Use in-place updates for pg_restore_relation_stats().

This matches the behavior of vac_update_relstats(), which is important
to avoid bloating pg_class.

Author: Corey Huinker
Discussion: https://postgr.es/m/CADkLM=fc3je+ufv3gsHqjjSSf+t8674RXpuXW62EL55MUEQd-g@mail.gmail.com

doc/src/sgml/func.sgml

@@ -30175,6 +30175,14 @@ postgres=# SELECT '0/0'::pg_lsn + pd.segment_number * ps.setting::int + :offset
          function is to maintain a consistent function signature to avoid
          errors when restoring statistics from previous versions.
         </para>
+        <para>
+         To match the behavior of <xref linkend="sql-vacuum"/> and <xref
+         linkend="sql-analyze"/> when updating relation statistics,
+         <function>pg_restore_relation_stats()</function> does not follow MVCC
+         transactional semantics (see <xref linkend="mvcc"/>). New relation
+         statistics may be durable even if the transaction aborts, and the
+         changes are not isolated from other transactions.
+        </para>
         <para>
          Arguments are passed as pairs of <replaceable>argname</replaceable>
          and <replaceable>argvalue</replaceable>, where

src/backend/statistics/relation_stats.c

@@ -20,6 +20,7 @@
 #include "access/heapam.h"
 #include "catalog/indexing.h"
 #include "statistics/stat_utils.h"
+#include "utils/fmgroids.h"
 #include "utils/fmgrprotos.h"
 #include "utils/syscache.h"
 
@@ -50,25 +51,75 @@ static struct StatsArgInfo relarginfo[] =
 	[NUM_RELATION_STATS_ARGS] = {0}
 };
 
-static bool relation_statistics_update(FunctionCallInfo fcinfo, int elevel);
+static bool relation_statistics_update(FunctionCallInfo fcinfo, int elevel,
+									   bool inplace);
 
 /*
  * Internal function for modifying statistics for a relation.
  */
 static bool
-relation_statistics_update(FunctionCallInfo fcinfo, int elevel)
+relation_statistics_update(FunctionCallInfo fcinfo, int elevel, bool inplace)
 {
 	Oid			reloid;
 	Relation	crel;
-	HeapTuple	ctup;
+	int32		relpages = DEFAULT_RELPAGES;
-	Form_pg_class pgcform;
+	bool		update_relpages = false;
-	int			replaces[3] = {0};
+	float		reltuples = DEFAULT_RELTUPLES;
-	Datum		values[3] = {0};
+	bool		update_reltuples = false;
-	bool		nulls[3] = {0};
+	int32		relallvisible = DEFAULT_RELALLVISIBLE;
-	int			ncols = 0;
+	bool		update_relallvisible = false;
-	TupleDesc	tupdesc;
 	bool		result = true;
 
+	if (!PG_ARGISNULL(RELPAGES_ARG))
+	{
+		relpages = PG_GETARG_INT32(RELPAGES_ARG);
+
+		/*
+		 * Partitioned tables may have relpages=-1. Note: for relations with
+		 * no storage, relpages=-1 is not used consistently, but must be
+		 * supported here.
+		 */
+		if (relpages < -1)
+		{
+			ereport(elevel,
+					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+					 errmsg("relpages cannot be < -1")));
+			result = false;
+		}
+		else
+			update_relpages = true;
+	}
+
+	if (!PG_ARGISNULL(RELTUPLES_ARG))
+	{
+		reltuples = PG_GETARG_FLOAT4(RELTUPLES_ARG);
+
+		if (reltuples < -1.0)
+		{
+			ereport(elevel,
+					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+					 errmsg("reltuples cannot be < -1.0")));
+			result = false;
+		}
+		else
+			update_reltuples = true;
+	}
+
+	if (!PG_ARGISNULL(RELALLVISIBLE_ARG))
+	{
+		relallvisible = PG_GETARG_INT32(RELALLVISIBLE_ARG);
+
+		if (relallvisible < 0)
+		{
+			ereport(elevel,
+					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+					 errmsg("relallvisible cannot be < 0")));
+			result = false;
+		}
+		else
+			update_relallvisible = true;
+	}
+
 	stats_check_required_arg(fcinfo, relarginfo, RELATION_ARG);
 	reloid = PG_GETARG_OID(RELATION_ARG);
 
