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Don't trust deferred-unique indexes for join removal.

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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.
This commit is contained in:
Tom Lane
2011-10-23 00:43:52 -04:00
parent 015cda44cf
commit 9fbb3edff0
5 changed files with 16 additions and 4 deletions
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7
src/backend/optimizer/path/indxpath.c
View File

@ -1948,10 +1948,11 @@ relation_has_unique_index_for(PlannerInfo *root, RelOptInfo *rel,
int c;
/*
* If the index is not unique or if it's a partial index that doesn't
* match the query, it's useless here.
* If the index is not unique, or not immediately enforced, or if it's
* a partial index that doesn't match the query, it's useless here.
*/
if (!ind->unique || (ind->indpred != NIL && !ind->predOK))
if (!ind->unique || !ind->immediate ||
(ind->indpred != NIL && !ind->predOK))
continue;
/*

6
src/backend/optimizer/util/plancat.c
View File

@ -275,6 +275,7 @@ get_relation_info(PlannerInfo *root, Oid relationObjectId, bool inhparent,
ChangeVarNodes((Node *) info->indpred, 1, varno, 0);
info->predOK = false; /* set later in indxpath.c */
info->unique = index->indisunique;
info->immediate = index->indimmediate;
info->hypothetical = false;
/*
@ -876,6 +877,11 @@ join_selectivity(PlannerInfo *root,
* Detect whether there is a unique index on the specified attribute
* of the specified relation, thus allowing us to conclude that all
* the (non-null) values of the attribute are distinct.
*
* This function does not check the index's indimmediate property, which
* means that uniqueness may transiently fail to hold intra-transaction.
* That's appropriate when we are making statistical estimates, but beware
* of using this for any correctness proofs.
*/
bool
has_unique_index(RelOptInfo *rel, AttrNumber attno)