Creating fault groups

When you define fault groups, Vertica distributes data segments across the cluster.

When you define fault groups, Vertica distributes data segments across the cluster. This allows the cluster to be aware of your cluster topology so it can tolerate correlated failures inherent in your environment, such as a rack failure. For an overview, see High Availability With Fault Groups.

Important

Defining fault groups requires careful and thorough network planning, and a solid understanding of your network topology.

Prerequisites

To define a fault group, you must have:

Superuser privileges
A fault group input file
An existing database

Run the fault group script

As the database administrator, run the fault_group_ddl_generator.py script:
```
python /opt/vertica/scripts/fault_group_ddl_generator.py databasename fault-group-inputfile > sql-filename
```
For example, the following command writes the Python script output to the SQL file fault_group_ddl.sql.
```
$ python /opt/vertica/scripts/fault_group_ddl_generator.py
    VMart fault_groups_VMart.out > fault_group_ddl.sql
```
After the script returns, you can run the SQL file, instead of multiple DDL statements individually.

Tip
Consider saving the input file so you can modify fault groups later—for example, after expanding the cluster or changing the distribution of control nodes.
Using vsql, run the DDL statements in fault_group_ddl.sql or execute the commands in the file using vsql.
```
=> \i fault_group_ddl.sql
```
If large cluster is enabled, realign control nodes with REALIGN_CONTROL_NODES. Otherwise, skip this step.
```
=> SELECT REALIGN_CONTROL_NODES();
```
Save cluster changes to the Spread configuration file by calling RELOAD_SPREAD:
```
=> SELECT RELOAD_SPREAD(true);
```
Use Administration tools to restart the database.
Save changes to the cluster's data layout by calling REBALANCE_CLUSTER:
```
=> SELECT REBALANCE_CLUSTER();
```

Creating fault groups

Important

Prerequisites

Run the fault group script

Tip

See also