parameter called wrongParam, which is not declared in the UDx, the behavior of the UDx changes corresponding to the value of StrictUDxParameterChecking.

When you set StrictUDxParameterChecking to '0', the UDx runs normally without a warning. Additionally, wrongParam becomes accessible to the UDx through the ParamReader object of the ServerInterface object:

=> ALTER DATABASE DEFAULT SET StrictUDxParameterChecking = 0;
ALTER DATABASE

=> SELECT '3re3mo3ve3sy3mb3ol' original_string, RemoveSymbol('3re3mo3ve3sy3mb3ol' USING PARAMETERS symbol='3', wrongParam='x');
  original_string   |   RemoveSymbol
--------------------+-------------------
 3re3mo3ve3sy3mb3ol | re3mo3ve3sy3mb3ol
(1 row)

When you set StrictUDxParameterChecking to '1', the UDx ignores wrongParam and runs normally. However, it also issues a warning message:

=> ALTER DATABASE DEFAULT SET StrictUDxParameterChecking = 1;
ALTER DATABASE

=> SELECT '3re3mo3ve3sy3mb3ol' original_string, RemoveSymbol('3re3mo3ve3sy3mb3ol' USING PARAMETERS symbol='3', wrongParam='x');
WARNING 4320:  Parameter wrongParam was not registered by the function and cannot be coerced to a definite data type
  original_string   |   RemoveSymbol
--------------------+-------------------
 3re3mo3ve3sy3mb3ol | re3mo3ve3sy3mb3ol
(1 row)

When you set StrictUDxParameterChecking to '2', the UDx encounters an error when it tries to call wrongParam and does not run. Instead, it generates an error message:

=> ALTER DATABASE DEFAULT SET StrictUDxParameterChecking = 2;
ALTER DATABASE

=> SELECT '3re3mo3ve3sy3mb3ol' original_string, RemoveSymbol('3re3mo3ve3sy3mb3ol' USING PARAMETERS symbol='3', wrongParam='x');
ERROR 0:  Parameter wrongParam was not registered by the function

3.5 - User-defined session parameters

User-defined session parameters allow you to write more generalized parameters than what Vertica provides. You can configure user-defined session parameters in these ways:

• From the client—for example, with ALTER SESSION

• Through the UDx itself

A user-defined session parameter can be passed into any type of UDx supported by Vertica. You can also set parameters for your UDx at the session level. By specifying a user-defined session parameter, you can have the state of a parameter saved continuously. Vertica saves the state of the parameter even when the UDx is invoked multiple times during a single session.

The RowCount example uses a user-defined session parameter. This parameter counts the total number of rows processed by the UDx each time it runs. RowCount then displays the aggregate number of rows processed for all executions. See C++ example: using session parameters and Java example: using session parameters for implementations.

Viewing the user-defined session parameter

Enter the following command to see the value of all session parameters:

=> SHOW SESSION UDPARAMETER all;
schema | library | key | value
--------+---------+-----+-------
(0 rows)

No value has been set, so the table is empty. Now, execute the UDx:

=> SELECT RowCount(5,5);
RowCount
----------
10
(1 row)

Again, enter the command to see the value of the session parameter:

=> SHOW SESSION UDPARAMETER all;
schema |  library  |   key    | value
--------+-----------+----------+-------
public | UDSession | rowcount | 1
(1 row)

The library column shows the name of the library containing the UDx. This is the name set with CREATE LIBRARY. Because the UDx has processed one row, the value of the rowcount session parameter is now 1. Running the UDx two more times should increment the value twice.

=> SELECT RowCount(10,10);
RowCount
----------
20
(1 row)
=> SELECT RowCount(15,15);
RowCount
----------
30
(1 row)

You have now executed the UDx three times, obtaining the sum of 5 + 5, 10 + 10, and 15 + 15. Now, check the value of rowcount.

