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| title: GPORCA Limitations |
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| <span class="shortdesc">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. </span> |
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| ## Unsupported SQL Query Features<a id="topic_kgn_vxl_vp"></a> |
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| These HAWQ features are unsupported when GPORCA is enabled: |
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| - 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 |
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| ## Performance Regressions<a id="topic_u4t_vxl_vp"></a> |
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| When GPORCA is enabled in HAWQ, the following features are known performance regressions: |
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| - 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. |
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| Also, enhanced functionality of the features from previous versions could result in additional time required when GPORCA executes SQL statements with the features. |
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