CREATE EXTENSION pg_buffercache;

select count(*) = (select setting::bigint
                   from pg_settings
                   where name = 'shared_buffers')
from pg_buffercache;

select buffers_used + buffers_unused > 0,
        buffers_dirty <= buffers_used,
        buffers_pinned <= buffers_used
from pg_buffercache_summary();

-- 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;
SELECT * FROM pg_buffercache_pages() AS p (wrong int);
SELECT * FROM pg_buffercache_summary();
RESET role;

-- Check that pg_monitor is allowed to query view / function
SET ROLE pg_monitor;
SELECT count(*) > 0 FROM pg_buffercache;
SELECT buffers_used + buffers_unused > 0 FROM pg_buffercache_summary();