mirror of https://github.com/citusdata/citus.git
766f340ce0
Comment from the code is clear on this: /* * The statistics objects of the distributed table are not relevant * for the distributed planning, so we can override it. * * Normally, we should not need this. However, the combination of * Postgres commit 269b532aef55a579ae02a3e8e8df14101570dfd9 and * Citus function AdjustPartitioningForDistributedPlanning() * forces us to do this. The commit expects statistics objects * of partitions to have "inh" flag set properly. Whereas, the * function overrides "inh" flag. To avoid Postgres to throw error, * we override statlist such that Postgres does not try to process * any statistics objects during the standard_planner() on the * coordinator. In the end, we do not need the standard_planner() * on the coordinator to generate an optimized plan. We call * into standard_planner() for other purposes, such as generating the * relationRestrictionContext here. * * AdjustPartitioningForDistributedPlanning() is a hack that we use * to prevent Postgres' standard_planner() to expand all the partitions * for the distributed planning when a distributed partitioned table * is queried. It is required for both correctness and performance * reasons. Although we can eliminate the use of the function for * the correctness (e.g., make sure that rest of the planner can handle * partitions), it's performance implication is hard to avoid. Certain * planning logic of Citus (such as router or query pushdown) relies * heavily on the relationRestrictionList. If * AdjustPartitioningForDistributedPlanning() is removed, all the * partitions show up in the, causing high planning times for * such queries. */ |
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