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Correct shared hash table rows estimation #263

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Merged
my-ship-it merged 1 commit into from
Nov 3, 2023
Merged

Correct shared hash table rows estimation #263

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25 changes: 1 addition & 24 deletions src/backend/optimizer/path/costsize.c
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Original file line number Diff line number Diff line change
Expand Up @@ -4075,30 +4075,7 @@ initial_cost_hashjoin(PlannerInfo *root, JoinCostWorkspace *workspace,
* number, so we need to undo the division.
*/
if (parallel_hash)
{
/*
* GPDB
* For GP style parallel, inner path's locus could be ReplicatedWorkers.
*
* Join
* / \
* Outer ParallelHash
* \
* ParallelBroadcastMotion
* \
* origin_inner
*
* In this case, inner_path.rows has already taken parallel into account.
* We shouldn't plus parallel_divisor again, else the estimation of Hash
* Table will be much more than the size it really is.
* The side-effect will lead to:
* 1. Estimate or allocate much more memory for shared Hash Table.
* 2. Use MergeJoin instead of HashJoin if planner recognize inner table
* is too big.
*/
if(!CdbPathLocus_IsReplicatedWorkers(inner_path->locus))
inner_path_rows_total *= get_parallel_divisor(inner_path);
}
inner_path_rows_total *= get_parallel_divisor(inner_path);

/*
* Get hash table size that executor would use for inner relation.
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