=> SHOW SESSION UDPARAMETER all;
schema |  library  |   key    | value
--------+-----------+----------+-------
public | UDSession | rowcount | 3
(1 row)

Altering the user-defined session parameter

You can also manually alter the value of rowcount. To do so, enter the following command:

=> ALTER SESSION SET UDPARAMETER FOR UDSession rowcount = 25;
ALTER SESSION

Check the value of RowCount:

=> SHOW SESSION UDPARAMETER all;
schema |  library  |   key    | value
--------+-----------+----------+-------
public | UDSession | rowcount | 25
(1 row)

Clearing the user-defined session parameter

From the client:

To clear the current value of rowcount, enter the following command:

=> ALTER SESSION CLEAR UDPARAMETER FOR UDSession rowcount;
ALTER SESSION

Verify that rowcount has been cleared:

=> SHOW SESSION UDPARAMETER all;
schema | library | key | value
--------+---------+-----+-------
(0 rows)

Through the UDx in C++:

You can set the session parameter to clear through the UDx itself. For example, to clear rowcount when its value reaches 10 or greater, do the following:

1. Remove the following line from the destroy() method in the RowCount class:

   udParams.getUDSessionParamWriter("library").getStringRef("rowCount").copy(i_as_string);
   

2. Replace the removed line from the destroy() method with the following code:

   
   if (rowCount < 10)
   {
   udParams.getUDSessionParamWriter("library").getStringRef("rowCount").copy(i_as_string);
   }
   else
   {
   udParams.getUDSessionParamWriter("library").clearParameter("rowCount");
   }
   

3. To see the UDx clear the session parameter, set rowcount to a value of 9:

   => ALTER SESSION SET UDPARAMETER FOR UDSession rowcount = 9;
   ALTER SESSION
   

4. Check the value of rowcount:

   => SHOW SESSION UDPARAMETER all;
    schema |  library  |   key    | value
   --------+-----------+----------+-------
    public | UDSession | rowcount | 9
    (1 row)
   

5. Invoke RowCount so that its value becomes 10:

   => SELECT RowCount(15,15);
   RowCount
   ----------
         30
    (1 row)
   

6. Check the value of rowcount again. Because the value has reached 10, the threshold specified in the UDx, expect that rowcount is cleared:

   => SHOW SESSION UDPARAMETER all;
    schema | library | key | value
   --------+---------+-----+-------
    (0 rows)
   

   As expected, RowCount is cleared.

Through the UDx in Java:

1. Remove the following lines from the destroy() method in the RowCount class:

   udParams.getUDSessionParamWriter("library").setString("rowCount", Integer.toString(rowCount));
   srvInterface.log("RowNumber processed %d records", count);
   

2. Replace the removed lines from the destroy() method with the following code:

   
   if (rowCount < 10)
   {
   udParams.getUDSessionParamWriter("library").setString("rowCount", Integer.toString(rowCount));
   srvInterface.log("RowNumber processed %d records", count);
   }
   else
   {
   udParams.getUDSessionParamWriter("library").clearParameter("rowCount");
   }
   

3. To see the UDx clear the session parameter, set rowcount to a value of 9:

   => ALTER SESSION SET UDPARAMETER FOR UDSession rowcount = 9;
   ALTER SESSION
   

4. Check the value of rowcount:

   => SHOW SESSION UDPARAMETER all;
    schema |  library  |   key    | value
   --------+-----------+----------+-------
    public | UDSession | rowcount | 9
    (1 row)
   

5. Invoke RowCount so that its value becomes 10:

   => SELECT RowCount(15,15);
   RowCount
   ----------
          30
    (1 row)
   

6. Check the value of rowcount. Since the value has reached 10, the threshold specified in the UDx, expect that rowcount is cleared:

   => SHOW SESSION UDPARAMETER all;
    schema | library | key | value
   --------+---------+-----+-------
    (0 rows)
   

As expected, rowcount is cleared.

Read-only and hidden session parameters

If you don't want a parameter to be set anywhere except in the UDx, you can make it read-only. If, additionally, you don't want a parameter to be visible in the client, you can make it hidden.

To make a parameter read-only, meaning that it cannot be set in the client, but can be viewed, add a single underscore before the parameter's name. For example, to make rowCount read-only, change all instances in the UDx of "rowCount" to "_rowCount".

To make a parameter hidden, meaning that it cannot be viewed in the client nor set, add two underscores before the parameter's name. For example, to make rowCount hidden, change all instances in the UDx of "rowCount" to "__rowCount".

