From 0f39d5050dc0dce99258381f33f1832c437aff85 Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Sun, 23 Oct 2011 00:43:39 -0400
Subject: [PATCH] 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.
---
 src/backend/nodes/outfuncs.c          | 1 +
 src/backend/optimizer/path/indxpath.c | 7 ++++---
 src/backend/optimizer/util/plancat.c  | 6 ++++++
 src/backend/utils/adt/selfuncs.c      | 4 +++-
 src/include/nodes/relation.h          | 1 +
 5 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/src/backend/nodes/outfuncs.c b/src/backend/nodes/outfuncs.c
index 98a02b27ddf..f7d39edf6fd 100644
--- a/src/backend/nodes/outfuncs.c
+++ b/src/backend/nodes/outfuncs.c
@@ -1770,6 +1770,7 @@ _outIndexOptInfo(StringInfo str, IndexOptInfo *node)
 	WRITE_NODE_FIELD(indextlist);
 	WRITE_BOOL_FIELD(predOK);
 	WRITE_BOOL_FIELD(unique);
+	WRITE_BOOL_FIELD(immediate);
 	WRITE_BOOL_FIELD(hypothetical);
 }
 
diff --git a/src/backend/optimizer/path/indxpath.c b/src/backend/optimizer/path/indxpath.c
index 940efb38b66..77df5a24ea2 100644
--- a/src/backend/optimizer/path/indxpath.c
+++ b/src/backend/optimizer/path/indxpath.c
@@ -2277,10 +2277,11 @@ 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;
 
 		/*
diff --git a/src/backend/optimizer/util/plancat.c b/src/backend/optimizer/util/plancat.c
index bb809522424..de629e93c9a 100644
--- a/src/backend/optimizer/util/plancat.c
+++ b/src/backend/optimizer/util/plancat.c
@@ -324,6 +324,7 @@ get_relation_info(PlannerInfo *root, Oid relationObjectId, bool inhparent,
 
 			info->predOK = false;		/* set later in indxpath.c */
 			info->unique = index->indisunique;
+			info->immediate = index->indimmediate;
 			info->hypothetical = false;
 
 			/*
@@ -1076,6 +1077,11 @@ 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)
diff --git a/src/backend/utils/adt/selfuncs.c b/src/backend/utils/adt/selfuncs.c
index 96946281dab..f05cc4f87ee 100644
--- a/src/backend/utils/adt/selfuncs.c
+++ b/src/backend/utils/adt/selfuncs.c
@@ -4129,7 +4129,9 @@ get_join_variables(PlannerInfo *root, List *args, SpecialJoinInfo *sjinfo,
  *		commonly the same as the exposed type of the variable argument,
  *		but can be different in binary-compatible-type cases.
  *	isunique: TRUE if we were able to match the var to a unique index,
- *		implying its values are unique for this query.
+ *		implying its values are unique for this query.  (Caution: this
+ *		should be trusted for statistical purposes only, since we do not
+ *		check indimmediate.)
  *
  * Caller is responsible for doing ReleaseVariableStats() before exiting.
  */
diff --git a/src/include/nodes/relation.h b/src/include/nodes/relation.h
index 2925d7e7659..ede97571e06 100644
--- a/src/include/nodes/relation.h
+++ b/src/include/nodes/relation.h
@@ -488,6 +488,7 @@ typedef struct IndexOptInfo
 
 	bool		predOK;			/* true if predicate matches query */
 	bool		unique;			/* true if a unique index */
+	bool		immediate;		/* is uniqueness enforced immediately? */
 	bool		hypothetical;	/* true if index doesn't really exist */
 	bool		amcanorderbyop; /* does AM support order by operator result? */
 	bool		amcanreturn;	/* can AM return IndexTuples? */
-- 
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