GPORCA Limitations
There are limitations in Greenplum Database when using the default GPORCA optimizer.
GPORCA and the Postgres query optimizer currently coexist in Greenplum Database because GPORCA
does not support all Greenplum Database features.
This section describes the limitations.
Unsupported SQL Query Features
Certain query features are not supported with the default GPORCA optimizer. When an
unsupported query is executed, Greenplum logs this notice along with the query
text:Feature not supported by the Pivotal Query Optimizer: UTILITY command
These features are unsupported when GPORCA is enabled (the default):
- Indexed expressions (an index defined as expression based on one or more columns of
the table)
- GIN indexing method. GPORCA supports only B-tree, bitmap, and GiST indexes. GPORCA
ignores indexes created with unsupported methods.
- External parameters
- These types of partitioned tables:
- Non-uniform partitioned tables.
- Partitioned tables that have been altered to use an external table as a leaf child
partition.
- SortMergeJoin (SMJ).
- Ordered aggregations.
- These analytics extensions:
- CUBE
- Multiple grouping sets
- These scalar operators:
- ROW
- ROWCOMPARE
- FIELDSELECT
- Aggregate functions that take set operators as input arguments.
- percentile_* window functions (Greenplum Database does not support
ordered-set aggregate functions).
- Inverse distribution functions.
- Queries that execute functions that are defined with the ON MASTER or
ON ALL SEGMENTS attribute.
- Queries that contain UNICODE characters in metadata names, such as table names, and
the characters are not compatible with the host system locale.
- SELECT, UPDATE, and DELETE commands
where a table name is qualified by the ONLY keyword.
- Per-column collation. GPORCA supports collation only when all columns in the query use
the same collation. If columns in the query use different collations, then Greenplum
uses the Postgres query planner.
Performance Regressions
The following features are known performance regressions that occur with GPORCA enabled:
- Short running queries - For GPORCA, short running queries might encounter additional
overhead due to GPORCA enhancements for determining an optimal query execution
plan.
- ANALYZE - For GPORCA, the ANALYZE command
generates root partition statistics for partitioned tables. For the Postgres optimizer,
these statistics are not generated.
- DML operations - For GPORCA, DML enhancements including the support of updates on
partition and distribution keys might require additional overhead.
Also, enhanced functionality of the features from previous versions could result in
additional time required when GPORCA executes SQL statements with the features.