Rework the pg_statistic_ext catalog

Since extended statistic got introduced in PostgreSQL 10, there was a
single catalog pg_statistic_ext storing both the definitions and built
statistic.  That's however problematic when a user is supposed to have
access only to the definitions, but not to user data.

Consider for example pg_dump on a database with RLS enabled - if the
pg_statistic_ext catalog respects RLS (which it should, if it contains
user data), pg_dump would not see any records and the result would not
define any extended statistics.  That would be a surprising behavior.

Until now this was not a pressing issue, because the existing types of
extended statistic (functional dependencies and ndistinct coefficients)
do not include any user data directly.  This changed with introduction
of MCV lists, which do include most common combinations of values.

The easiest way to fix this is to split the pg_statistic_ext catalog
into two - one for definitions, one for the built statistic values.
The new catalog is called pg_statistic_ext_data, and we're maintaining
a 1:1 relationship with the old catalog - either there are matching
records in both catalogs, or neither of them.

Bumped CATVERSION due to changing system catalog definitions.

Author: Dean Rasheed, with improvements by me
Reviewed-by: Dean Rasheed, John Naylor
Discussion: https://postgr.es/m/CAEZATCUhT9rt7Ui%3DVdx4N%3D%3DVV5XOK5dsXfnGgVOz_JhAicB%3DZA%40mail.gmail.com

21 files changed, 261 insertions, 94 deletions

diff --git a/src/backend/catalog/Makefile b/src/backend/catalog/Makefile
index f186198fc6c..8bece078dd1 100644
--- a/src/backend/catalog/Makefile
+++ b/src/backend/catalog/Makefile
@@ -34,7 +34,7 @@ CATALOG_HEADERS := \
 	pg_attrdef.h pg_constraint.h pg_inherits.h pg_index.h pg_operator.h \
 	pg_opfamily.h pg_opclass.h pg_am.h pg_amop.h pg_amproc.h \
 	pg_language.h pg_largeobject_metadata.h pg_largeobject.h pg_aggregate.h \
-	pg_statistic_ext.h \
+	pg_statistic_ext.h pg_statistic_ext_data.h \
 	pg_statistic.h pg_rewrite.h pg_trigger.h pg_event_trigger.h pg_description.h \
 	pg_cast.h pg_enum.h pg_namespace.h pg_conversion.h pg_depend.h \
 	pg_database.h pg_db_role_setting.h pg_tablespace.h pg_pltemplate.h \
diff --git a/src/backend/commands/statscmds.c b/src/backend/commands/statscmds.c
index 217d3a4533a..cf406f6f96b 100644
--- a/src/backend/commands/statscmds.c
+++ b/src/backend/commands/statscmds.c
@@ -23,6 +23,7 @@
 #include "catalog/namespace.h"
 #include "catalog/pg_namespace.h"
 #include "catalog/pg_statistic_ext.h"
+#include "catalog/pg_statistic_ext_data.h"
 #include "commands/comment.h"
 #include "commands/defrem.h"
 #include "miscadmin.h"
@@ -67,8 +68,11 @@ CreateStatistics(CreateStatsStmt *stmt)
 	HeapTuple	htup;
 	Datum		values[Natts_pg_statistic_ext];
 	bool		nulls[Natts_pg_statistic_ext];
+	Datum		datavalues[Natts_pg_statistic_ext_data];
+	bool		datanulls[Natts_pg_statistic_ext_data];
 	int2vector *stxkeys;
 	Relation	statrel;
+	Relation	datarel;
 	Relation	rel = NULL;
 	Oid			relid;
 	ObjectAddress parentobject,
@@ -336,11 +340,6 @@ CreateStatistics(CreateStatsStmt *stmt)
 	values[Anum_pg_statistic_ext_stxkeys - 1] = PointerGetDatum(stxkeys);
 	values[Anum_pg_statistic_ext_stxkind - 1] = PointerGetDatum(stxkind);
 
-	/* no statistics built yet */
-	nulls[Anum_pg_statistic_ext_stxndistinct - 1] = true;
-	nulls[Anum_pg_statistic_ext_stxdependencies - 1] = true;
-	nulls[Anum_pg_statistic_ext_stxmcv - 1] = true;
-
 	/* insert it into pg_statistic_ext */
 	htup = heap_form_tuple(statrel->rd_att, values, nulls);
 	CatalogTupleInsert(statrel, htup);
@@ -349,6 +348,29 @@ CreateStatistics(CreateStatsStmt *stmt)
 	relation_close(statrel, RowExclusiveLock);
 
 	/*
+	 * Also build the pg_statistic_ext_data tuple, to hold the actual
+	 * statistics data.
+	 */
+	datarel = table_open(StatisticExtDataRelationId, RowExclusiveLock);
+
+	memset(datavalues, 0, sizeof(datavalues));
+	memset(datanulls, false, sizeof(datanulls));
+
+	datavalues[Anum_pg_statistic_ext_data_stxoid - 1] = ObjectIdGetDatum(statoid);
+
+	/* no statistics built yet */
+	datanulls[Anum_pg_statistic_ext_data_stxdndistinct - 1] = true;
+	datanulls[Anum_pg_statistic_ext_data_stxddependencies - 1] = true;
+	datanulls[Anum_pg_statistic_ext_data_stxdmcv - 1] = true;
+
+	/* insert it into pg_statistic_ext_data */
+	htup = heap_form_tuple(datarel->rd_att, datavalues, datanulls);
+	CatalogTupleInsert(datarel, htup);
+	heap_freetuple(htup);
+
+	relation_close(datarel, RowExclusiveLock);
+
+	/*
 	 * Invalidate relcache so that others see the new statistics object.
 	 */
 	CacheInvalidateRelcache(rel);
@@ -404,6 +426,23 @@ RemoveStatisticsById(Oid statsOid)
 	Oid			relid;
 
