pgstattuple: Have pgstattuple_approx accept TOAST tables

TOAST tables have a visibility map and a free space map, so they can
be supported by pgstattuple_approx just fine.

Add test cases to show how various pgstattuple functions accept TOAST
tables.  Also add similar tests to pg_visibility, which already
accepted TOAST tables correctly but had no test coverage for them.
Reviewed-by: Laurenz Albe <laurenz.albe@cybertec.at>
Discussion: https://www.postgresql.org/message-id/flat/27c4496a-02b9-dc87-8f6f-bddbef54e0fe@2ndquadrant.com

contrib/pg_visibility/expected/pg_visibility.out

@@ -102,8 +102,9 @@ ERROR:  "test_foreign_table" is not a table, materialized view, or TOAST table
 select pg_truncate_visibility_map('test_foreign_table');
 ERROR:  "test_foreign_table" is not a table, materialized view, or TOAST table
 -- check some of the allowed relkinds
-create table regular_table (a int);
-insert into regular_table values (1), (2);
+create table regular_table (a int, b text);
+alter table regular_table alter column b set storage external;
+insert into regular_table values (1, repeat('one', 1000)), (2, repeat('two', 1000));
 vacuum regular_table;
 select count(*) > 0 from pg_visibility('regular_table');
  ?column? 
@@ -111,6 +112,12 @@ select count(*) > 0 from pg_visibility('regular_table');
  t
 (1 row)
 
+select count(*) > 0 from pg_visibility((select reltoastrelid from pg_class where relname = 'regular_table'));
+ ?column? 
+----------
+ t
+(1 row)
+
 truncate regular_table;
 select count(*) > 0 from pg_visibility('regular_table');
  ?column? 
@@ -118,6 +125,12 @@ select count(*) > 0 from pg_visibility('regular_table');
  f
 (1 row)
 
+select count(*) > 0 from pg_visibility((select reltoastrelid from pg_class where relname = 'regular_table'));
+ ?column? 
+----------
+ f
+(1 row)
+
 create materialized view matview_visibility_test as select * from regular_table;
 vacuum matview_visibility_test;
 select count(*) > 0 from pg_visibility('matview_visibility_test');

contrib/pg_visibility/sql/pg_visibility.sql

@@ -68,12 +68,15 @@ select pg_check_frozen('test_foreign_table');
 select pg_truncate_visibility_map('test_foreign_table');
 
 -- check some of the allowed relkinds
-create table regular_table (a int);
-insert into regular_table values (1), (2);
+create table regular_table (a int, b text);
+alter table regular_table alter column b set storage external;
+insert into regular_table values (1, repeat('one', 1000)), (2, repeat('two', 1000));
 vacuum regular_table;
 select count(*) > 0 from pg_visibility('regular_table');
+select count(*) > 0 from pg_visibility((select reltoastrelid from pg_class where relname = 'regular_table'));
 truncate regular_table;
 select count(*) > 0 from pg_visibility('regular_table');
+select count(*) > 0 from pg_visibility((select reltoastrelid from pg_class where relname = 'regular_table'));
 
 create materialized view matview_visibility_test as select * from regular_table;
 vacuum matview_visibility_test;

contrib/pgstattuple/expected/pgstattuple.out

@@ -159,7 +159,7 @@ ERROR:  "test_partitioned" (partitioned table) is not supported
 select pgstattuple('test_partitioned_index');
 ERROR:  "test_partitioned_index" (partitioned index) is not supported
 select pgstattuple_approx('test_partitioned');
-ERROR:  "test_partitioned" is not a table or materialized view
+ERROR:  "test_partitioned" is not a table, materialized view, or TOAST table
 select pg_relpages('test_partitioned');
 ERROR:  "test_partitioned" is not a table, index, materialized view, sequence, or TOAST table
 select pgstatindex('test_partitioned');
@@ -173,7 +173,7 @@ create view test_view as select 1;
 select pgstattuple('test_view');
 ERROR:  "test_view" (view) is not supported
 select pgstattuple_approx('test_view');
-ERROR:  "test_view" is not a table or materialized view
+ERROR:  "test_view" is not a table, materialized view, or TOAST table
 select pg_relpages('test_view');
 ERROR:  "test_view" is not a table, index, materialized view, sequence, or TOAST table
 select pgstatindex('test_view');
@@ -189,7 +189,7 @@ create foreign table test_foreign_table () server dummy_server;
 select pgstattuple('test_foreign_table');
 ERROR:  "test_foreign_table" (foreign table) is not supported
 select pgstattuple_approx('test_foreign_table');
-ERROR:  "test_foreign_table" is not a table or materialized view
+ERROR:  "test_foreign_table" is not a table, materialized view, or TOAST table
 select pg_relpages('test_foreign_table');
 ERROR:  "test_foreign_table" is not a table, index, materialized view, sequence, or TOAST table
 select pgstatindex('test_foreign_table');
@@ -218,6 +218,25 @@ select pg_relpages('test_partition');
            0
 (1 row)
 
+-- toast tables should work
+select pgstattuple((select reltoastrelid from pg_class where relname = 'test'));
+     pgstattuple     
+---------------------
+ (0,0,0,0,0,0,0,0,0)
+(1 row)
+
+select pgstattuple_approx((select reltoastrelid from pg_class where relname = 'test'));
+  pgstattuple_approx   
+-----------------------
+ (0,0,0,0,0,0,0,0,0,0)
+(1 row)
+
+select pg_relpages((select reltoastrelid from pg_class where relname = 'test'));
+ pg_relpages 
+-------------
+           0
+(1 row)
+
 -- not for the index calls though, of course
 select pgstatindex('test_partition');
 ERROR:  relation "test_partition" is not a btree index

contrib/pgstattuple/pgstatapprox.c

@@ -278,15 +278,15 @@ pgstattuple_approx_internal(Oid relid, FunctionCallInfo fcinfo)
 				 errmsg("cannot access temporary tables of other sessions")));
 
 	/*
-	 * We support only ordinary relations and materialised views, because we
-	 * depend on the visibility map and free space map for our estimates about
-	 * unscanned pages.
+	 * We support only relation kinds with a visibility map and a free space
+	 * map.
 	 */
 	if (!(rel->rd_rel->relkind == RELKIND_RELATION ||
-		  rel->rd_rel->relkind == RELKIND_MATVIEW))
+		  rel->rd_rel->relkind == RELKIND_MATVIEW ||
+		  rel->rd_rel->relkind == RELKIND_TOASTVALUE))
 		ereport(ERROR,
 				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-				 errmsg("\"%s\" is not a table or materialized view",
+				 errmsg("\"%s\" is not a table, materialized view, or TOAST table",
 						RelationGetRelationName(rel))));
 
 	if (rel->rd_rel->relam != HEAP_TABLE_AM_OID)

contrib/pgstattuple/sql/pgstattuple.sql

@@ -100,6 +100,11 @@ select pgstattuple('test_partition');
 select pgstattuple_approx('test_partition');
 select pg_relpages('test_partition');
 
+-- toast tables should work
+select pgstattuple((select reltoastrelid from pg_class where relname = 'test'));
+select pgstattuple_approx((select reltoastrelid from pg_class where relname = 'test'));
+select pg_relpages((select reltoastrelid from pg_class where relname = 'test'));
+
 -- not for the index calls though, of course
 select pgstatindex('test_partition');
 select pgstatginindex('test_partition');