CREATE EXTENSION pg_buffercache;
select count(*) = (select setting::bigint
                   from pg_settings
                   where name = 'shared_buffers')
from pg_buffercache;
 ?column? 
----------
 t
(1 row)

select buffers_used + buffers_unused > 0,
        buffers_dirty <= buffers_used,
        buffers_pinned <= buffers_used
from pg_buffercache_summary();
 ?column? | ?column? | ?column? 
----------+----------+----------
 t        | t        | t
(1 row)

SELECT count(*) > 0 FROM pg_buffercache_usage_counts() WHERE buffers >= 0;
 ?column? 
----------
 t
(1 row)

-- Check that the functions / views can't be accessed by default. To avoid
-- having to create a dedicated user, use the pg_database_owner pseudo-role.
SET ROLE pg_database_owner;
SELECT * FROM pg_buffercache;
ERROR:  permission denied for view pg_buffercache
SELECT * FROM pg_buffercache_pages() AS p (wrong int);
ERROR:  permission denied for function pg_buffercache_pages
SELECT * FROM pg_buffercache_summary();
ERROR:  permission denied for function pg_buffercache_summary
SELECT * FROM pg_buffercache_usage_counts();
ERROR:  permission denied for function pg_buffercache_usage_counts
RESET role;
-- Check that pg_monitor is allowed to query view / function
SET ROLE pg_monitor;
SELECT count(*) > 0 FROM pg_buffercache;
 ?column? 
----------
 t
(1 row)

SELECT buffers_used + buffers_unused > 0 FROM pg_buffercache_summary();
 ?column? 
----------
 t
(1 row)

SELECT count(*) > 0 FROM pg_buffercache_usage_counts();
 ?column? 
----------
 t
(1 row)