 	/*
+	 * First delete the pg_statistic_ext_data tuple holding the actual
+	 * statistical data.
+	 */
+	relation = table_open(StatisticExtDataRelationId, RowExclusiveLock);
+
+	tup = SearchSysCache1(STATEXTDATASTXOID, ObjectIdGetDatum(statsOid));
+
+	if (!HeapTupleIsValid(tup)) /* should not happen */
+		elog(ERROR, "cache lookup failed for statistics data %u", statsOid);
+
+	CatalogTupleDelete(relation, &tup->t_self);
+
+	ReleaseSysCache(tup);
+
+	table_close(relation, RowExclusiveLock);
+
+	/*
 	 * Delete the pg_statistic_ext tuple.  Also send out a cache inval on the
 	 * associated table, so that dependent plans will be rebuilt.
 	 */
@@ -431,8 +470,8 @@ RemoveStatisticsById(Oid statsOid)
  *
  * This could throw an error if the type change can't be supported.
  * If it can be supported, but the stats must be recomputed, a likely choice
- * would be to set the relevant column(s) of the pg_statistic_ext tuple to
- * null until the next ANALYZE.  (Note that the type change hasn't actually
+ * would be to set the relevant column(s) of the pg_statistic_ext_data tuple
+ * to null until the next ANALYZE.  (Note that the type change hasn't actually
  * happened yet, so one option that's *not* on the table is to recompute
  * immediately.)
  *
@@ -456,11 +495,11 @@ UpdateStatisticsForTypeChange(Oid statsOid, Oid relationOid, int attnum,
 
 	Relation	rel;
 
-	Datum		values[Natts_pg_statistic_ext];
-	bool		nulls[Natts_pg_statistic_ext];
-	bool		replaces[Natts_pg_statistic_ext];
+	Datum		values[Natts_pg_statistic_ext_data];
+	bool		nulls[Natts_pg_statistic_ext_data];
+	bool		replaces[Natts_pg_statistic_ext_data];
 
-	oldtup = SearchSysCache1(STATEXTOID, ObjectIdGetDatum(statsOid));
+	oldtup = SearchSysCache1(STATEXTDATASTXOID, ObjectIdGetDatum(statsOid));
 	if (!HeapTupleIsValid(oldtup))
 		elog(ERROR, "cache lookup failed for statistics object %u", statsOid);
 
@@ -479,14 +518,14 @@ UpdateStatisticsForTypeChange(Oid statsOid, Oid relationOid, int attnum,
 	 * OK, we need to reset some statistics. So let's build the new tuple,
 	 * replacing the affected statistics types with NULL.
 	 */
-	memset(nulls, 0, Natts_pg_statistic_ext * sizeof(bool));
-	memset(replaces, 0, Natts_pg_statistic_ext * sizeof(bool));
-	memset(values, 0, Natts_pg_statistic_ext * sizeof(Datum));
+	memset(nulls, 0, Natts_pg_statistic_ext_data * sizeof(bool));
+	memset(replaces, 0, Natts_pg_statistic_ext_data * sizeof(bool));
+	memset(values, 0, Natts_pg_statistic_ext_data * sizeof(Datum));
 
-	replaces[Anum_pg_statistic_ext_stxmcv - 1] = true;
-	nulls[Anum_pg_statistic_ext_stxmcv - 1] = true;
+	replaces[Anum_pg_statistic_ext_data_stxdmcv - 1] = true;
+	nulls[Anum_pg_statistic_ext_data_stxdmcv - 1] = true;
 
-	rel = heap_open(StatisticExtRelationId, RowExclusiveLock);
+	rel = heap_open(StatisticExtDataRelationId, RowExclusiveLock);
 
 	/* replace the old tuple */
 	stup = heap_modify_tuple(oldtup,
diff --git a/src/backend/optimizer/util/plancat.c b/src/backend/optimizer/util/plancat.c
index 2405acbf6fa..40f497660d1 100644
--- a/src/backend/optimizer/util/plancat.c
+++ b/src/backend/optimizer/util/plancat.c
@@ -1308,6 +1308,7 @@ get_relation_statistics(RelOptInfo *rel, Relation relation)
 		Oid			statOid = lfirst_oid(l);
 		Form_pg_statistic_ext staForm;
 		HeapTuple	htup;
+		HeapTuple	dtup;
 		Bitmapset  *keys = NULL;
 		int			i;
 
@@ -1316,6 +1317,10 @@ get_relation_statistics(RelOptInfo *rel, Relation relation)
 			elog(ERROR, "cache lookup failed for statistics object %u", statOid);
 		staForm = (Form_pg_statistic_ext) GETSTRUCT(htup);
 
+		dtup = SearchSysCache1(STATEXTDATASTXOID, ObjectIdGetDatum(statOid));
+		if (!HeapTupleIsValid(dtup))
+			elog(ERROR, "cache lookup failed for statistics object %u", statOid);
+
 		/*
 		 * First, build the array of columns covered.  This is ultimately
 		 * wasted if no stats within the object have actually been built, but
@@ -1325,7 +1330,7 @@ get_relation_statistics(RelOptInfo *rel, Relation relation)
 			keys = bms_add_member(keys, staForm->stxkeys.values[i]);
 
 		/* add one StatisticExtInfo for each kind built */
-		if (statext_is_kind_built(htup, STATS_EXT_NDISTINCT))
+		if (statext_is_kind_built(dtup, STATS_EXT_NDISTINCT))
 		{
 			StatisticExtInfo *info = makeNode(StatisticExtInfo);
 
@@ -1337,7 +1342,7 @@ get_relation_statistics(RelOptInfo *rel, Relation relation)
 			stainfos = lcons(info, stainfos);
 		}
 
-		if (statext_is_kind_built(htup, STATS_EXT_DEPENDENCIES))
+		if (statext_is_kind_built(dtup, STATS_EXT_DEPENDENCIES))
 		{
 			StatisticExtInfo *info = makeNode(StatisticExtInfo);
 
@@ -1349,7 +1354,7 @@ get_relation_statistics(RelOptInfo *rel, Relation relation)
 			stainfos = lcons(info, stainfos);
 		}
 
-		if (statext_is_kind_built(htup, STATS_EXT_MCV))
+		if (statext_is_kind_built(dtup, STATS_EXT_MCV))
 		{
 			StatisticExtInfo *info = makeNode(StatisticExtInfo);
 
@@ -1362,6 +1367,7 @@ get_relation_statistics(RelOptInfo *rel, Relation relation)
 		}
 
 		ReleaseSysCache(htup);
+		ReleaseSysCache(dtup);
 		bms_free(keys);
 	}
 
diff --git a/src/backend/statistics/README.mcv b/src/backend/statistics/README.mcv
index c18878f5d2b..8455b0d13f6 100644
--- a/src/backend/statistics/README.mcv
+++ b/src/backend/statistics/README.mcv
@@ -86,11 +86,14 @@ So instead the MCV lists are stored in a custom data type (pg_mcv_list),
 which however makes it more difficult to inspect the contents. To make that
 easier, there's a SRF returning detailed information about the MCV lists.
 
-    SELECT m.* FROM pg_statistic_ext,
-                    pg_mcv_list_items(stxmcv) m WHERE stxname = 'stts2';
+    SELECT m.* FROM pg_statistic_ext s,
+                    pg_statistic_ext_data d,
+                    pg_mcv_list_items(stxdmcv) m
+              WHERE s.stxname = 'stts2'
+                AND d.stxoid = s.oid;
 
 It accepts one parameter - a pg_mcv_list value (which can only be obtained
-from pg_statistic_ext catalog, to defend against malicious input), and
+from pg_statistic_ext_data catalog, to defend against malicious input), and
 returns these columns:
 
     - item index (0, ..., (nitems-1))
diff --git a/src/backend/statistics/dependencies.c b/src/backend/statistics/dependencies.c
index cd318faf3b9..66c38ce2bc9 100644
--- a/src/backend/statistics/dependencies.c
+++ b/src/backend/statistics/dependencies.c
@@ -17,6 +17,7 @@
 #include "access/sysattr.h"
 #include "catalog/pg_operator.h"
 #include "catalog/pg_statistic_ext.h"
+#include "catalog/pg_statistic_ext_data.h"
 #include "lib/stringinfo.h"
 #include "nodes/nodeFuncs.h"
 #include "optimizer/clauses.h"
@@ -637,12 +638,12 @@ statext_dependencies_load(Oid mvoid)
 	Datum		deps;
 	HeapTuple	htup;
 
-	htup = SearchSysCache1(STATEXTOID, ObjectIdGetDatum(mvoid));
+	htup = SearchSysCache1(STATEXTDATASTXOID, ObjectIdGetDatum(mvoid));
 	if (!HeapTupleIsValid(htup))
 		elog(ERROR, "cache lookup failed for statistics object %u", mvoid);
 
-	deps = SysCacheGetAttr(STATEXTOID, htup,
-						   Anum_pg_statistic_ext_stxdependencies, &isnull);
+	deps = SysCacheGetAttr(STATEXTDATASTXOID, htup,
+						   Anum_pg_statistic_ext_data_stxddependencies, &isnull);
 	if (isnull)
 		elog(ERROR,
 			 "requested statistic kind \"%c\" is not yet built for statistics object %u",
diff --git a/src/backend/statistics/extended_stats.c b/src/backend/statistics/extended_stats.c
index ab187915c1d..96db32f0a0a 100644
--- a/src/backend/statistics/extended_stats.c
+++ b/src/backend/statistics/extended_stats.c
@@ -23,6 +23,7 @@
 #include "catalog/indexing.h"
 #include "catalog/pg_collation.h"
 #include "catalog/pg_statistic_ext.h"
+#include "catalog/pg_statistic_ext_data.h"
 #include "nodes/nodeFuncs.h"
 #include "optimizer/clauses.h"
 #include "optimizer/optimizer.h"
@@ -65,9 +66,9 @@ typedef struct StatExtEntry
 static List *fetch_statentries_for_relation(Relation pg_statext, Oid relid);
 static VacAttrStats **lookup_var_attr_stats(Relation rel, Bitmapset *attrs,
 											int nvacatts, VacAttrStats **vacatts);
-static void statext_store(Relation pg_stext, Oid relid,
+static void statext_store(Oid relid,
 						  MVNDistinct *ndistinct, MVDependencies *dependencies,
-						  MCVList *mcvlist, VacAttrStats **stats);
+						  MCVList *mcv, VacAttrStats **stats);
 
 
 /*
@@ -145,7 +146,7 @@ BuildRelationExtStatistics(Relation onerel, double totalrows,
 		}
 
 		/* store the statistics in the catalog */
-		statext_store(pg_stext, stat->statOid, ndistinct, dependencies, mcv, stats);
+		statext_store(stat->statOid, ndistinct, dependencies, mcv, stats);
 	}
 
 	table_close(pg_stext, RowExclusiveLock);
@@ -156,7 +157,7 @@ BuildRelationExtStatistics(Relation onerel, double totalrows,
 
 /*
  * statext_is_kind_built
- *		Is this stat kind built in the given pg_statistic_ext tuple?
+ *		Is this stat kind built in the given pg_statistic_ext_data tuple?
  */
 bool
 statext_is_kind_built(HeapTuple htup, char type)
@@ -166,15 +167,15 @@ statext_is_kind_built(HeapTuple htup, char type)
 	switch (type)
 	{
 		case STATS_EXT_NDISTINCT:
-			attnum = Anum_pg_statistic_ext_stxndistinct;
+			attnum = Anum_pg_statistic_ext_data_stxdndistinct;
 			break;
 
 		case STATS_EXT_DEPENDENCIES:
-			attnum = Anum_pg_statistic_ext_stxdependencies;
+			attnum = Anum_pg_statistic_ext_data_stxddependencies;
 			break;
 
 		case STATS_EXT_MCV:
-			attnum = Anum_pg_statistic_ext_stxmcv;
+			attnum = Anum_pg_statistic_ext_data_stxdmcv;
 			break;
 
 		default:
@@ -312,70 +313,76 @@ lookup_var_attr_stats(Relation rel, Bitmapset *attrs,
 
 /*
  * statext_store
- *	Serializes the statistics and stores them into the pg_statistic_ext tuple.
+ *	Serializes the statistics and stores them into the pg_statistic_ext_data
+ *	tuple.
  */
 static void
-statext_store(Relation pg_stext, Oid statOid,
+statext_store(Oid statOid,
 			  MVNDistinct *ndistinct, MVDependencies *dependencies,
 			  MCVList *mcv, VacAttrStats **stats)
 {
 	HeapTuple	stup,
 				oldtup;
-	Datum		values[Natts_pg_statistic_ext];
-	bool		nulls[Natts_pg_statistic_ext];
-	bool		replaces[Natts_pg_statistic_ext];
+	Datum		values[Natts_pg_statistic_ext_data];
+	bool		nulls[Natts_pg_statistic_ext_data];
+	bool		replaces[Natts_pg_statistic_ext_data];
+	Relation	pg_stextdata;
 
 	memset(nulls, true, sizeof(nulls));
 	memset(replaces, false, sizeof(replaces));
 	memset(values, 0, sizeof(values));
 
 	/*
-	 * Construct a new pg_statistic_ext tuple, replacing the calculated stats.
+	 * Construct a new pg_statistic_ext_data tuple, replacing the calculated
+	 * stats.
 	 */
 	if (ndistinct != NULL)
 	{
 		bytea	   *data = statext_ndistinct_serialize(ndistinct);
 
-		nulls[Anum_pg_statistic_ext_stxndistinct - 1] = (data == NULL);
-		values[Anum_pg_statistic_ext_stxndistinct - 1] = PointerGetDatum(data);
+		nulls[Anum_pg_statistic_ext_data_stxdndistinct - 1] = (data == NULL);
+		values[Anum_pg_statistic_ext_data_stxdndistinct - 1] = PointerGetDatum(data);
 	}
 
 	if (dependencies != NULL)
 	{
 		bytea	   *data = statext_dependencies_serialize(dependencies);
 
-		nulls[Anum_pg_statistic_ext_stxdependencies - 1] = (data == NULL);
-		values[Anum_pg_statistic_ext_stxdependencies - 1] = PointerGetDatum(data);
+		nulls[Anum_pg_statistic_ext_data_stxddependencies - 1] = (data == NULL);
+		values[Anum_pg_statistic_ext_data_stxddependencies - 1] = PointerGetDatum(data);
 	}
-
 	if (mcv != NULL)
 	{
 		bytea	   *data = statext_mcv_serialize(mcv, stats);
 
-		nulls[Anum_pg_statistic_ext_stxmcv - 1] = (data == NULL);
-		values[Anum_pg_statistic_ext_stxmcv - 1] = PointerGetDatum(data);
+		nulls[Anum_pg_statistic_ext_data_stxdmcv - 1] = (data == NULL);
+		values[Anum_pg_statistic_ext_data_stxdmcv - 1] = PointerGetDatum(data);
 	}
 
 	/* always replace the value (either by bytea or NULL) */
-	replaces[Anum_pg_statistic_ext_stxndistinct - 1] = true;
-	replaces[Anum_pg_statistic_ext_stxdependencies - 1] = true;
-	replaces[Anum_pg_statistic_ext_stxmcv - 1] = true;
+	replaces[Anum_pg_statistic_ext_data_stxdndistinct - 1] = true;
+	replaces[Anum_pg_statistic_ext_data_stxddependencies - 1] = true;
+	replaces[Anum_pg_statistic_ext_data_stxdmcv - 1] = true;
 
-	/* there should already be a pg_statistic_ext tuple */
-	oldtup = SearchSysCache1(STATEXTOID, ObjectIdGetDatum(statOid));
+	/* there should already be a pg_statistic_ext_data tuple */
+	oldtup = SearchSysCache1(STATEXTDATASTXOID, ObjectIdGetDatum(statOid));
 	if (!HeapTupleIsValid(oldtup))
 		elog(ERROR, "cache lookup failed for statistics object %u", statOid);
 
 	/* replace it */
+	pg_stextdata = table_open(StatisticExtDataRelationId, RowExclusiveLock);
+
 	stup = heap_modify_tuple(oldtup,
-							 RelationGetDescr(pg_stext),
+							 RelationGetDescr(pg_stextdata),
 							 values,
 							 nulls,
 							 replaces);
 	ReleaseSysCache(oldtup);
-	CatalogTupleUpdate(pg_stext, &stup->t_self, stup);
+	CatalogTupleUpdate(pg_stextdata, &stup->t_self, stup);
 
 	heap_freetuple(stup);
+
+	table_close(pg_stextdata, RowExclusiveLock);
 }
 
 /* initialize multi-dimensional sort */
diff --git a/src/backend/statistics/mcv.c b/src/backend/statistics/mcv.c
index d1f0fd55e83..2feb17ed447 100644
--- a/src/backend/statistics/mcv.c
+++ b/src/backend/statistics/mcv.c
@@ -19,6 +19,7 @@
 #include "access/htup_details.h"
 #include "catalog/pg_collation.h"
 #include "catalog/pg_statistic_ext.h"
+#include "catalog/pg_statistic_ext_data.h"
 #include "fmgr.h"
 #include "funcapi.h"
 #include "nodes/nodeFuncs.h"
@@ -429,13 +430,13 @@ statext_mcv_load(Oid mvoid)
 	MCVList    *result;
 	bool		isnull;
 	Datum		mcvlist;
-	HeapTuple	htup = SearchSysCache1(STATEXTOID, ObjectIdGetDatum(mvoid));
+	HeapTuple	htup = SearchSysCache1(STATEXTDATASTXOID, ObjectIdGetDatum(mvoid));
 
 	if (!HeapTupleIsValid(htup))
 		elog(ERROR, "cache lookup failed for statistics object %u", mvoid);
 
-	mcvlist = SysCacheGetAttr(STATEXTOID, htup,
-							  Anum_pg_statistic_ext_stxmcv, &isnull);
+	mcvlist = SysCacheGetAttr(STATEXTDATASTXOID, htup,
+							  Anum_pg_statistic_ext_data_stxdmcv, &isnull);
 
 	if (isnull)
 		elog(ERROR,
diff --git a/src/backend/statistics/mvdistinct.c b/src/backend/statistics/mvdistinct.c
index 7432a6a3969..9ebf183d909 100644
--- a/src/backend/statistics/mvdistinct.c
+++ b/src/backend/statistics/mvdistinct.c
@@ -27,6 +27,7 @@
 
 #include "access/htup_details.h"
 #include "catalog/pg_statistic_ext.h"
+#include "catalog/pg_statistic_ext_data.h"
 #include "utils/fmgrprotos.h"
 #include "utils/lsyscache.h"
 #include "lib/stringinfo.h"
@@ -145,12 +146,12 @@ statext_ndistinct_load(Oid mvoid)
 	Datum		ndist;
 	HeapTuple	htup;
 
-	htup = SearchSysCache1(STATEXTOID, ObjectIdGetDatum(mvoid));
+	htup = SearchSysCache1(STATEXTDATASTXOID, ObjectIdGetDatum(mvoid));
 	if (!HeapTupleIsValid(htup))
 		elog(ERROR, "cache lookup failed for statistics object %u", mvoid);
 
-	ndist = SysCacheGetAttr(STATEXTOID, htup,
-							Anum_pg_statistic_ext_stxndistinct, &isnull);
+	ndist = SysCacheGetAttr(STATEXTDATASTXOID, htup,
+							Anum_pg_statistic_ext_data_stxdndistinct, &isnull);
 	if (isnull)
 		elog(ERROR,
 			 "requested statistic kind \"%c\" is not yet built for statistics object %u",
diff --git a/src/backend/utils/cache/syscache.c b/src/backend/utils/cache/syscache.c
index 476538354dd..99976468e5c 100644
--- a/src/backend/utils/cache/syscache.c
+++ b/src/backend/utils/cache/syscache.c
@@ -62,6 +62,7 @@
 #include "catalog/pg_replication_origin.h"
 #include "catalog/pg_statistic.h"
 #include "catalog/pg_statistic_ext.h"
+#include "catalog/pg_statistic_ext_data.h"
 #include "catalog/pg_subscription.h"
 #include "catalog/pg_subscription_rel.h"
 #include "catalog/pg_tablespace.h"
@@ -727,6 +728,17 @@ static const struct cachedesc cacheinfo[] = {
 		},
 		32
 	},
+	{StatisticExtDataRelationId, /* STATEXTDATASTXOID */
+		StatisticExtDataStxoidIndexId,
+		1,
+		{
+			Anum_pg_statistic_ext_data_stxoid,
+			0,
+			0,
+			0
+		},
+		4
+	},
 	{StatisticExtRelationId,	/* STATEXTNAMENSP */
 		StatisticExtNameIndexId,
 		2,
diff --git a/src/include/catalog/catversion.h b/src/include/catalog/catversion.h
index 4b8ee1cbdb4..e034506751d 100644
--- a/src/include/catalog/catversion.h
+++ b/src/include/catalog/catversion.h
@@ -53,6 +53,6 @@
  */
 
 /*							yyyymmddN */
-#define CATALOG_VERSION_NO	201906041
+#define CATALOG_VERSION_NO	201906151
 
 #endif
diff --git a/src/include/catalog/indexing.h b/src/include/catalog/indexing.h
index 5f2aee8a4a9..ef4445b017a 100644
--- a/src/include/catalog/indexing.h
+++ b/src/include/catalog/indexing.h
@@ -186,13 +186,6 @@ DECLARE_UNIQUE_INDEX(pg_largeobject_loid_pn_index, 2683, on pg_largeobject using
 DECLARE_UNIQUE_INDEX(pg_largeobject_metadata_oid_index, 2996, on pg_largeobject_metadata using btree(oid oid_ops));
 #define LargeObjectMetadataOidIndexId	2996
 
-DECLARE_UNIQUE_INDEX(pg_statistic_ext_oid_index, 3380, on pg_statistic_ext using btree(oid oid_ops));
-#define StatisticExtOidIndexId	3380
-DECLARE_UNIQUE_INDEX(pg_statistic_ext_name_index, 3997, on pg_statistic_ext using btree(stxname name_ops, stxnamespace oid_ops));
-#define StatisticExtNameIndexId 3997
-DECLARE_INDEX(pg_statistic_ext_relid_index, 3379, on pg_statistic_ext using btree(stxrelid oid_ops));
-#define StatisticExtRelidIndexId 3379
-
 DECLARE_UNIQUE_INDEX(pg_namespace_nspname_index, 2684, on pg_namespace using btree(nspname name_ops));
 #define NamespaceNameIndexId  2684
 DECLARE_UNIQUE_INDEX(pg_namespace_oid_index, 2685, on pg_namespace using btree(oid oid_ops));
@@ -237,6 +230,16 @@ DECLARE_INDEX(pg_shdepend_reference_index, 1233, on pg_shdepend using btree(refc
 DECLARE_UNIQUE_INDEX(pg_statistic_relid_att_inh_index, 2696, on pg_statistic using btree(starelid oid_ops, staattnum int2_ops, stainherit bool_ops));
 #define StatisticRelidAttnumInhIndexId	2696
 
+DECLARE_UNIQUE_INDEX(pg_statistic_ext_oid_index, 3380, on pg_statistic_ext using btree(oid oid_ops));
+#define StatisticExtOidIndexId	3380
+DECLARE_UNIQUE_INDEX(pg_statistic_ext_name_index, 3997, on pg_statistic_ext using btree(stxname name_ops, stxnamespace oid_ops));
+#define StatisticExtNameIndexId 3997
+DECLARE_INDEX(pg_statistic_ext_relid_index, 3379, on pg_statistic_ext using btree(stxrelid oid_ops));
+#define StatisticExtRelidIndexId 3379
+
+DECLARE_UNIQUE_INDEX(pg_statistic_ext_data_stxoid_index, 3433, on pg_statistic_ext_data using btree(stxoid oid_ops));
+#define StatisticExtDataStxoidIndexId 3433
+
 DECLARE_UNIQUE_INDEX(pg_tablespace_oid_index, 2697, on pg_tablespace using btree(oid oid_ops));
 #define TablespaceOidIndexId  2697
 DECLARE_UNIQUE_INDEX(pg_tablespace_spcname_index, 2698, on pg_tablespace using btree(spcname name_ops));
diff --git a/src/include/catalog/pg_statistic_ext.h b/src/include/catalog/pg_statistic_ext.h
index e449f9efe8b..d8c5e0651ec 100644
--- a/src/include/catalog/pg_statistic_ext.h
+++ b/src/include/catalog/pg_statistic_ext.h
@@ -1,8 +1,12 @@
 /*-------------------------------------------------------------------------
  *
  * pg_statistic_ext.h
- *	  definition of the "extended statistics" system catalog (pg_statistic_ext)
+ *	  definition of the "extended statistics" system catalog
+ *	  (pg_statistic_ext)
  *
+ * Note that pg_statistic_ext contains the definitions of extended statistics
+ * objects, created by CREATE STATISTICS, but not the actual statistical data,
+ * created by running ANALYZE.
  *
  * Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
@@ -47,9 +51,6 @@ CATALOG(pg_statistic_ext,3381,StatisticExtRelationId)
 #ifdef CATALOG_VARLEN
 	char		stxkind[1] BKI_FORCE_NOT_NULL;	/* statistics kinds requested
 												 * to build */
-	pg_ndistinct stxndistinct;	/* ndistinct coefficients (serialized) */
-	pg_dependencies stxdependencies;	/* dependencies (serialized) */
-	pg_mcv_list stxmcv;			/* MCV (serialized) */
 #endif
 
 } FormData_pg_statistic_ext;
diff --git a/src/include/catalog/pg_statistic_ext_data.h b/src/include/catalog/pg_statistic_ext_data.h
new file mode 100644
index 00000000000..5da9bc8ae2c
--- /dev/null
+++ b/src/include/catalog/pg_statistic_ext_data.h
@@ -0,0 +1,52 @@
+/*-------------------------------------------------------------------------
+ *
+ * pg_statistic_ext_data.h
+ *	  definition of the "extended statistics data" system catalog
+ *	  (pg_statistic_ext_data)
+ *
+ * This catalog stores the statistical data for extended statistics objects.
+ *
+ * Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * src/include/catalog/pg_statistic_ext_data.h
+ *
+ * NOTES
+ *	  The Catalog.pm module reads this file and derives schema
+ *	  information.
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef PG_STATISTIC_EXT_DATA_H
+#define PG_STATISTIC_EXT_DATA_H
+
+#include "catalog/genbki.h"
+#include "catalog/pg_statistic_ext_data_d.h"
+
+/* ----------------
+ *		pg_statistic_ext_data definition.  cpp turns this into
+ *		typedef struct FormData_pg_statistic_ext_data
+ * ----------------
+ */
+CATALOG(pg_statistic_ext_data,3429,StatisticExtDataRelationId)
+{
+	Oid			stxoid;			/* statistics object this data is for */
+
+#ifdef CATALOG_VARLEN			/* variable-length fields start here */
+
+	pg_ndistinct stxdndistinct;	/* ndistinct coefficients (serialized) */
+	pg_dependencies stxddependencies;	/* dependencies (serialized) */
+	pg_mcv_list stxdmcv;			/* MCV (serialized) */
+
+#endif
+
+} FormData_pg_statistic_ext_data;
+
+/* ----------------
+ *		Form_pg_statistic_ext_data corresponds to a pointer to a tuple with
+ *		the format of pg_statistic_ext_data relation.
+ * ----------------
+ */
+typedef FormData_pg_statistic_ext_data *Form_pg_statistic_ext_data;
+
+#endif							/* PG_STATISTIC_EXT_DATA_H */
diff --git a/src/include/catalog/toasting.h b/src/include/catalog/toasting.h
index a9e633d6bb5..cc5dfed0bf6 100644
--- a/src/include/catalog/toasting.h
+++ b/src/include/catalog/toasting.h
@@ -70,6 +70,7 @@ DECLARE_TOAST(pg_rewrite, 2838, 2839);
 DECLARE_TOAST(pg_seclabel, 3598, 3599);
 DECLARE_TOAST(pg_statistic, 2840, 2841);
 DECLARE_TOAST(pg_statistic_ext, 3439, 3440);
+DECLARE_TOAST(pg_statistic_ext_data, 3430, 3431);
 DECLARE_TOAST(pg_trigger, 2336, 2337);
 DECLARE_TOAST(pg_ts_dict, 4169, 4170);
 DECLARE_TOAST(pg_type, 4171, 4172);
diff --git a/src/include/utils/syscache.h b/src/include/utils/syscache.h
index a6307474eed..918765cc993 100644
--- a/src/include/utils/syscache.h
+++ b/src/include/utils/syscache.h
@@ -86,6 +86,7 @@ enum SysCacheIdentifier
 	REPLORIGNAME,
 	RULERELNAME,
 	SEQRELID,
+	STATEXTDATASTXOID,
 	STATEXTNAMENSP,
 	STATEXTOID,
 	STATRELATTINH,
diff --git a/src/test/regress/expected/oidjoins.out b/src/test/regress/expected/oidjoins.out
index 4edc8175aa2..1302cc271ba 100644
--- a/src/test/regress/expected/oidjoins.out
+++ b/src/test/regress/expected/oidjoins.out
@@ -985,6 +985,14 @@ WHERE	stxowner != 0 AND
 ------+----------
 (0 rows)
 
+SELECT	ctid, stxoid
+FROM	pg_catalog.pg_statistic_ext_data fk
+WHERE	stxoid != 0 AND
+	NOT EXISTS(SELECT 1 FROM pg_catalog.pg_statistic_ext pk WHERE pk.oid = fk.stxoid);
+ ctid | stxoid 
+------+--------
+(0 rows)
+
 SELECT	ctid, spcowner
 FROM	pg_catalog.pg_tablespace fk
 WHERE	spcowner != 0 AND
diff --git a/src/test/regress/expected/sanity_check.out b/src/test/regress/expected/sanity_check.out
index 392e8a49574..8ff0da185e3 100644
--- a/src/test/regress/expected/sanity_check.out
+++ b/src/test/regress/expected/sanity_check.out
@@ -149,6 +149,7 @@ pg_shdescription|t
 pg_shseclabel|t
 pg_statistic|t
 pg_statistic_ext|t
+pg_statistic_ext_data|t
 pg_subscription|t
 pg_subscription_rel|t
 pg_tablespace|t
diff --git a/src/test/regress/expected/stats_ext.out b/src/test/regress/expected/stats_ext.out
index 046d0b17217..def95d80c9b 100644
--- a/src/test/regress/expected/stats_ext.out
+++ b/src/test/regress/expected/stats_ext.out
@@ -199,9 +199,11 @@ SELECT * FROM check_estimated_rows('SELECT COUNT(*) FROM ndistinct GROUP BY b, c
 -- correct command
 CREATE STATISTICS s10 ON a, b, c FROM ndistinct;
 ANALYZE ndistinct;
-SELECT stxkind, stxndistinct
-  FROM pg_statistic_ext WHERE stxrelid = 'ndistinct'::regclass;
- stxkind |                    stxndistinct                     
+SELECT s.stxkind, d.stxdndistinct
+  FROM pg_statistic_ext s, pg_statistic_ext_data d
+ WHERE s.stxrelid = 'ndistinct'::regclass
+   AND d.stxoid = s.oid;
+ stxkind |                    stxdndistinct                    
 ---------+-----------------------------------------------------
  {d,f,m} | {"3, 4": 11, "3, 6": 11, "4, 6": 11, "3, 4, 6": 11}
 (1 row)
@@ -246,9 +248,11 @@ INSERT INTO ndistinct (a, b, c, filler1)
             cash_words(mod(i,33)::int::money)
        FROM generate_series(1,5000) s(i);
 ANALYZE ndistinct;
-SELECT stxkind, stxndistinct
-  FROM pg_statistic_ext WHERE stxrelid = 'ndistinct'::regclass;
- stxkind |                        stxndistinct                        
+SELECT s.stxkind, d.stxdndistinct
+  FROM pg_statistic_ext s, pg_statistic_ext_data d
+ WHERE s.stxrelid = 'ndistinct'::regclass
+   AND d.stxoid = s.oid;
+ stxkind |                       stxdndistinct                        
 ---------+------------------------------------------------------------
  {d,f,m} | {"3, 4": 2550, "3, 6": 800, "4, 6": 1632, "3, 4, 6": 5000}
 (1 row)
@@ -285,10 +289,12 @@ SELECT * FROM check_estimated_rows('SELECT COUNT(*) FROM ndistinct GROUP BY a, d
 (1 row)
 
 DROP STATISTICS s10;
-SELECT stxkind, stxndistinct
-  FROM pg_statistic_ext WHERE stxrelid = 'ndistinct'::regclass;
- stxkind | stxndistinct 
----------+--------------
+SELECT s.stxkind, d.stxdndistinct
+  FROM pg_statistic_ext s, pg_statistic_ext_data d
+ WHERE s.stxrelid = 'ndistinct'::regclass
+   AND d.stxoid = s.oid;
+ stxkind | stxdndistinct 
+---------+---------------
 (0 rows)
 
 -- dropping the statistics results in under-estimates
@@ -537,7 +543,10 @@ SELECT * FROM check_estimated_rows('SELECT * FROM mcv_lists WHERE a <= 4 AND b <
 
 -- check change of unrelated column type does not reset the MCV statistics
 ALTER TABLE mcv_lists ALTER COLUMN d TYPE VARCHAR(64);
-SELECT stxmcv IS NOT NULL FROM pg_statistic_ext WHERE stxname = 'mcv_lists_stats';
+SELECT d.stxdmcv IS NOT NULL
+  FROM pg_statistic_ext s, pg_statistic_ext_data d
+ WHERE s.stxname = 'mcv_lists_stats'
+   AND d.stxoid = s.oid;
  ?column? 
 ----------
  t
@@ -600,8 +609,11 @@ SELECT * FROM check_estimated_rows('SELECT * FROM mcv_lists WHERE a IS NULL AND
 TRUNCATE mcv_lists;
 INSERT INTO mcv_lists (a, b, c) SELECT 1, 2, 3 FROM generate_series(1,1000) s(i);
 ANALYZE mcv_lists;
-SELECT m.* FROM pg_statistic_ext,
-              pg_mcv_list_items(stxmcv) m WHERE stxname = 'mcv_lists_stats';
+SELECT m.*
+  FROM pg_statistic_ext s, pg_statistic_ext_data d,
+       pg_mcv_list_items(d.stxdmcv) m
+ WHERE s.stxname = 'mcv_lists_stats'
+   AND d.stxoid = s.oid;
  index |  values   |  nulls  | frequency | base_frequency 
 -------+-----------+---------+-----------+----------------
      0 | {1, 2, 3} | {f,f,f} |         1 |              1
diff --git a/src/test/regress/sql/oidjoins.sql b/src/test/regress/sql/oidjoins.sql
index dbe4a5857d9..b774cbca5b6 100644
--- a/src/test/regress/sql/oidjoins.sql
+++ b/src/test/regress/sql/oidjoins.sql
@@ -493,6 +493,10 @@ SELECT	ctid, stxowner
 FROM	pg_catalog.pg_statistic_ext fk
 WHERE	stxowner != 0 AND
 	NOT EXISTS(SELECT 1 FROM pg_catalog.pg_authid pk WHERE pk.oid = fk.stxowner);
+SELECT	ctid, stxoid
+FROM	pg_catalog.pg_statistic_ext_data fk
+WHERE	stxoid != 0 AND
+	NOT EXISTS(SELECT 1 FROM pg_catalog.pg_statistic_ext pk WHERE pk.oid = fk.stxoid);
 SELECT	ctid, spcowner
 FROM	pg_catalog.pg_tablespace fk
 WHERE	spcowner != 0 AND
diff --git a/src/test/regress/sql/stats_ext.sql b/src/test/regress/sql/stats_ext.sql
index d3337308724..3aa99d7bc81 100644
--- a/src/test/regress/sql/stats_ext.sql
+++ b/src/test/regress/sql/stats_ext.sql
@@ -144,8 +144,10 @@ CREATE STATISTICS s10 ON a, b, c FROM ndistinct;
 
 ANALYZE ndistinct;
 
-SELECT stxkind, stxndistinct
-  FROM pg_statistic_ext WHERE stxrelid = 'ndistinct'::regclass;
+SELECT s.stxkind, d.stxdndistinct
+  FROM pg_statistic_ext s, pg_statistic_ext_data d
+ WHERE s.stxrelid = 'ndistinct'::regclass
+   AND d.stxoid = s.oid;
 
 -- Hash Aggregate, thanks to estimates improved by the statistic
 SELECT * FROM check_estimated_rows('SELECT COUNT(*) FROM ndistinct GROUP BY a, b');
@@ -170,8 +172,10 @@ INSERT INTO ndistinct (a, b, c, filler1)
 
 ANALYZE ndistinct;
 
-SELECT stxkind, stxndistinct
-  FROM pg_statistic_ext WHERE stxrelid = 'ndistinct'::regclass;
+SELECT s.stxkind, d.stxdndistinct
+  FROM pg_statistic_ext s, pg_statistic_ext_data d
+ WHERE s.stxrelid = 'ndistinct'::regclass
+   AND d.stxoid = s.oid;
 
 -- correct esimates
 SELECT * FROM check_estimated_rows('SELECT COUNT(*) FROM ndistinct GROUP BY a, b');
@@ -186,8 +190,10 @@ SELECT * FROM check_estimated_rows('SELECT COUNT(*) FROM ndistinct GROUP BY a, d
 
 DROP STATISTICS s10;
 
-SELECT stxkind, stxndistinct
-  FROM pg_statistic_ext WHERE stxrelid = 'ndistinct'::regclass;
+SELECT s.stxkind, d.stxdndistinct
+  FROM pg_statistic_ext s, pg_statistic_ext_data d
+ WHERE s.stxrelid = 'ndistinct'::regclass
+   AND d.stxoid = s.oid;
 
 -- dropping the statistics results in under-estimates
 SELECT * FROM check_estimated_rows('SELECT COUNT(*) FROM ndistinct GROUP BY a, b');
@@ -335,7 +341,10 @@ SELECT * FROM check_estimated_rows('SELECT * FROM mcv_lists WHERE a <= 4 AND b <
 -- check change of unrelated column type does not reset the MCV statistics
 ALTER TABLE mcv_lists ALTER COLUMN d TYPE VARCHAR(64);
 
-SELECT stxmcv IS NOT NULL FROM pg_statistic_ext WHERE stxname = 'mcv_lists_stats';
+SELECT d.stxdmcv IS NOT NULL
+  FROM pg_statistic_ext s, pg_statistic_ext_data d
+ WHERE s.stxname = 'mcv_lists_stats'
+   AND d.stxoid = s.oid;
 
 -- check change of column type resets the MCV statistics
 ALTER TABLE mcv_lists ALTER COLUMN c TYPE numeric;
@@ -378,8 +387,11 @@ TRUNCATE mcv_lists;
 INSERT INTO mcv_lists (a, b, c) SELECT 1, 2, 3 FROM generate_series(1,1000) s(i);
 ANALYZE mcv_lists;
 
-SELECT m.* FROM pg_statistic_ext,
-              pg_mcv_list_items(stxmcv) m WHERE stxname = 'mcv_lists_stats';
+SELECT m.*
+  FROM pg_statistic_ext s, pg_statistic_ext_data d,
+       pg_mcv_list_items(d.stxdmcv) m
+ WHERE s.stxname = 'mcv_lists_stats'
+   AND d.stxoid = s.oid;
 
 -- mcv with arrays
 CREATE TABLE mcv_lists_arrays (
diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
index 8cc033eb131..bdcbc8d15e0 100644
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -729,6 +729,7 @@ FormData_pg_sequence_data
 FormData_pg_shdepend
 FormData_pg_statistic
 FormData_pg_statistic_ext
+FormData_pg_statistic_ext_data
 FormData_pg_subscription
 FormData_pg_subscription_rel
 FormData_pg_tablespace
@@ -786,6 +787,7 @@ Form_pg_sequence_data
 Form_pg_shdepend
 Form_pg_statistic
 Form_pg_statistic_ext
+Form_pg_statistic_ext_data
 Form_pg_subscription
 Form_pg_subscription_rel
 Form_pg_tablespace