Redacted parameters

If a parameter name meets any of the following criteria, its value is automatically redacted from logs and system tables like QUERY_REQUESTS:

• Named "secret" or "password"

• Ends with "_secret" or "_password"

See also

3.6 - C++ example: defining parameters

The following code fragment demonstrates adding a single parameter to the C++ add2ints UDSF example. The getParameterType() function defines a single integer parameter that is named constant.

class Add2intsWithConstantFactory : public ScalarFunctionFactory
{
    // Return an instance of Add2ints to perform the actual addition.
    virtual ScalarFunction *createScalarFunction(ServerInterface &interface)
    {
        // Calls the vt_createFuncObj to create the new Add2ints class instance.
        return vt_createFuncObj(interface.allocator, Add2intsWithConstant);
    }
    // Report the argument and return types to Vertica.
    virtual void getPrototype(ServerInterface &interface,
                              ColumnTypes &argTypes,
                              ColumnTypes &returnType)
    {
        // Takes two ints as inputs, so add ints to the argTypes object.
        argTypes.addInt();
        argTypes.addInt();
        // Returns a single int.
        returnType.addInt();
    }
    // Defines the parameters for this UDSF. Works similarly to defining arguments and return types.
    virtual void getParameterType(ServerInterface &srvInterface,
                                  SizedColumnTypes &parameterTypes)
    {
        // One int parameter named constant.
        parameterTypes.addInt("constant");
    }
};
RegisterFactory(Add2intsWithConstantFactory);

See the Vertica SDK entry for SizedColumnTypes for a full list of the data-type-specific functions you can call to define parameters.

The following code fragment demonstrates using the parameter value. The Add2intsWithConstant class defines a function that adds two integer values. If the user supplies it, the function also adds the value of the optional integer parameter named constant.

/**
 * A UDSF that adds two numbers together with a constant value.
 *
 */
class Add2intsWithConstant : public ScalarFunction
{
public:
    // Processes a block of data sent by Vertica.
    virtual void processBlock(ServerInterface &srvInterface,
                              BlockReader &arg_reader,
                              BlockWriter &res_writer)
    {
        try
            {
                // The default value for the constant parameter is 0.
                vint constant = 0;

                // Get the parameter reader from the ServerInterface to see if there are supplied parameters.
                ParamReader paramReader = srvInterface.getParamReader();
                // See if the user supplied the constant parameter.
                if (paramReader.containsParameter("constant"))
                    // There is a parameter, so get its value.
                    constant = paramReader.getIntRef("constant");
                // While we have input to process:
                do
                    {
                        // Read the two integer input parameters by calling the BlockReader.getIntRef class function.
                        const vint a = arg_reader.getIntRef(0);
                        const vint b = arg_reader.getIntRef(1);
                        // Add arguments plus constant.
                        res_writer.setInt(a+b+constant);
                        // Finish writing the row, and advance to the next output row.
                        res_writer.next();
                        // Continue looping until there are no more input rows.
                    }
                while (arg_reader.next());
            }
        catch (exception& e)
            {
                // Standard exception. Quit.
                vt_report_error(0, "Exception while processing partition: %s",
                    e.what());
            }
    }
};

3.7 - C++ example: using session parameters

The RowCount example uses a user-defined session parameter, also called RowCount. This parameter counts the total number of rows processed by the UDx each time it runs. RowCount then displays the aggregate number of rows processed for all executions.

#include <string>
#include <sstream>
#include <iostream>
#include "Vertica.h"
#include "VerticaUDx.h"

using namespace Vertica;

class RowCount : public Vertica::ScalarFunction
{
private:
    int rowCount;
    int count;

public:

    virtual void setup(Vertica::ServerInterface &srvInterface, const Vertica::SizedColumnTypes &argTypes) {
        ParamReader pSessionParams = srvInterface.getUDSessionParamReader("library");
        std::string rCount = pSessionParams.containsParameter("rowCount")?
            pSessionParams.getStringRef("rowCount").str(): "0";
        rowCount=atoi(rCount.c_str());

    }
    virtual void processBlock(Vertica::ServerInterface &srvInterface, Vertica::BlockReader &arg_reader, Vertica::BlockWriter &res_writer) {

        count = 0;
        if(arg_reader.getNumCols() != 2)
            vt_report_error(0, "Function only accepts two arguments, but %zu provided", arg_reader.getNumCols());

        do {
            const Vertica::vint a = arg_reader.getIntRef(0);
            const Vertica::vint b = arg_reader.getIntRef(1);
            res_writer.setInt(a+b);
            count++;
            res_writer.next();
        } while (arg_reader.next());

        srvInterface.log("count %d", count);

