database/postgres
1
0
Fork 0
mirror of https://github.com/postgres/postgres.git synced 2025-09-02 04:21:28 +03:00
Code Activity

Support "Right Semi Join" plan shapes

Browse Source 
Hash joins can support semijoin with the LHS input on the right, using
the existing logic for inner join, combined with the assurance that only
the first match for each inner tuple is considered, which can be
achieved by leveraging the HEAP_TUPLE_HAS_MATCH flag.  This can be very
useful in some cases since we may now have the option to hash the
smaller table instead of the larger.

Merge join could likely support "Right Semi Join" too.  However, the
benefit of swapping inputs tends to be small here, so we do not address
that in this patch.

Note that this patch also modifies a test query in join.sql to ensure it
continues testing as intended.  With this patch the original query would
result in a right-semi-join rather than semi-join, compromising its
original purpose of testing the fix for neqjoinsel's behavior for
semi-joins.

Author: Richard Guo
Reviewed-by: wenhui qiu, Alena Rybakina, Japin Li
Discussion: https://postgr.es/m/CAMbWs4_X1mN=ic+SxcyymUqFx9bB8pqSLTGJ-F=MHy4PW3eRXw@mail.gmail.com
This commit is contained in:
Richard Guo
2024-07-05 09:26:48 +09:00
parent 5a519abedd
commit aa86129e19
14 changed files with 222 additions and 173 deletions
Download Patch File Download Diff File Expand all files Collapse all files

15
src/backend/executor/nodeHashjoin.c
View File

@@ -533,6 +533,14 @@ ExecHashJoinImpl(PlanState *pstate, bool parallel)
}
}
/*
* In a right-semijoin, we only need the first match for each
* inner tuple.
*/
if (node->js.jointype == JOIN_RIGHT_SEMI &&
HeapTupleHeaderHasMatch(HJTUPLE_MINTUPLE(node->hj_CurTuple)))
continue;
/*
* We've got a match, but still need to test non-hashed quals.
* ExecScanHashBucket already set up all the state needed to
@@ -549,10 +557,10 @@ ExecHashJoinImpl(PlanState *pstate, bool parallel)
{
node->hj_MatchedOuter = true;
/*
* This is really only needed if HJ_FILL_INNER(node), but
* we'll avoid the branch and just set it always.
* This is really only needed if HJ_FILL_INNER(node) or if
* we are in a right-semijoin, but we'll avoid the branch
* and just set it always.
*/
if (!HeapTupleHeaderHasMatch(HJTUPLE_MINTUPLE(node->hj_CurTuple)))
HeapTupleHeaderSetMatch(HJTUPLE_MINTUPLE(node->hj_CurTuple));
@@ -779,6 +787,7 @@ ExecInitHashJoin(HashJoin *node, EState *estate, int eflags)
{
case JOIN_INNER:
case JOIN_SEMI:
case JOIN_RIGHT_SEMI:
break;
case JOIN_LEFT:
case JOIN_ANTI: