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

6 files changed, 70 insertions, 12 deletions

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,