        }

        virtual void destroy(ServerInterface &srvInterface, const SizedColumnTypes &argTypes, SessionParamWriterMap &udParams) {
            rowCount = rowCount + count;

            std:ostringstream s;
            s << rowCount;
            const std::string i_as_string(s.str());

            udParams.getUDSessionParamWriter("library").getStringRef("rowCount").copy(i_as_string);

        }
};

class RowCountsInfo : public Vertica::ScalarFunctionFactory {
    virtual Vertica::ScalarFunction *createScalarFunction(Vertica::ServerInterface &srvInterface)
    { return Vertica::vt_createFuncObject<RowCount>(srvInterface.allocator);
    }

    virtual void getPrototype(Vertica::ServerInterface &srvInterface, Vertica::ColumnTypes &argTypes, Vertica::ColumnTypes &returnType)
    {
        argTypes.addInt();
        argTypes.addInt();
        returnType.addInt();
    }
};

RegisterFactory(RowCountsInfo);

3.8 - Java example: defining parameters

The following code fragment demonstrates adding a single parameter to the Java add2ints UDSF example. The getParameterType() method defines a single integer parameter that is named constant.

package com.mycompany.example;
import com.vertica.sdk.*;
public class Add2intsWithConstantFactory extends ScalarFunctionFactory
{
    @Override
    public void getPrototype(ServerInterface srvInterface,
                             ColumnTypes argTypes,
                             ColumnTypes returnType)
    {
        argTypes.addInt();
        argTypes.addInt();
        returnType.addInt();
    }

    @Override
    public void getReturnType(ServerInterface srvInterface,
                              SizedColumnTypes argTypes,
                              SizedColumnTypes returnType)
    {
        returnType.addInt("sum");
    }

    // Defines the parameters for this UDSF. Works similarly to defining
    // arguments and return types.
    public void getParameterType(ServerInterface srvInterface,
                              SizedColumnTypes parameterTypes)
    {
        // One INTEGER parameter named constant
        parameterTypes.addInt("constant");
    }

    @Override
    public ScalarFunction createScalarFunction(ServerInterface srvInterface)
    {
        return new Add2intsWithConstant();
    }
}

See the Vertica Java SDK entry for SizedColumnTypes for a full list of the data-type-specific methods you can call to define parameters.

3.9 - Java example: using session parameters

The RowCount example uses a user-defined session parameter, also called RowCount. This parameter counts the total number of rows processed by the UDx each time it runs. RowCount then displays the aggregate number of rows processed for all executions.

package com.mycompany.example;

import com.vertica.sdk.*;

public class RowCountFactory extends ScalarFunctionFactory {

    @Override
    public void getPrototype(ServerInterface srvInterface, ColumnTypes argTypes, ColumnTypes returnType)
    {
        argTypes.addInt();
        argTypes.addInt();
     returnType.addInt();
    }

public class RowCount extends ScalarFunction {

    private Integer count;
    private Integer rowCount;

    // In the setup method, you look for the rowCount parameter. If it doesn't exist, it is created.
    // Look in the default namespace which is "library," but it could be anything else, most likely "public" if not "library".
    @Override
       public void setup(ServerInterface srvInterface, SizedColumnTypes argTypes) {
    count = new Integer(0);
    ParamReader pSessionParams = srvInterface.getUDSessionParamReader("library");
    String rCount = pSessionParams.containsParameter("rowCount")?
    pSessionParams.getString("rowCount"): "0";
    rowCount = Integer.parseInt(rCount);

    }

    @Override
    public void processBlock(ServerInterface srvInterface, BlockReader arg_reader, BlockWriter res_writer)
        throws UdfException, DestroyInvocation {
        do {
        ++count;
        long a = arg_reader.getLong(0);
        long b = arg_reader.getLong(1);

        res_writer.setLong(a+b);
        res_writer.next();
        } while (arg_reader.next());
    }

    @Override
    public void destroy(ServerInterface srvInterface, SizedColumnTypes argTypes, SessionParamWriterMap udParams){
        rowCount = rowCount+count;
        udParams.getUDSessionParamWriter("library").setString("rowCount", Integer.toString(rowCount));
        srvInterface.log("RowNumber processed %d records", count);
        }
    }

    @Override
    public ScalarFunction createScalarFunction(ServerInterface srvInterface){
        return new RowCount();
    }
}

4 - Errors, warnings, and logging

The SDK provides several ways for a UDx to report errors, warnings, and other messages. For a UDx written in C++ or Python, use the messaging APIs described in Sending messages. UDxs in all languages can halt execution with an error, as explained in Handling errors.

