Build inherited extended stats on partitioned tables

Commit 859b3003de disabled building of extended stats for inheritance
trees, to prevent updating the same catalog row twice. While that
resolved the issue, it also means there are no extended stats for
declaratively partitioned tables, because there are no data in the
non-leaf relations.

That also means declaratively partitioned tables were not affected by
the issue 859b3003de addressed, which means this is a regression
affecting queries that calculate estimates for the whole inheritance
tree as a whole (which includes e.g. GROUP BY queries).

But because partitioned tables are empty, we can invert the condition
and build statistics only for the case with inheritance, without losing
anything. And we can consider them when calculating estimates.

It may be necessary to run ANALYZE on partitioned tables, to collect
proper statistics. For declarative partitioning there should no prior
statistics, and it might take time before autoanalyze is triggered. For
tables partitioned by inheritance the statistics may include data from
child relations (if built 859b3003de), contradicting the current code.

Report and patch by Justin Pryzby, minor fixes and cleanup by me.
Backpatch all the way back to PostgreSQL 10, where extended statistics
were introduced (same as 859b3003de).

Author: Justin Pryzby
Reported-by: Justin Pryzby
Backpatch-through: 10
Discussion: https://postgr.es/m/20210923212624.GI831%40telsasoft.com

diff --git a/src/backend/commands/analyze.c b/src/backend/commands/analyze.c
index 37b77e28cb9abdf5fccdaf2ef96a1d494f7ede39..26169808beec15e6f07959482f017b15aa85e75c 100644 (file)
--- a/src/backend/commands/analyze.c
+++ b/src/backend/commands/analyze.c
@@ -529,6 +529,7 @@ do_analyze_rel(Relation onerel, int options, VacuumParams *params,
    {
        MemoryContext col_context,
                    old_context;
+       bool        build_ext_stats;
 
        col_context = AllocSetContextCreate(anl_context,
                                            "Analyze Column",
@@ -589,13 +590,28 @@ do_analyze_rel(Relation onerel, int options, VacuumParams *params,
                            thisdata->attr_cnt, thisdata->vacattrstats);
        }
 
+       /*
+        * Should we build extended statistics for this relation?
+        *
+        * The extended statistics catalog does not include an inheritance
+        * flag, so we can't store statistics built both with and without
+        * data from child relations. We can store just one set of statistics
+        * per relation. For plain relations that's fine, but for inheritance
+        * trees we have to pick whether to store statistics for just the
+        * one relation or the whole tree. For plain inheritance we store
+        * the (!inh) version, mostly for backwards compatibility reasons.
+        * For partitioned tables that's pointless (the non-leaf tables are
+        * always empty), so we store stats representing the whole tree.
+        */
+       build_ext_stats = (onerel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE) ? inh : (!inh);
+
        /*
         * Build extended statistics (if there are any).
         *
         * For now we only build extended statistics on individual relations,
         * not for relations representing inheritance trees.
         */
-       if (!inh)
+       if (build_ext_stats)
            BuildRelationExtStatistics(onerel, totalrows, numrows, rows,
                                       attr_cnt, vacattrstats);
    }

diff --git a/src/backend/statistics/dependencies.c b/src/backend/statistics/dependencies.c
index 9c7e7d9bfde0a2bbcd6a33616ab93db1d3e0f4a2..2ed80dce3c20bafe2cae6306c2446ffa00dc6942 100644 (file)
--- a/src/backend/statistics/dependencies.c
+++ b/src/backend/statistics/dependencies.c
@@ -15,6 +15,7 @@
 
 #include "access/htup_details.h"
 #include "access/sysattr.h"
+#include "catalog/pg_class.h"
 #include "catalog/pg_operator.h"
 #include "catalog/pg_statistic_ext.h"
 #include "lib/stringinfo.h"
@@ -968,10 +969,13 @@ dependencies_clauselist_selectivity(PlannerInfo *root,
    *estimatedclauses = NULL;
 
    /*
-    * When dealing with inheritance trees, ignore extended stats (which were
-    * built without data from child rels, and thus do not represent them).
+    * When dealing with regular inheritance trees, ignore extended stats
+    * (which were built without data from child rels, and thus do not
+    * represent them). For partitioned tables data there's no data in the
+    * non-leaf relations, so we build stats only for the inheritance tree.
+    * So for partitioned tables we do consider extended stats.
     */
-   if (rte->inh)
+   if (rte->inh && rte->relkind != RELKIND_PARTITIONED_TABLE)
        return 1.0;
 