@@ -86,92 +137,99 @@ relation_statistics_update(FunctionCallInfo fcinfo, int elevel)
 	 */
 	crel = table_open(RelationRelationId, RowExclusiveLock);
 
-	tupdesc = RelationGetDescr(crel);
+	if (inplace)
-	ctup = SearchSysCacheCopy1(RELOID, ObjectIdGetDatum(reloid));
-	if (!HeapTupleIsValid(ctup))
 	{
-		ereport(elevel,
+		HeapTuple	ctup = NULL;
-				(errcode(ERRCODE_OBJECT_IN_USE),
+		ScanKeyData key[1];
-				 errmsg("pg_class entry for relid %u not found", reloid)));
+		Form_pg_class pgcform;
-		table_close(crel, RowExclusiveLock);
+		void	   *inplace_state = NULL;
-		return false;
+		bool		dirty = false;
+
+		ScanKeyInit(&key[0], Anum_pg_class_oid, BTEqualStrategyNumber, F_OIDEQ,
+					ObjectIdGetDatum(reloid));
+		systable_inplace_update_begin(crel, ClassOidIndexId, true, NULL, 1, key,
+									  &ctup, &inplace_state);
+		if (!HeapTupleIsValid(ctup))
+			elog(ERROR, "pg_class entry for relid %u vanished while updating statistics",
+				 reloid);
+		pgcform = (Form_pg_class) GETSTRUCT(ctup);
+
+		if (update_relpages && pgcform->relpages != relpages)
+		{
+			pgcform->relpages = relpages;
+			dirty = true;
+		}
+		if (update_reltuples && pgcform->reltuples != reltuples)
+		{
+			pgcform->reltuples = reltuples;
+			dirty = true;
+		}
+		if (update_relallvisible && pgcform->relallvisible != relallvisible)
+		{
+			pgcform->relallvisible = relallvisible;
+			dirty = true;
+		}
+
+		if (dirty)
+			systable_inplace_update_finish(inplace_state, ctup);
+		else
+			systable_inplace_update_cancel(inplace_state);
+
+		heap_freetuple(ctup);
 	}
-
+	else
-	pgcform = (Form_pg_class) GETSTRUCT(ctup);
-
-	/* relpages */
-	if (!PG_ARGISNULL(RELPAGES_ARG))
 	{
-		int32		relpages = PG_GETARG_INT32(RELPAGES_ARG);
+		TupleDesc	tupdesc = RelationGetDescr(crel);
+		HeapTuple	ctup;
+		Form_pg_class pgcform;
+		int			replaces[3] = {0};
+		Datum		values[3] = {0};
+		bool		nulls[3] = {0};
+		int			nreplaces = 0;
 
-		/*
+		ctup = SearchSysCache1(RELOID, ObjectIdGetDatum(reloid));
-		 * Partitioned tables may have relpages=-1. Note: for relations with
+		if (!HeapTupleIsValid(ctup))
-		 * no storage, relpages=-1 is not used consistently, but must be
-		 * supported here.
-		 */
-		if (relpages < -1)
 		{
 			ereport(elevel,
-					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+					(errcode(ERRCODE_OBJECT_IN_USE),
-					 errmsg("relpages cannot be < -1")));
+					 errmsg("pg_class entry for relid %u not found", reloid)));
-			result = false;
+			table_close(crel, RowExclusiveLock);
+			return false;
 		}
-		else if (relpages != pgcform->relpages)
+		pgcform = (Form_pg_class) GETSTRUCT(ctup);
+
+		if (update_relpages && relpages != pgcform->relpages)
 		{
-			replaces[ncols] = Anum_pg_class_relpages;
+			replaces[nreplaces] = Anum_pg_class_relpages;
-			values[ncols] = Int32GetDatum(relpages);
+			values[nreplaces] = Int32GetDatum(relpages);
-			ncols++;
+			nreplaces++;
 		}
-	}
 
