From 427c6b5b984928972e955f4477c6ba64edbb66cc Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Tue, 2 May 2006 04:34:18 +0000
Subject: [PATCH] Avoid assuming that statistics for a parent relation reflect
 the properties of the union of its child relations as well.  This might have
 been a good idea when it was originally coded, but it's a fatally bad idea
 when inheritance is being used for partitioning.  It's better to have no
 stats at all than completely misleading stats.  Per report from Mark
 Liberman.

The bug arguably exists all the way back, but I've only patched HEAD and 8.1
because we weren't particularly trying to support partitioning before 8.1.

Eventually we ought to look at deriving union statistics instead of just
punting, but for now the drop kick looks good.
---
 src/backend/optimizer/path/allpaths.c |  9 ++++++++-
 src/backend/utils/adt/selfuncs.c      | 18 +++++++++++++-----
 2 files changed, 21 insertions(+), 6 deletions(-)

diff --git a/src/backend/optimizer/path/allpaths.c b/src/backend/optimizer/path/allpaths.c
index f35e87962d..de82c3df8d 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 1.145 2006/04/30 18:30:39 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/optimizer/path/allpaths.c,v 1.146 2006/05/02 04:34:18 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -273,6 +273,13 @@ set_append_rel_pathlist(PlannerInfo *root, RelOptInfo *rel,
 				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 				 errmsg("SELECT FOR UPDATE/SHARE is not supported for inheritance queries")));
 
+	/*
+	 * We might have looked up indexes for the parent rel, but they're
+	 * really not relevant to the appendrel.  Reset the pointer to avoid
+	 * any confusion.
+	 */
+	rel->indexlist = NIL;
+
 	/*
 	 * Initialize to compute size estimates for whole append relation
 	 */
diff --git a/src/backend/utils/adt/selfuncs.c b/src/backend/utils/adt/selfuncs.c
index 082089b9f1..5f830ef0cd 100644
--- a/src/backend/utils/adt/selfuncs.c
+++ b/src/backend/utils/adt/selfuncs.c
@@ -15,7 +15,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/utils/adt/selfuncs.c,v 1.203 2006/04/27 17:52:40 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/utils/adt/selfuncs.c,v 1.204 2006/05/02 04:34:18 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -3265,19 +3265,27 @@ examine_variable(PlannerInfo *root, Node *node, int varRelid,
 		(varRelid == 0 || varRelid == ((Var *) basenode)->varno))
 	{
 		Var		   *var = (Var *) basenode;
-		Oid			relid;
+		RangeTblEntry *rte;
 
 		vardata->var = basenode;	/* return Var without relabeling */
 		vardata->rel = find_base_rel(root, var->varno);
 		vardata->atttype = var->vartype;
 		vardata->atttypmod = var->vartypmod;
 
-		relid = getrelid(var->varno, root->parse->rtable);
+		rte = rt_fetch(var->varno, root->parse->rtable);
 
-		if (OidIsValid(relid))
+		if (rte->inh)
+		{
+			/*
+			 * XXX This means the Var represents a column of an append relation.
+			 * Later add code to look at the member relations and try to derive
+			 * some kind of combined statistics?
+			 */
+		}
+		else if (rte->rtekind == RTE_RELATION)
 		{
 			vardata->statsTuple = SearchSysCache(STATRELATT,
-												 ObjectIdGetDatum(relid),
+												 ObjectIdGetDatum(rte->relid),
 												 Int16GetDatum(var->varattno),
 												 0, 0);
 		}