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Commitbc397e5

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De-dupicate Memoize cache keys
It was possible when determining the cache keys for a Memoize path thatif the same expr appeared twice in the parameterized path's ppi_clausesand/or in the Nested Loop's inner relation's lateral_vars.  If thishappened the Memoize node's cache keys would contain duplicates.  Thisisn't a problem for correctness, all it means is that the cache lookupswill be suboptimal due to having redundant work to do on every hash tablelookup and insert.Here we adjust paraminfo_get_equal_hashops() to look for duplicates andignore them when we find them.Author: David RowleyReviewed-by: Richard GuoDiscussion:https://postgr.es/m/422277.1706207562%40sss.pgh.pa.us
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+21
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2 files changed

+21
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‎src/backend/optimizer/path/joinpath.c

Lines changed: 20 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -492,8 +492,16 @@ paraminfo_get_equal_hashops(PlannerInfo *root, ParamPathInfo *param_info,
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return false;
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}
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495-
*operators=lappend_oid(*operators,hasheqoperator);
496-
*param_exprs=lappend(*param_exprs,expr);
495+
/*
496+
* 'expr' may already exist as a parameter from a previous item in
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* ppi_clauses. No need to include it again, however we'd better
498+
* ensure we do switch into binary mode if required. See below.
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*/
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if (!list_member(*param_exprs,expr))
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{
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*operators=lappend_oid(*operators,hasheqoperator);
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*param_exprs=lappend(*param_exprs,expr);
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}
497505

498506
/*
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* When the join operator is not hashable then it's possible that
@@ -536,8 +544,16 @@ paraminfo_get_equal_hashops(PlannerInfo *root, ParamPathInfo *param_info,
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return false;
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}
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539-
*operators=lappend_oid(*operators,typentry->eq_opr);
540-
*param_exprs=lappend(*param_exprs,expr);
547+
/*
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* 'expr' may already exist as a parameter from the ppi_clauses. No
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* need to include it again, however we'd better ensure we do switch
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* into binary mode.
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*/
552+
if (!list_member(*param_exprs,expr))
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{
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*operators=lappend_oid(*operators,typentry->eq_opr);
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*param_exprs=lappend(*param_exprs,expr);
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}
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542558
/*
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* We must go into binary mode as we don't have too much of an idea of

‎src/test/regress/expected/memoize.out

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -107,7 +107,7 @@ WHERE t1.unique1 < 10;', false);
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-> Index Scan using tenk1_unique1 on tenk1 t1 (actual rows=10 loops=N)
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Index Cond: (unique1 < 10)
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-> Memoize (actual rows=2 loops=N)
110-
Cache Key: t1.two, t1.two
110+
Cache Key: t1.two
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Cache Mode: binary
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Hits: 8 Misses: 2 Evictions: Zero Overflows: 0 Memory Usage: NkB
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-> Subquery Scan on t2 (actual rows=2 loops=N)

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