-	if (!PG_ARGISNULL(RELTUPLES_ARG))
+		if (update_reltuples && reltuples != pgcform->reltuples)
-	{
-		float		reltuples = PG_GETARG_FLOAT4(RELTUPLES_ARG);
-
-		if (reltuples < -1.0)
 		{
-			ereport(elevel,
+			replaces[nreplaces] = Anum_pg_class_reltuples;
-					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+			values[nreplaces] = Float4GetDatum(reltuples);
-					 errmsg("reltuples cannot be < -1.0")));
+			nreplaces++;
-			result = false;
 		}
-		else if (reltuples != pgcform->reltuples)
+
+		if (update_relallvisible && relallvisible != pgcform->relallvisible)
 		{
-			replaces[ncols] = Anum_pg_class_reltuples;
+			replaces[nreplaces] = Anum_pg_class_relallvisible;
-			values[ncols] = Float4GetDatum(reltuples);
+			values[nreplaces] = Int32GetDatum(relallvisible);
-			ncols++;
+			nreplaces++;
 		}
 
-	}
+		if (nreplaces > 0)
-
-	if (!PG_ARGISNULL(RELALLVISIBLE_ARG))
-	{
-		int32		relallvisible = PG_GETARG_INT32(RELALLVISIBLE_ARG);
-
-		if (relallvisible < 0)
 		{
-			ereport(elevel,
+			HeapTuple	newtup;
-					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
-					 errmsg("relallvisible cannot be < 0")));
-			result = false;
-		}
-		else if (relallvisible != pgcform->relallvisible)
-		{
-			replaces[ncols] = Anum_pg_class_relallvisible;
-			values[ncols] = Int32GetDatum(relallvisible);
-			ncols++;
-		}
-	}
 
-	/* only update pg_class if there is a meaningful change */
+			newtup = heap_modify_tuple_by_cols(ctup, tupdesc, nreplaces,
-	if (ncols > 0)
+											   replaces, values, nulls);
-	{
+			CatalogTupleUpdate(crel, &newtup->t_self, newtup);
-		HeapTuple	newtup;
+			heap_freetuple(newtup);
+		}
 
-		newtup = heap_modify_tuple_by_cols(ctup, tupdesc, ncols, replaces, values,
+		ReleaseSysCache(ctup);
-										   nulls);
-		CatalogTupleUpdate(crel, &newtup->t_self, newtup);
-		heap_freetuple(newtup);
 	}
 
 	/* release the lock, consistent with vac_update_relstats() */
@@ -188,7 +246,7 @@ relation_statistics_update(FunctionCallInfo fcinfo, int elevel)
 Datum
 pg_set_relation_stats(PG_FUNCTION_ARGS)
 {
-	relation_statistics_update(fcinfo, ERROR);
+	relation_statistics_update(fcinfo, ERROR, false);
 	PG_RETURN_VOID();
 }
 
@@ -212,7 +270,7 @@ pg_clear_relation_stats(PG_FUNCTION_ARGS)
 	newfcinfo->args[3].value = DEFAULT_RELALLVISIBLE;
 	newfcinfo->args[3].isnull = false;
 
-	relation_statistics_update(newfcinfo, ERROR);
+	relation_statistics_update(newfcinfo, ERROR, false);
 	PG_RETURN_VOID();
 }
 
@@ -230,7 +288,7 @@ pg_restore_relation_stats(PG_FUNCTION_ARGS)
 										  relarginfo, WARNING))
 		result = false;
 
-	if (!relation_statistics_update(positional_fcinfo, WARNING))
+	if (!relation_statistics_update(positional_fcinfo, WARNING, true))
 		result = false;
 
 	PG_RETURN_BOOL(result);

src/test/regress/expected/stats_import.out

@@ -105,6 +105,47 @@ WHERE oid = 'stats_import.test'::regclass;
        18 |       401 |             5
 (1 row)
 