    /* check if there's any stats that might be useful for us. */

diff --git a/src/backend/utils/adt/selfuncs.c b/src/backend/utils/adt/selfuncs.c
index af247043f45601264368d559af36e33f42afc521..962bf075eea6be5f9d0743fcece4c514a3aff55c 100644 (file)
--- a/src/backend/utils/adt/selfuncs.c
+++ b/src/backend/utils/adt/selfuncs.c
@@ -3749,19 +3749,23 @@ estimate_multivariate_ndistinct(PlannerInfo *root, RelOptInfo *rel,
    Oid         statOid = InvalidOid;
    MVNDistinct *stats;
    Bitmapset  *matched = NULL;
-   RangeTblEntry       *rte = planner_rt_fetch(rel->relid, root);
-
-   /*
-    * When dealing with inheritance trees, ignore extended stats (which were
-    * built without data from child rels, and thus do not represent them).
-    */
-   if (rte->inh)
-       return false;
+   RangeTblEntry       *rte;
 
    /* bail out immediately if the table has no extended statistics */
    if (!rel->statlist)
        return false;
 
+   /*
+    * When dealing with regular inheritance trees, ignore extended stats
+    * (which were built without data from child rels, and thus do not
+    * represent them). For partitioned tables data there's no data in the
+    * non-leaf relations, so we build stats only for the inheritance tree.
+    * So for partitioned tables we do consider extended stats.
+    */
+   rte = planner_rt_fetch(rel->relid, root);
+   if (rte->inh && rte->relkind != RELKIND_PARTITIONED_TABLE)
+       return false;
+
    /* Determine the attnums we're looking for */
    foreach(lc, *varinfos)
    {

diff --git a/src/test/regress/expected/stats_ext.out b/src/test/regress/expected/stats_ext.out
index 66e770ab45a90b3c27557fe918716e395bd8b47a..620ffa2a5b507e5de9abfc3bd316a2ec54e32adf 100644 (file)
--- a/src/test/regress/expected/stats_ext.out
+++ b/src/test/regress/expected/stats_ext.out
@@ -172,6 +172,25 @@ SELECT * FROM check_estimated_rows('SELECT a, b FROM stxdinh* WHERE a = 0 AND b
 (1 row)
 
 DROP TABLE stxdinh, stxdinh1, stxdinh2;
+-- Ensure inherited stats ARE applied to inherited query in partitioned table
+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;
+VACUUM ANALYZE stxdinp; -- partitions are processed recursively
+SELECT 1 FROM pg_statistic_ext WHERE stxrelid = 'stxdinp'::regclass;
+ ?column? 
+----------
+        1
+(1 row)
+
+SELECT * FROM check_estimated_rows('SELECT a, b FROM stxdinp GROUP BY 1, 2');
+ estimated | actual 
+-----------+--------
+        10 |     10
+(1 row)
+
+DROP TABLE stxdinp;
 -- Verify supported object types for extended statistics
 CREATE schema tststats;
 CREATE TABLE tststats.t (a int, b int, c text);

diff --git a/src/test/regress/sql/stats_ext.sql b/src/test/regress/sql/stats_ext.sql
index 8ef6d56c3ee5258018c4cfae9c08c3045e3a208a..ffea1ac01efc0f433cf0d72ff1fd862f85ae7900 100644 (file)
--- a/src/test/regress/sql/stats_ext.sql
+++ b/src/test/regress/sql/stats_ext.sql
@@ -121,6 +121,16 @@ SELECT * FROM check_estimated_rows('SELECT a, b FROM stxdinh* GROUP BY 1, 2');
 SELECT * FROM check_estimated_rows('SELECT a, b FROM stxdinh* WHERE a = 0 AND b = 0');
 DROP TABLE stxdinh, stxdinh1, stxdinh2;
 
+-- Ensure inherited stats ARE applied to inherited query in partitioned table
+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;
+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');
+DROP TABLE stxdinp;
+
 -- Verify supported object types for extended statistics
 CREATE schema tststats;