Fix planner failure with extended statistics on partitioned tables.

Some cases would result in "cache lookup failed for statistics object",
due to trying to fetch inherited statistics when only non-inherited
ones are available or vice versa.

Richard Guo and Justin Pryzby

Discussion: https://postgr.es/m/20221030170520.GM16921@telsasoft.com

src/backend/utils/adt/selfuncs.c

@@ -3913,7 +3913,7 @@ estimate_multivariate_ndistinct(PlannerInfo *root, RelOptInfo *rel,
 	Oid			statOid = InvalidOid;
 	MVNDistinct *stats;
 	StatisticExtInfo *matched_info = NULL;
-	RangeTblEntry *rte;
+	RangeTblEntry *rte = planner_rt_fetch(rel->relid, root);
 
 	/* bail out immediately if the table has no extended statistics */
 	if (!rel->statlist)
@@ -3933,6 +3933,10 @@ estimate_multivariate_ndistinct(PlannerInfo *root, RelOptInfo *rel,
 		if (info->kind != STATS_EXT_NDISTINCT)
 			continue;
 
+		/* skip statistics with mismatching stxdinherit value */
+		if (info->inherit != rte->inh)
+			continue;
+
 		/*
 		 * Determine how many expressions (and variables in non-matched
 		 * expressions) match. We'll then use these numbers to pick the
@@ -4004,7 +4008,6 @@ estimate_multivariate_ndistinct(PlannerInfo *root, RelOptInfo *rel,
 
 	Assert(nmatches_vars + nmatches_exprs > 1);
 
-	rte = planner_rt_fetch(rel->relid, root);
 	stats = statext_ndistinct_load(statOid, rte->inh);
 
 	/*
@@ -5241,6 +5244,10 @@ examine_variable(PlannerInfo *root, Node *node, int varRelid,
 			if (info->kind != STATS_EXT_EXPRESSIONS)
 				continue;
 
+			/* skip stats with mismatching stxdinherit value */
+			if (info->inherit != rte->inh)
+				continue;
+
 			pos = 0;
 			foreach(expr_item, info->exprs)
 			{

src/test/regress/expected/stats_ext.out

@@ -232,7 +232,7 @@ DROP TABLE stxdinh, stxdinh1, stxdinh2;
 CREATE TABLE stxdinp(i int, a int, b int) PARTITION BY RANGE (i);
 CREATE TABLE stxdinp1 PARTITION OF stxdinp FOR VALUES FROM (1) TO (100);
 INSERT INTO stxdinp SELECT 1, a/100, a/100 FROM generate_series(1, 999) a;
-CREATE STATISTICS stxdinp ON a, b FROM stxdinp;
+CREATE STATISTICS stxdinp ON (a + 1), a, b FROM stxdinp;
 VACUUM ANALYZE stxdinp; -- partitions are processed recursively
 SELECT 1 FROM pg_statistic_ext WHERE stxrelid = 'stxdinp'::regclass;
  ?column? 
@@ -246,6 +246,12 @@ SELECT * FROM check_estimated_rows('SELECT a, b FROM stxdinp GROUP BY 1, 2');
         10 |     10
 (1 row)
 
+SELECT * FROM check_estimated_rows('SELECT a + 1, b FROM ONLY stxdinp GROUP BY 1, 2');
+ estimated | actual 
+-----------+--------
+         1 |      0
+(1 row)
+
 DROP TABLE stxdinp;
 -- basic test for statistics on expressions
 CREATE TABLE ab1 (a INTEGER, b INTEGER, c TIMESTAMP, d TIMESTAMPTZ);

src/test/regress/sql/stats_ext.sql

@@ -139,10 +139,11 @@ DROP TABLE stxdinh, stxdinh1, stxdinh2;
 CREATE TABLE stxdinp(i int, a int, b int) PARTITION BY RANGE (i);
 CREATE TABLE stxdinp1 PARTITION OF stxdinp FOR VALUES FROM (1) TO (100);
 INSERT INTO stxdinp SELECT 1, a/100, a/100 FROM generate_series(1, 999) a;
-CREATE STATISTICS stxdinp ON a, b FROM stxdinp;
+CREATE STATISTICS stxdinp ON (a + 1), a, b FROM stxdinp;
 VACUUM ANALYZE stxdinp; -- partitions are processed recursively
 SELECT 1 FROM pg_statistic_ext WHERE stxrelid = 'stxdinp'::regclass;
 SELECT * FROM check_estimated_rows('SELECT a, b FROM stxdinp GROUP BY 1, 2');
+SELECT * FROM check_estimated_rows('SELECT a + 1, b FROM ONLY stxdinp GROUP BY 1, 2');
 DROP TABLE stxdinp;
 
 -- basic test for statistics on expressions