pg_buffercache: Add pg_buffercache_os_pages

ba2a3c2 has added a way to check if a buffer is spread across multiple pages with some NUMA information, via a new view pg_buffercache_numa that depends on pg_buffercache_numa_pages(), a SQL function. These can only be queried when support for libnuma exists, generating an error if not. However, it can be useful to know how shared buffers and OS pages map when NUMA is not supported or not available. This commit expands the capabilities around pg_buffercache_numa: - pg_buffercache_numa_pages() is refactored as an internal function, able to optionally process NUMA. Its SQL definition prior to this commit is still around to ensure backward-compatibility with v1.6. - A SQL function called pg_buffercache_os_pages() is added, able to work with or without NUMA. - The view pg_buffercache_numa is redefined to use pg_buffercache_os_pages(). - A new view is added, called pg_buffercache_os_pages. This ignores NUMA for its result processing, for a better efficiency. The implementation is done so as there is no code duplication between the NUMA and non-NUMA views/functions, relying on one internal function that does the job for all of them. The module is bumped to v1.7. Author: Bertrand Drouvot <bertranddrouvot.pg@gmail.com> Reviewed-by: Mircea Cadariu <cadariu.mircea@gmail.com> Reviewed-by: Michael Paquier <michael@paquier.xyz> Discussion: https://postgr.es/m/Z/fFA2heH6lpSLlt@ip-10-97-1-34.eu-west-3.compute.internal

Author: michaelpq

contrib/pg_buffercache/Makefile

@@ -9,7 +9,7 @@ EXTENSION = pg_buffercache
 DATA = pg_buffercache--1.2.sql pg_buffercache--1.2--1.3.sql \
 pg_buffercache--1.1--1.2.sql pg_buffercache--1.0--1.1.sql \
 pg_buffercache--1.3--1.4.sql pg_buffercache--1.4--1.5.sql \
-pg_buffercache--1.5--1.6.sql
+pg_buffercache--1.5--1.6.sql pg_buffercache--1.6--1.7.sql
 PGFILEDESC = "pg_buffercache - monitoring of shared buffer cache in real-time"
 
 REGRESS = pg_buffercache pg_buffercache_numa

contrib/pg_buffercache/expected/pg_buffercache.out

@@ -8,6 +8,16 @@ from pg_buffercache;
  t
 (1 row)
 
+-- For pg_buffercache_os_pages, we expect at least one entry for each buffer
+select count(*) >= (select setting::bigint
+ from pg_settings
+ where name = 'shared_buffers')
+from pg_buffercache_os_pages;
+ ?column? 
+----------
+ t
+(1 row)
+
 select buffers_used + buffers_unused > 0,
  buffers_dirty <= buffers_used,
  buffers_pinned <= buffers_used
@@ -28,6 +38,8 @@ SELECT count(*) > 0 FROM pg_buffercache_usage_counts() WHERE buffers >= 0;
 SET ROLE pg_database_owner;
 SELECT * FROM pg_buffercache;
 ERROR: permission denied for view pg_buffercache
+SELECT * FROM pg_buffercache_os_pages;
+ERROR: permission denied for view pg_buffercache_os_pages
 SELECT * FROM pg_buffercache_pages() AS p (wrong int);
 ERROR: permission denied for function pg_buffercache_pages
 SELECT * FROM pg_buffercache_summary();
@@ -43,6 +55,12 @@ SELECT count(*) > 0 FROM pg_buffercache;
  t
 (1 row)
 
+SELECT count(*) > 0 FROM pg_buffercache_os_pages;
+ ?column? 
+----------
+ t
+(1 row)
+
 SELECT buffers_used + buffers_unused > 0 FROM pg_buffercache_summary();
  ?column? 
 ----------

contrib/pg_buffercache/meson.build

@@ -24,6 +24,7 @@ install_data(
  'pg_buffercache--1.3--1.4.sql',
  'pg_buffercache--1.4--1.5.sql',
  'pg_buffercache--1.5--1.6.sql',
+ 'pg_buffercache--1.6--1.7.sql',
  'pg_buffercache.control',
  kwargs: contrib_data_args,
 )

contrib/pg_buffercache/pg_buffercache--1.6--1.7.sql

@@ -0,0 +1,33 @@
+/* contrib/pg_buffercache/pg_buffercache--1.6--1.7.sql */
+
+-- complain if script is sourced in psql, rather than via ALTER EXTENSION
+\echo Use "ALTER EXTENSION pg_buffercache UPDATE TO '1.7'" to load this file. \quit
+
+-- Function to retrieve information about OS pages, with optional NUMA
+-- information.
+CREATE FUNCTION pg_buffercache_os_pages(IN include_numa boolean,
+ OUT bufferid integer,
+ OUT os_page_num bigint,
+ OUT numa_node integer)
+RETURNS SETOF record
+AS 'MODULE_PATHNAME', 'pg_buffercache_os_pages'
+LANGUAGE C PARALLEL SAFE;
+
+-- View for OS page information, without NUMA.
+CREATE VIEW pg_buffercache_os_pages AS
+ SELECT bufferid, os_page_num
+ FROM pg_buffercache_os_pages(false);
+
+-- Re-create view for OS page information, with NUMA.
+DROP VIEW pg_buffercache_numa;
+CREATE VIEW pg_buffercache_numa AS
+ SELECT bufferid, os_page_num, numa_node
+ FROM pg_buffercache_os_pages(true);
+
+REVOKE ALL ON FUNCTION pg_buffercache_os_pages(boolean) FROM PUBLIC;
+REVOKE ALL ON pg_buffercache_os_pages FROM PUBLIC;
+REVOKE ALL ON pg_buffercache_numa FROM PUBLIC;
+
+GRANT EXECUTE ON FUNCTION pg_buffercache_os_pages(boolean) TO pg_monitor;
+GRANT SELECT ON pg_buffercache_os_pages TO pg_monitor;
+GRANT SELECT ON pg_buffercache_numa TO pg_monitor;

contrib/pg_buffercache/pg_buffercache.control

@@ -1,5 +1,5 @@
 # pg_buffercache extension
 comment = 'examine the shared buffer cache'
-default_version = '1.6'
+default_version = '1.7'
 module_pathname = '$libdir/pg_buffercache'
 relocatable = true