8000 Don't trust deferred-unique indexes for join removal. · fschopp/postgres@0f39d50 · GitHub 8000
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Don't trust deferred-unique indexes for join removal.
The uniqueness condition might fail to hold intra-transaction, and assuming it does can give incorrect query results. Per report from Marti Raudsepp, though this is not his proposed patch. Back-patch to 9.0, where both these features were introduced. In the released branches, add the new IndexOptInfo field to the end of the struct, to try to minimize ABI breakage for third-party code that may be examining that struct.
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‎src/backend/nodes/outfuncs.c‎

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@@ -1770,6 +1770,7 @@ _outIndexOptInfo(StringInfo str, IndexOptInfo *node)
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WRITE_NODE_FIELD(indextlist);
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WRITE_BOOL_FIELD(predOK);
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WRITE_BOOL_FIELD(unique);
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WRITE_BOOL_FIELD(immediate);
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WRITE_BOOL_FIELD(hypothetical);
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}
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‎src/backend/optimizer/path/indxpath.c‎

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@@ -2277,10 +2277,11 @@ relation_has_unique_index_for(PlannerInfo *root, RelOptInfo *rel,
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int c;
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/*
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* If the index is not unique or if it's a partial index that doesn't
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* match the query, it's useless here.
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* If the index is not unique, or not immediately enforced, or if it's
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* a partial index that doesn't match the query, it's useless here.
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*/
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if (!ind->unique || (ind->indpred != NIL && !ind->predOK))
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if (!ind->unique || !ind->immediate ||
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(ind->indpred != NIL && !ind->predOK))
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continue;
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/*

‎src/backend/optimizer/util/plancat.c‎

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@@ -324,6 +324,7 @@ get_relation_info(PlannerInfo *root, Oid relationObjectId, bool inhparent,
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info->predOK = false; /* set later in indxpath.c */
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info->unique = index->indisunique;
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info->immediate = index->indimmediate;
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info->hypothetical = false;
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/*
@@ -1076,6 +1077,11 @@ join_selectivity(PlannerInfo *root,
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* Detect whether there is a unique index on the specified attribute
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* of the specified relation, thus allowing us to conclude that all
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* the (non-null) values of the attribute are distinct.
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*
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* This function does not check the index's indimmediate property, which
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* means that uniqueness may transiently fail to hold intra-transaction.
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* That's appropriate when we are making statistical estimates, but beware
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* of using this for any correctness proofs.
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*/
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bool
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has_unique_index(RelOptInfo *rel, AttrNumber attno)

‎src/backend/utils/adt/selfuncs.c‎

Lines changed: 3 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -4129,7 +4129,9 @@ get_join_variables(PlannerInfo *root, List *args, SpecialJoinInfo *sjinfo,
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* commonly the same as the exposed type of the variable argument,
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* but can be different in binary-compatible-type cases.
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* isunique: TRUE if we were able to match the var to a unique index,
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* implying its values are unique for this query.
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* implying its values are unique for this query. (Caution: this
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* should be trusted for statistical purposes only, since we do not
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* check indimmediate.)
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*
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* Caller is responsible for doing ReleaseVariableStats() before exiting.
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*/

‎src/include/nodes/relation.h‎

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Original file line numberDiff line numberDiff line change
@@ -488,6 +488,7 @@ typedef struct IndexOptInfo
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bool predOK; /* true if predicate matches query */
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bool unique; /* true if a unique index */
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bool immediate; /* is uniqueness enforced immediately? */
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bool hypothetical; /* true if index doesn't really exist */
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bool amcanorderbyop; /* does AM support order by operator result? */
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bool amcanreturn; /* can AM return IndexTuples? */

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