GPORCA Limitations
- Unsupported SQL Query Features
- Performance Regressions

GPORCA Limitations

There are limitations in HAWQ when GPORCA is enabled. GPORCA and the legacy query optimizer currently coexist in HAWQ because GPORCA does not support all HAWQ features.

Unsupported SQL Query Features

These HAWQ features are unsupported when GPORCA is enabled:

Indexed expressions
PERCENTILE window function
External parameters
SortMergeJoin (SMJ)
Ordered aggregations
These analytics extensions:
- CUBE
- Multiple grouping sets
These scalar operators:
- ROW
- ROWCOMPARE
- FIELDSELECT
Multiple DISTINCT qualified aggregate functions
Inverse distribution functions

Performance Regressions

When GPORCA is enabled in HAWQ, the following features are known performance regressions:

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 legacy 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.