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Commit9529b1e

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Fix hash join when inner hashkey expressions contain Params.
If the inner-side expressions contain PARAM_EXEC Params, we mustre-hash whenever the values of those Params change. The executormechanism for that exists already, but we failed to invoke it becausefinalize_plan() neglected to search the Hash.hashkeys field forParams. This allowed a previous scan's hash table to be re-usedwhen it should not be, leading to rows missing from the join's output.(I believe incorrectly-included join rows are impossible however,since checking the real hashclauses would reject false matches.)This bug is very ancient, dating probably tod24d75f of 7.4.Sadly, this simple fix depends on the plan representational changesmade by2abd7ae, so it will only work back to v12. I thoughtabout trying to make some kind of hack for v11, but I'm leeryof putting code significantly different from what is used in thenewer branches into a nearly-EOL branch. Seeing that the bugescaped detection for a full twenty years, problematic casesmust be rare; so I don't feel too awful about leaving v11 as-is.Per bug #17985 from Zuming Jiang. Back-patch to v12.Discussion:https://postgr.es/m/17985-748b66607acd432e@postgresql.org
1 parentdcef5b0 commit9529b1e

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3 files changed

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3 files changed

+60
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lines changed

‎src/backend/optimizer/plan/subselect.c

Lines changed: 5 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -2630,6 +2630,11 @@ finalize_plan(PlannerInfo *root, Plan *plan,
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&context);
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break;
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caseT_Hash:
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finalize_primnode((Node*) ((Hash*)plan)->hashkeys,
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&context);
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break;
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caseT_Limit:
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finalize_primnode(((Limit*)plan)->limitOffset,
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&context);
@@ -2725,7 +2730,6 @@ finalize_plan(PlannerInfo *root, Plan *plan,
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break;
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caseT_ProjectSet:
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caseT_Hash:
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caseT_Material:
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caseT_Sort:
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caseT_Unique:

‎src/test/regress/expected/join_hash.out

Lines changed: 36 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1013,3 +1013,39 @@ WHERE
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(1 row)
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ROLLBACK;
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-- Verify that we behave sanely when the inner hash keys contain parameters
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-- (that is, outer or lateral references). This situation has to defeat
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-- re-use of the inner hash table across rescans.
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begin;
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set local enable_hashjoin = on;
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explain (costs off)
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select i8.q2, ss.* from
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int8_tbl i8,
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lateral (select t1.fivethous, i4.f1 from tenk1 t1 join int4_tbl i4
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on t1.fivethous = i4.f1+i8.q2 order by 1,2) ss;
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QUERY PLAN
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-----------------------------------------------------------
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Nested Loop
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-> Seq Scan on int8_tbl i8
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-> Sort
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Sort Key: t1.fivethous, i4.f1
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-> Hash Join
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Hash Cond: (t1.fivethous = (i4.f1 + i8.q2))
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-> Seq Scan on tenk1 t1
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-> Hash
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-> Seq Scan on int4_tbl i4
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(9 rows)
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select i8.q2, ss.* from
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int8_tbl i8,
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lateral (select t1.fivethous, i4.f1 from tenk1 t1 join int4_tbl i4
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on t1.fivethous = i4.f1+i8.q2 order by 1,2) ss;
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q2 | fivethous | f1
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-----+-----------+----
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456 | 456 | 0
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456 | 456 | 0
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123 | 123 | 0
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123 | 123 | 0
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(4 rows)
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rollback;

‎src/test/regress/sql/join_hash.sql

Lines changed: 19 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -538,3 +538,22 @@ WHERE
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ANDhjtest_1.a<>hjtest_2.b;
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ROLLBACK;
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-- Verify that we behave sanely when the inner hash keys contain parameters
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-- (that is, outer or lateral references). This situation has to defeat
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-- re-use of the inner hash table across rescans.
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begin;
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set local enable_hashjoin=on;
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explain (costs off)
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selecti8.q2, ss.*from
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int8_tbl i8,
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lateral (selectt1.fivethous,i4.f1from tenk1 t1join int4_tbl i4
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ont1.fivethous=i4.f1+i8.q2order by1,2) ss;
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selecti8.q2, ss.*from
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int8_tbl i8,
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lateral (selectt1.fivethous,i4.f1from tenk1 t1join int4_tbl i4
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ont1.fivethous=i4.f1+i8.q2order by1,2) ss;
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rollback;

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