Teach the planner to treat a partial unique index as proving a variable is

unique for a particular query, if the index predicate is satisfied.  This
requires a bit of reordering of operations so that we check the predicates
before doing any selectivity estimates, but shouldn't really cause any
noticeable slowdown.  Per a comment from Michal Politowski.

3 files changed, 23 insertions, 10 deletions

diff --git a/src/backend/optimizer/path/allpaths.c b/src/backend/optimizer/path/allpaths.c
index b94b8a5811..4e0d9ca4e5 100644
--- a/src/backend/optimizer/path/allpaths.c
+++ b/src/backend/optimizer/path/allpaths.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/optimizer/path/allpaths.c,v 1.179 2009/01/01 17:23:43 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/optimizer/path/allpaths.c,v 1.180 2009/02/15 20:16:21 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -225,19 +225,25 @@ set_plain_rel_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte)
 		return;
 	}
 
+	/*
+	 * Test any partial indexes of rel for applicability.  We must do this
+	 * first since partial unique indexes can affect size estimates.
+	 */
+	check_partial_indexes(root, rel);
+
 	/* Mark rel with estimated output rows, width, etc */
 	set_baserel_size_estimates(root, rel);
 
-	/* Test any partial indexes of rel for applicability */
-	check_partial_indexes(root, rel);
-
 	/*
 	 * Check to see if we can extract any restriction conditions from join
 	 * quals that are OR-of-AND structures.  If so, add them to the rel's
-	 * restriction list, and recompute the size estimates.
+	 * restriction list, and redo the above steps.
 	 */
 	if (create_or_index_quals(root, rel))
+	{
+		check_partial_indexes(root, rel);
 		set_baserel_size_estimates(root, rel);
+	}
 
 	/*
 	 * Generate paths and add them to the rel's pathlist.
diff --git a/src/backend/optimizer/path/indxpath.c b/src/backend/optimizer/path/indxpath.c
index b3482b4b5b..6f27a19182 100644
--- a/src/backend/optimizer/path/indxpath.c
+++ b/src/backend/optimizer/path/indxpath.c
@@ -9,7 +9,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/optimizer/path/indxpath.c,v 1.235 2009/01/01 17:23:43 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/optimizer/path/indxpath.c,v 1.236 2009/02/15 20:16:21 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1367,8 +1367,12 @@ match_rowcompare_to_indexcol(IndexOptInfo *index,
 
 /*
  * check_partial_indexes
- *		Check each partial index of the relation, and mark it predOK or not
- *		depending on whether the predicate is satisfied for this query.
+ *		Check each partial index of the relation, and mark it predOK if
+ *		the index's predicate is satisfied for this query.
+ *
+ * Note: it is possible for this to get re-run after adding more restrictions
+ * to the rel; so we might be able to prove more indexes OK.  We assume that
+ * adding more restrictions can't make an index not OK.
  */
 void
 check_partial_indexes(PlannerInfo *root, RelOptInfo *rel)
@@ -1383,6 +1387,9 @@ check_partial_indexes(PlannerInfo *root, RelOptInfo *rel)
 		if (index->indpred == NIL)
 			continue;			/* ignore non-partial indexes */
 
+		if (index->predOK)
+			continue;			/* don't repeat work if already proven OK */
+
 		index->predOK = predicate_implied_by(index->indpred,
 											 restrictinfo_list);
 	}
diff --git a/src/backend/optimizer/path/orindxpath.c b/src/backend/optimizer/path/orindxpath.c
index 638078e169..2f8a67394e 100644
--- a/src/backend/optimizer/path/orindxpath.c
+++ b/src/backend/optimizer/path/orindxpath.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/optimizer/path/orindxpath.c,v 1.87 2009/02/06 23:43:23 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/optimizer/path/orindxpath.c,v 1.88 2009/02/15 20:16:21 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -181,6 +181,6 @@ create_or_index_quals(PlannerInfo *root, RelOptInfo *rel)
 		/* It isn't an outer join clause, so no need to adjust outer_selec */
 	}
 
-	/* Tell caller to recompute rel's rows estimate */
+	/* Tell caller to recompute partial index status and rowcount estimate */
 	return true;
 }