Add integrity-checking functions to pg_visibility.

The new pg_check_visible() and pg_check_frozen() functions can be used to
verify that the visibility map bits for a relation's data pages match the
actual state of the tuples on those pages.

Amit Kapila and Robert Haas, reviewed (in earlier versions) by Andres
Freund.  Additional testing help by Thomas Munro.

Author: robertmhaas

contrib/pg_visibility/Makefile

@@ -4,7 +4,7 @@ MODULE_big = pg_visibility
 OBJS = pg_visibility.o $(WIN32RES)
 
 EXTENSION = pg_visibility
-DATA = pg_visibility--1.0.sql
+DATA = pg_visibility--1.1.sql pg_visibility--1.0--1.1.sql
 PGFILEDESC = "pg_visibility - page visibility information"
 
 ifdef USE_PGXS

contrib/pg_visibility/pg_visibility--1.0--1.1.sql

@@ -0,0 +1,17 @@
+/* contrib/pg_visibility/pg_visibility--1.0--1.1.sql */
+
+-- complain if script is sourced in psql, rather than via ALTER EXTENSION
+\echo Use "ALTER EXTENSION pg_visibility UPDATE TO '1.1'" to load this file. \quit
+
+CREATE FUNCTION pg_check_frozen(regclass, t_ctid OUT tid)
+RETURNS SETOF tid
+AS 'MODULE_PATHNAME', 'pg_check_frozen'
+LANGUAGE C STRICT;
+
+CREATE FUNCTION pg_check_visible(regclass, t_ctid OUT tid)
+RETURNS SETOF tid
+AS 'MODULE_PATHNAME', 'pg_check_visible'
+LANGUAGE C STRICT;
+
+REVOKE ALL ON FUNCTION pg_check_frozen(regclass) FROM PUBLIC;
+REVOKE ALL ON FUNCTION pg_check_visible(regclass) FROM PUBLIC;

contrib/pg_visibility/pg_visibility--1.0.sql renamed to contrib/pg_visibility/pg_visibility--1.1.sql

@@ -1,4 +1,4 @@
-/* contrib/pg_visibility/pg_visibility--1.0.sql */
+/* contrib/pg_visibility/pg_visibility--1.1.sql */
 
 -- complain if script is sourced in psql, rather than via CREATE EXTENSION
 \echo Use "CREATE EXTENSION pg_visibility" to load this file. \quit
@@ -44,9 +44,24 @@ RETURNS record
 AS 'MODULE_PATHNAME', 'pg_visibility_map_summary'
 LANGUAGE C STRICT;
 
+-- Show tupleids of non-frozen tuples if any in all_frozen pages
+-- for a relation.
+CREATE FUNCTION pg_check_frozen(regclass, t_ctid OUT tid)
+RETURNS SETOF tid
+AS 'MODULE_PATHNAME', 'pg_check_frozen'
+LANGUAGE C STRICT;
+
+-- Show tupleids of dead tuples if any in all_visible pages for a relation.
+CREATE FUNCTION pg_check_visible(regclass, t_ctid OUT tid)
+RETURNS SETOF tid
+AS 'MODULE_PATHNAME', 'pg_check_visible'
+LANGUAGE C STRICT;
+
 -- Don't want these to be available to public.
 REVOKE ALL ON FUNCTION pg_visibility_map(regclass, bigint) FROM PUBLIC;
 REVOKE ALL ON FUNCTION pg_visibility(regclass, bigint) FROM PUBLIC;
 REVOKE ALL ON FUNCTION pg_visibility_map(regclass) FROM PUBLIC;
 REVOKE ALL ON FUNCTION pg_visibility(regclass) FROM PUBLIC;
 REVOKE ALL ON FUNCTION pg_visibility_map_summary(regclass) FROM PUBLIC;
+REVOKE ALL ON FUNCTION pg_check_frozen(regclass) FROM PUBLIC;
+REVOKE ALL ON FUNCTION pg_check_visible(regclass) FROM PUBLIC;