Add pg_visibility contrib module.

This lets you examine the visibility map as well as page-level
visibility information.  I initially wrote it as a debugging aid,
but was encouraged to polish it for commit.

Patch by me, reviewed by Masahiko Sawada.

Discussion: 56D77803.6080503@BlueTreble.com

Author: robertmhaas

contrib/Makefile

@@ -37,6 +37,7 @@ SUBDIRS = \
 		pgcrypto	\
 		pgrowlocks	\
 		pgstattuple	\
+		pg_visibility	\
 		postgres_fdw	\
 		seg		\
 		spi		\

contrib/pg_visibility/Makefile

@@ -0,0 +1,19 @@
+# contrib/pg_visibility/Makefile
+
+MODULE_big = pg_visibility
+OBJS = pg_visibility.o $(WIN32RES)
+
+EXTENSION = pg_visibility
+DATA = pg_visibility--1.0.sql
+PGFILEDESC = "pg_visibility - page visibility information"
+
+ifdef USE_PGXS
+PG_CONFIG = pg_config
+PGXS := $(shell $(PG_CONFIG) --pgxs)
+include $(PGXS)
+else
+subdir = contrib/pg_visibility
+top_builddir = ../..
+include $(top_builddir)/src/Makefile.global
+include $(top_srcdir)/contrib/contrib-global.mk
+endif

contrib/pg_visibility/pg_visibility--1.0.sql

@@ -0,0 +1,52 @@
+/* contrib/pg_visibility/pg_visibility--1.0.sql */
+
+-- complain if script is sourced in psql, rather than via CREATE EXTENSION
+\echo Use "CREATE EXTENSION pg_visibility" to load this file. \quit
+
+-- Show visibility map information.
+CREATE FUNCTION pg_visibility_map(regclass, blkno bigint,
+								  all_visible OUT boolean,
+								  all_frozen OUT boolean)
+RETURNS record
+AS 'MODULE_PATHNAME', 'pg_visibility_map'
+LANGUAGE C STRICT;
+
+-- Show visibility map and page-level visibility information.
+CREATE FUNCTION pg_visibility(regclass, blkno bigint,
+							  all_visible OUT boolean,
+							  all_frozen OUT boolean,
+							  pd_all_visible OUT boolean)
+RETURNS record
+AS 'MODULE_PATHNAME', 'pg_visibility'
+LANGUAGE C STRICT;
+
+-- Show visibility map information for each block in a relation.
+CREATE FUNCTION pg_visibility_map(regclass, blkno OUT bigint,
+								  all_visible OUT boolean,
+								  all_frozen OUT boolean)
+RETURNS SETOF record
+AS 'MODULE_PATHNAME', 'pg_visibility_map_rel'
+LANGUAGE C STRICT;
+
+-- Show visibility map and page-level visibility information for each block.
+CREATE FUNCTION pg_visibility(regclass, blkno OUT bigint,
+							  all_visible OUT boolean,
+							  all_frozen OUT boolean,
+							  pd_all_visible OUT boolean)
+RETURNS SETOF record
+AS 'MODULE_PATHNAME', 'pg_visibility_rel'
+LANGUAGE C STRICT;
+
+-- Show summary of visibility map bits for a relation.
+CREATE FUNCTION pg_visibility_map_summary(regclass,
+    OUT all_visible bigint, OUT all_frozen bigint)
+RETURNS record
+AS 'MODULE_PATHNAME', 'pg_visibility_map_summary'
+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;