Issue - (#2): Extended pg_stat_statement to provide new features.

Support for database/user/client based aggregates added to access
these statistics with three new views added. Some new counters added
including min/max/mean's time histograms. We are saving the parameters
of the slow queries, which can be tested later. Did some refactoring
of the code, by renaming the whole extension from pg_stat_statement to
pg_stat_monitor.

pg_stat_monitor--1.0.sql

@@ -0,0 +1,142 @@
+/* contrib/pg_stat_monitor/pg_stat_monitor--1.4.sql */
+
+-- complain if script is sourced in psql, rather than via CREATE EXTENSION
+\echo Use "CREATE EXTENSION pg_stat_monitor" to load this file. \quit
+
+-- Register functions.
+CREATE FUNCTION pg_stat_monitor_reset()
+RETURNS void
+AS 'MODULE_PATHNAME'
+LANGUAGE C PARALLEL SAFE;
+
+CREATE FUNCTION pg_stat_monitor(IN showtext boolean,
+    OUT userid oid,
+    OUT dbid oid,
+    OUT queryid bigint,
+    OUT query text,
+    OUT calls int8,
+    OUT total_time float8,
+    OUT min_time float8,
+    OUT max_time float8,
+    OUT mean_time float8,
+    OUT stddev_time float8,
+    OUT rows int8,
+    OUT shared_blks_hit int8,
+    OUT shared_blks_read int8,
+    OUT shared_blks_dirtied int8,
+    OUT shared_blks_written int8,
+    OUT local_blks_hit int8,
+    OUT local_blks_read int8,
+    OUT local_blks_dirtied int8,
+    OUT local_blks_written int8,
+    OUT temp_blks_read int8,
+    OUT temp_blks_written int8,
+    OUT blk_read_time float8,
+    OUT blk_write_time float8,
+    OUT host int,
+    OUT hist_calls text,
+    OUT hist_min_time text,
+    OUT hist_max_time text,
+    OUT hist_mean_time text,
+    OUT slow_query text,
+    OUT cpu_user_time float8,
+    OUT cpu_sys_time  float8
+)
+RETURNS SETOF record
+AS 'MODULE_PATHNAME', 'pg_stat_monitor_1_3'
+LANGUAGE C STRICT VOLATILE PARALLEL SAFE;
+
+CREATE FUNCTION pg_stat_agg(
+  OUT queryid bigint, 
+  OUT id bigint, 
+  OUT type bigint, 
+  OUT total_calls int,
+  OUT first_call_time timestamptz,
+  OUT last_call_time timestamptz)
+RETURNS SETOF record
+AS 'MODULE_PATHNAME', 'pg_stat_agg'
+LANGUAGE C STRICT VOLATILE PARALLEL SAFE;
+
+-- Register a view on the function for ease of use.
+CREATE VIEW pg_stat_monitor AS
+  SELECT * FROM pg_stat_monitor(true);
+
+GRANT SELECT ON pg_stat_monitor TO PUBLIC;
+
+CREATE VIEW pg_stat_agg_database AS
+SELECT
+  agg.queryid,
+  agg.id AS dbid,
+  ss.userid,
+  '0.0.0.0'::inet + ss.host AS host,
+  agg.total_calls,
+  ss.min_time,
+  ss.max_time,
+  ss.mean_time,
+  (string_to_array(hist_calls, ',')) hist_calls,
+  (string_to_array(hist_min_time, ',')) hist_min_time,
+  (string_to_array(hist_max_time, ',')) hist_max_time,
+  (string_to_array(hist_mean_time, ',')) hist_mean_time,
+  agg.first_call_time AS first_log_time,
+  agg.last_call_time AS last_log_time,
+  ss.cpu_user_time,
+  ss.cpu_sys_time,
+  ss.query,
+  ss.slow_query
+FROM pg_stat_agg() agg 
+INNER JOIN (SELECT DISTINCT queryid, userid, query, host, min_time, max_time, mean_time, hist_calls, hist_min_time, hist_max_time,hist_mean_time,slow_query,cpu_user_time,cpu_sys_time
+FROM pg_stat_monitor) ss 
+ON agg.queryid = ss.queryid AND agg.type = 0;
+
+CREATE VIEW pg_stat_agg_user AS
+SELECT
+  agg.queryid,
+  agg.id AS dbid,
+  ss.userid,
+  '0.0.0.0'::inet + ss.host AS host,
+  agg.total_calls,
+  ss.min_time,
+  ss.max_time,
+  ss.mean_time,
+  (string_to_array(hist_calls, ',')) hist_calls,
+  (string_to_array(hist_min_time, ',')) hist_min_time,
+  (string_to_array(hist_max_time, ',')) hist_max_time,
+  (string_to_array(hist_mean_time, ',')) hist_mean_time,
+  agg.first_call_time AS first_log_time,
+  agg.last_call_time AS last_log_time,
+  ss.cpu_user_time,
+  ss.cpu_sys_time,
+  ss.query,
+  ss.slow_query
+FROM pg_stat_agg() agg 
+INNER JOIN (SELECT DISTINCT queryid, userid, query, host, min_time, max_time, mean_time, hist_calls, hist_min_time, hist_max_time,hist_mean_time,slow_query,cpu_user_time,cpu_sys_time FROM pg_stat_monitor) ss 
+ON agg.queryid = ss.queryid AND agg.type = 1;
+
+CREATE VIEW pg_stat_agg_host AS
+SELECT
+  agg.queryid,
+  agg.id AS dbid,
+  ss.userid,
+  '0.0.0.0'::inet + ss.host AS host,
+  agg.total_calls,
+  ss.min_time,
+  ss.max_time,
+  ss.mean_time,
+  (string_to_array(hist_calls, ',')) hist_calls,
+  (string_to_array(hist_min_time, ',')) hist_min_time,
+  (string_to_array(hist_max_time, ',')) hist_max_time,
+  (string_to_array(hist_mean_time, ',')) hist_mean_time,
+  agg.first_call_time AS first_log_time,
+  agg.last_call_time AS last_log_time,
+  ss.cpu_user_time,
+  ss.cpu_sys_time,
+  ss.query,
+  ss.slow_query 
+FROM pg_stat_agg() agg 
+INNER JOIN (SELECT DISTINCT queryid, userid, query, host, min_time, max_time, mean_time, hist_calls, hist_min_time, hist_max_time,hist_mean_time,slow_query,cpu_user_time,cpu_sys_time FROM pg_stat_monitor) ss 
+ON agg.queryid = ss.queryid AND agg.type = 2;
+
+GRANT SELECT ON pg_stat_agg_database TO PUBLIC;
+
+-- Don't want this to be available to non-superusers.
+REVOKE ALL ON FUNCTION pg_stat_monitor_reset() FROM PUBLIC;