A newer version of this documentation is available. Click here to view the most up-to-date release of the Greenplum 4.x documentation.
When Pivotal Query Optimizer (PQO) is enabled, optimizer_parallel_union controls the amount of parallelization that occurs for queries that contain a UNION or UNION ALL clause.
When the value is off, the default, PQO generates a query plan where each child of an APPEND(UNION) operator is in the same slice as the APPEND operator. During query execution, the children are executed in a sequential manner.
When the value is on, PQO generates a query plan where a redistribution motion node is under an APPEND(UNION) operator. During query execution, the children and the parent APPEND operator are on different slices, allowing the children of the APPEND(UNION) operator to execute in parallel on segment instances.
The parameter can be set for a database system, an individual database, or a session or query.
|Value Range||Default||Set Classifications|