UDxs can also write messages to the Vertica log, and UDxs written in C++ can write messages to a system table.

4.1 - Sending messages

A UDx can handle a problem by reporting an error and terminating execution, but in some cases you might want to send a warning and proceed. For example, a UDx might ignore or use a default for an unexpected input and report that it did so. The C++ and Python messaging APIs support reporting messages at different severity levels.

A UDx has access to a ServerInterface instance. This class has the following methods for reporting messages, in order of severity:

• reportError (also terminates execution)

• reportWarning

• reportNotice

• reportInfo

Each method produces messages with the following components:

• ID code: an identification code, any integer. This code does not interact with Vertica error codes.

• Message string: a succinct description of the issue.

• Optional details string: provides more contextual information.

• Optional hint string: provides other guidance.

Duplicate messages are condensed into a single report if they have the same code and message string, even if the details and hint strings differ.

Constructing messages

The UDx should report errors immediately, usually during a process call. For all other message types, record information during processing and call the reporting methods from the UDx's destroy method. The other reporting methods do not produce output if called during processing.

The process of constructing messages is language-specific.

C++

Each ServerInterface reporting method takes a ClientMessage argument. The ClientMessage class has the following methods to set the code and message, detail, and hint:

• makeMessage: sets the ID code and message string.

• setDetail: sets the optional detail string.

• setHint: sets the optional hint string.

These method calls can be chained to simplify creating and passing the message.

All strings support printf-style arguments and formatting.

In the following example, a function records issues in processBlock and reports them in destroy:

class PositiveIdentity : public Vertica::ScalarFunction
    {
public:
    using ScalarFunction::destroy;
    bool hitNotice = false;

    virtual void processBlock(Vertica::ServerInterface &srvInterface,
                              Vertica::BlockReader &arg_reader,
                              Vertica::BlockWriter &res_writer)
    {
        do {
            const Vertica::vint a = arg_reader.getIntRef(0);
            if (a < 0 && a != vint_null) {
                hitNotice = true;
                res_writer.setInt(null);
            } else {
                res_writer.setInt(a);
            }
            res_writer.next();
        } while (arg_reader.next());
    }

    virtual void destroy(ServerInterface &srvInterface,
                         const SizedColumnTypes &argTypes) override
    {
        if (hitNotice) {
            ClientMessage msg = ClientMessage::makeMessage(100, "Passed negative argument")
                                .setDetail("Value set to null");
            srvInterface.reportNotice(msg);
        }
    }
}

Python

Each ServerInterface reporting method has the following positional and keyword arguments:

• idCode: integer ID code, positional argument.

• message: message text, positional argument.

• hint: optional hint text, keyword argument.

• detail: optional detail text, keyword argument.

All arguments support str.format() and f-string formatting.

In the following example, a function records issues in processBlock and reports them in destroy:

class PositiveIdentity(vertica_sdk.ScalarFunction):
    def __init__(self):
        self.hitNotice = False

    def processBlock(self, server_interface, arg_reader, res_writer):
        while True:
            arg = arg_reader.getInt(0)
            if arg < 0 and arg is not None:
                self.hitNotice = True
                res_writer.setNull()
            else:
                res_writer.setInt(arg)
            res_writer.next()
            if not arg_reader.next():
                break

    def destroy(self, srv, argType):
        if self.hitNotice:
            srv.reportNotice(100, "Passed negative arguement", detail="Value set to null")
        return

API

• C++
• Python

// ClientMessage methods
template<typename... Argtypes>
static ClientMessage makeMessage(int errorcode, const char *fmt, Argtypes&&... args);

template <typename... Argtypes>
ClientMessage & setDetail(const char *fmt, Argtypes&&... args);

template <typename... Argtypes>
ClientMessage & setHint(const char *fmt, Argtypes&&... args);

// ServerInterface reporting methods
virtual void reportError(ClientMessage msg);

virtual void reportInfo(ClientMessage msg);

virtual void reportNotice(ClientMessage msg);

virtual void reportWarning(ClientMessage msg);