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Managing system resource usage

You can use the SQL Monitoring APIs (system tables) to track overall resource usage on your cluster.

You can use the Using system tables to track overall resource usage on your cluster. These and the other system tables are described in the Vertica system tables.

If your queries are experiencing errors due to resource unavailability, you can use the following system tables to obtain more details:

System Table Description
RESOURCE_REJECTIONS Monitors requests for resources that are rejected by the Resource manager.
DISK_RESOURCE_REJECTIONS Monitors requests for resources that are rejected due to disk space shortages. See Managing disk space for more information.

When requests for resources of a certain type are being rejected, do one of the following:

  • Increase the resources available on the node by adding more memory, more disk space, and so on. See Managing disk space.

  • Reduce the demand for the resource by reducing the number of users on the system (see Managing sessions), rescheduling operations, and so on.

The LAST_REJECTED_VALUE field in RESOURCE_REJECTIONS indicates the cause of the problem. For example:

  • The message Usage of a single requests exceeds high limit means that the system does not have enough of the resource available for the single request. A common example occurs when the file handle limit is set too low and you are loading a table with a large number of columns.

  • The message Timed out or Canceled waiting for resource reservation usually means that there is too much contention for the resource because the hardware platform cannot support the number of concurrent users using it.

1 - Managing sessions

Vertica provides several methods for database administrators to view and control sessions.

Vertica provides several methods for database administrators to view and control sessions. The methods vary according to the type of session:

  • External (user) sessions are initiated by vsql or programmatic (ODBC or JDBC) connections and have associated client state.

  • Internal (system) sessions are initiated by Vertica and have no client state.

Configuring maximum sessions

The maximum number of per-node user sessions is set by the configuration parameter MaxClientSessions parameter, by default 50. You can set MaxClientSessions parameter to any value between 0 and 1000. In addition to this maximum, Vertica also allows up to five administrative sessions per node.

For example:

=> ALTER DATABASE DEFAULT SET MaxClientSessions = 100;

Viewing sessions

The system table SESSIONS contains detailed information about user sessions and returns one row per session. Superusers have unrestricted access to all database metadata. Access for other users varies according to their privileges.

Interrupting and closing sessions

You can interrupt a running statement with the Vertica function INTERRUPT_STATEMENT. Interrupting a running statement returns a session to an idle state:

  • No statements or transactions are running.

  • No locks are held.

  • The database is doing no work on behalf of the session.

Closing a user session interrupts the session and disposes of all state related to the session, including client socket connections for the target sessions. The following Vertica functions close one or more user sessions:

SELECT statements that call these functions return after the interrupt or close message is delivered to all nodes. The function might return before Vertica completes execution of the interrupt or close operation. Thus, there might be a delay after the statement returns and the interrupt or close takes effect throughout the cluster. To determine if the session or transaction ended, query the SESSIONS system table.

In order to shut down a database, you must first close all user sessions. For more about database shutdown, see Stopping the database.

2 - Managing load streams

You can use system table LOAD_STREAMS to monitor data as it is loaded on your cluster.

You can use system table LOAD_STREAMS to monitor data as it is loaded on your cluster. Several columns in this table showmetrics for each load stream on each node, including the following:

Column name Value...
ACCEPTED_ROW_COUNT Increases during parsing, up to the maximum number of rows in the input file.

Remains zero (0) until all named pipes return an EOF. While COPY awaits an EOF from multiple pipes, it can appear to be hung. However, before canceling the COPY statement, check your system CPU and disk accesses to determine if any activity is in progress.

In a typical load, the PARSE_COMPLETE_PERCENT value can either increase slowly or jump quickly to 100%, if you are loading from named pipes or STDIN.

SORT_COMPLETE_PERCENT Remains at 0 when loading from named pipes or STDIN. After PARSE_COMPLETE_PERCENT reaches 100 percent, SORT_COMPLETE_PERCENT increases to 100 percent.

Depending on the data sizes, a significant lag can occur between the time PARSE_COMPLETE_PERCENT reaches 100 percent and the time SORT_COMPLETE_PERCENT begins to increase.