CREATE EXTENSION pg_stat_statements;
CREATE EXTENSION pg_stat_kcache;
-- first make sure that catcache is loaded to avoid physical reads
SELECT count(*) >= 0 FROM pg_stat_kcache;
 ?column? 
----------
 t
(1 row)

SELECT pg_stat_kcache_reset();
 pg_stat_kcache_reset 
----------------------
 
(1 row)

-- dummy query
SELECT 1 AS dummy;
 dummy 
-------
     1
(1 row)

SELECT count(*) FROM pg_stat_kcache WHERE datname = current_database();
 count 
-------
     1
(1 row)

SELECT count(*) FROM pg_stat_kcache_detail WHERE datname = current_database() AND (query = 'SELECT $1 AS dummy' OR query = 'SELECT ? AS dummy;');
 count 
-------
     1
(1 row)

SELECT exec_reads, exec_reads_blks, exec_writes, exec_writes_blks
FROM pg_stat_kcache_detail
WHERE datname = current_database()
AND (query = 'SELECT $1 AS dummy' OR query = 'SELECT ? AS dummy;');
 exec_reads | exec_reads_blks | exec_writes | exec_writes_blks 
------------+-----------------+-------------+------------------
          0 |               0 |           0 |                0
(1 row)

-- dummy table
CREATE TABLE test AS SELECT i FROM generate_series(1, 1000) i;
-- dummy query again
SELECT count(*) FROM test;
 count 
-------
  1000
(1 row)

SELECT exec_user_time + exec_system_time > 0 AS cpu_time_ok
FROM pg_stat_kcache_detail
WHERE datname = current_database()
AND query LIKE 'SELECT count(*) FROM test%';
 cpu_time_ok 
-------------
 t
(1 row)

-- dummy nested query
SET pg_stat_statements.track = 'all';
SET pg_stat_statements.track_planning = TRUE;
SET pg_stat_kcache.track = 'all';
SET pg_stat_kcache.track_planning = TRUE;
SELECT pg_stat_kcache_reset();
 pg_stat_kcache_reset 
----------------------
 
(1 row)

CREATE OR REPLACE FUNCTION plpgsql_nested()
  RETURNS void AS $$
BEGIN
  PERFORM i::text as str from generate_series(1, 100) as i;
  PERFORM md5(i::text) as str from generate_series(1, 100) as i;
END
$$ LANGUAGE plpgsql;
SELECT plpgsql_nested();
 plpgsql_nested 
----------------
 
(1 row)

SELECT COUNT(*) FROM pg_stat_kcache_detail WHERE top IS FALSE;
 count 
-------
     2
(1 row)