+-- test MVCC behavior: changes do not persist after abort (in contrast
+-- to pg_restore_relation_stats(), which uses in-place updates).
+BEGIN;
+SELECT
+    pg_catalog.pg_set_relation_stats(
+        relation => 'stats_import.test'::regclass,
+        relpages => NULL::integer,
+        reltuples => 4000.0::real,
+        relallvisible => 4::integer);
+ pg_set_relation_stats 
+-----------------------
+ 
+(1 row)
+
+ABORT;
+SELECT relpages, reltuples, relallvisible
+FROM pg_class
+WHERE oid = 'stats_import.test'::regclass;
+ relpages | reltuples | relallvisible 
+----------+-----------+---------------
+       18 |       401 |             5
+(1 row)
+
+BEGIN;
+SELECT
+    pg_catalog.pg_clear_relation_stats(
+        'stats_import.test'::regclass);
+ pg_clear_relation_stats 
+-------------------------
+ 
+(1 row)
+
+ABORT;
+SELECT relpages, reltuples, relallvisible
+FROM pg_class
+WHERE oid = 'stats_import.test'::regclass;
+ relpages | reltuples | relallvisible 
+----------+-----------+---------------
+       18 |       401 |             5
+(1 row)
+
 -- clear
 SELECT
     pg_catalog.pg_clear_relation_stats(
@@ -705,6 +746,25 @@ WHERE oid = 'stats_import.test'::regclass;
 (1 row)
 
 -- ok: just relpages
+SELECT pg_restore_relation_stats(
+        'relation', 'stats_import.test'::regclass,
+        'version', 150000::integer,
+        'relpages', '15'::integer);
+ pg_restore_relation_stats 
+---------------------------
+ t
+(1 row)
+
+SELECT relpages, reltuples, relallvisible
+FROM pg_class
+WHERE oid = 'stats_import.test'::regclass;
+ relpages | reltuples | relallvisible 
+----------+-----------+---------------
+       15 |       400 |             4
+(1 row)
+
+-- test non-MVCC behavior: new value should persist after abort
+BEGIN;
 SELECT pg_restore_relation_stats(
         'relation', 'stats_import.test'::regclass,
         'version', 150000::integer,
@@ -714,6 +774,7 @@ SELECT pg_restore_relation_stats(
  t
 (1 row)
 
+ABORT;
 SELECT relpages, reltuples, relallvisible
 FROM pg_class
 WHERE oid = 'stats_import.test'::regclass;

src/test/regress/sql/stats_import.sql

@@ -76,6 +76,31 @@ SELECT relpages, reltuples, relallvisible
 FROM pg_class
 WHERE oid = 'stats_import.test'::regclass;
 
+-- test MVCC behavior: changes do not persist after abort (in contrast
+-- to pg_restore_relation_stats(), which uses in-place updates).
+BEGIN;
+SELECT
+    pg_catalog.pg_set_relation_stats(
+        relation => 'stats_import.test'::regclass,
+        relpages => NULL::integer,
+        reltuples => 4000.0::real,
+        relallvisible => 4::integer);
+ABORT;
+
+SELECT relpages, reltuples, relallvisible
+FROM pg_class
+WHERE oid = 'stats_import.test'::regclass;
+
+BEGIN;
+SELECT
+    pg_catalog.pg_clear_relation_stats(
+        'stats_import.test'::regclass);
+ABORT;
+
+SELECT relpages, reltuples, relallvisible
+FROM pg_class
+WHERE oid = 'stats_import.test'::regclass;
+
 -- clear
 SELECT
     pg_catalog.pg_clear_relation_stats(
@@ -565,10 +590,22 @@ FROM pg_class
 WHERE oid = 'stats_import.test'::regclass;
 
 -- ok: just relpages
+SELECT pg_restore_relation_stats(
+        'relation', 'stats_import.test'::regclass,
+        'version', 150000::integer,
+        'relpages', '15'::integer);
+
+SELECT relpages, reltuples, relallvisible
+FROM pg_class
+WHERE oid = 'stats_import.test'::regclass;
+
+-- test non-MVCC behavior: new value should persist after abort
+BEGIN;
 SELECT pg_restore_relation_stats(
         'relation', 'stats_import.test'::regclass,
         'version', 150000::integer,
         'relpages', '16'::integer);
+ABORT;
 
 SELECT relpages, reltuples, relallvisible
 FROM pg_class