Track last time for statistics reset on databases and bgwriter

Tracks one counter for each database, which is reset whenever
the statistics for any individual object inside the database is
reset, and one counter for the background writer.

Tomas Vondra, reviewed by Greg Smith

doc/src/sgml/monitoring.sgml

@@ -267,7 +267,7 @@ postgres: <replaceable>user</> <replaceable>database</> <replaceable>host</> <re
       by backends (that is, not by the background writer), how many times
       those backends had to execute their own fsync calls (normally the
       background writer handles those even when the backend does its own
-      write), and total buffers allocated.
+      write), total buffers allocated, and time of last statistics reset.
      </entry>
      </row>
 
@@ -278,9 +278,9 @@ postgres: <replaceable>user</> <replaceable>database</> <replaceable>host</> <re
       number of transactions committed and rolled back in that database,
       total disk blocks read, total buffer hits (i.e., block
       read requests avoided by finding the block already in buffer cache),
-      number of rows returned, fetched, inserted, updated and deleted, and
+      number of rows returned, fetched, inserted, updated and deleted, the
       total number of queries cancelled due to conflict with recovery (on
-      standby servers).
+      standby servers), and time of last statistics reset.
      </entry>
      </row>
 
@@ -662,6 +662,19 @@ postgres: <replaceable>user</> <replaceable>database</> <replaceable>host</> <re
       </entry>
      </row>
 
+     <row>
+      <entry><literal><function>pg_stat_get_db_stat_reset_time</function>(<type>oid</type>)</literal></entry>
+      <entry><type>timestamptz</type></entry>
+      <entry>
+       Time of the last statistics reset for the database.  Initialized to the
+       system time during the first connection to each database.  The reset time
+       is updated when you call <function>pg_stat_reset</function> on the
+       database, as well as upon execution of
+       <function>pg_stat_reset_single_table_counters</function> against any
+       table or index in it.
+      </entry>
+     </row>
+
      <row>
       <entry><literal><function>pg_stat_get_numscans</function>(<type>oid</type>)</literal></entry>
       <entry><type>bigint</type></entry>
@@ -1126,6 +1139,16 @@ postgres: <replaceable>user</> <replaceable>database</> <replaceable>host</> <re
       </entry>
      </row>
 
+     <row>
+      <entry><literal><function>pg_stat_get_bgwriter_stat_reset_time()</function></literal></entry>
+      <entry><type>timestamptz</type></entry>
+      <entry>
+        Time of the last statistics reset for the background writer, updated
+        when executing <function>pg_stat_reset_shared('bgwriter')</function>
+        on the database cluster.
+      </entry>
+     </row>
+
      <row>
       <entry><literal><function>pg_stat_get_buf_written_backend()</function></literal></entry>
       <entry><type>bigint</type></entry>

src/backend/catalog/system_views.sql

@@ -530,7 +530,8 @@ CREATE VIEW pg_stat_database AS
             pg_stat_get_db_tuples_inserted(D.oid) AS tup_inserted,
             pg_stat_get_db_tuples_updated(D.oid) AS tup_updated,
             pg_stat_get_db_tuples_deleted(D.oid) AS tup_deleted,
-            pg_stat_get_db_conflict_all(D.oid) AS conflicts
+            pg_stat_get_db_conflict_all(D.oid) AS conflicts,
+            pg_stat_get_db_stat_reset_time(D.oid) AS stats_reset
     FROM pg_database D;
 
 CREATE VIEW pg_stat_database_conflicts AS
@@ -577,7 +578,8 @@ CREATE VIEW pg_stat_bgwriter AS
         pg_stat_get_bgwriter_maxwritten_clean() AS maxwritten_clean,
         pg_stat_get_buf_written_backend() AS buffers_backend,
         pg_stat_get_buf_fsync_backend() AS buffers_backend_fsync,
-        pg_stat_get_buf_alloc() AS buffers_alloc;
+        pg_stat_get_buf_alloc() AS buffers_alloc,
+        pg_stat_get_bgwriter_stat_reset_time() AS stats_reset;
 
 CREATE VIEW pg_user_mappings AS
     SELECT

src/backend/postmaster/pgstat.c

@@ -3160,6 +3160,8 @@ pgstat_get_db_entry(Oid databaseid, bool create)
 		result->n_conflict_bufferpin = 0;
 		result->n_conflict_startup_deadlock = 0;
 
+		result->stat_reset_timestamp = GetCurrentTimestamp();
+
 		memset(&hash_ctl, 0, sizeof(hash_ctl));
 		hash_ctl.keysize = sizeof(Oid);
 		hash_ctl.entrysize = sizeof(PgStat_StatTabEntry);
@@ -3439,6 +3441,12 @@ pgstat_read_statsfile(Oid onlydb, bool permanent)
 	 */
 	memset(&globalStats, 0, sizeof(globalStats));
 
+	/*
+	 * Set the current timestamp (will be kept only in case we can't load an
+	 * existing statsfile.
+	 */
+	globalStats.stat_reset_timestamp = GetCurrentTimestamp();
+
 	/*
 	 * Try to open the status file. If it doesn't exist, the backends simply
 	 * return zero for anything and the collector simply starts from scratch
@@ -4052,6 +4060,8 @@ pgstat_recv_resetcounter(PgStat_MsgResetcounter *msg, int len)
 	dbentry->n_tuples_deleted = 0;
 	dbentry->last_autovac_time = 0;
 
+	dbentry->stat_reset_timestamp = GetCurrentTimestamp();
+
 	memset(&hash_ctl, 0, sizeof(hash_ctl));
 	hash_ctl.keysize = sizeof(Oid);
 	hash_ctl.entrysize = sizeof(PgStat_StatTabEntry);
@@ -4083,6 +4093,7 @@ pgstat_recv_resetsharedcounter(PgStat_MsgResetsharedcounter *msg, int len)
 	{
 		/* Reset the global background writer statistics for the cluster. */
 		memset(&globalStats, 0, sizeof(globalStats));
+		globalStats.stat_reset_timestamp = GetCurrentTimestamp();
 	}
 
 	/*
@@ -4107,6 +4118,8 @@ pgstat_recv_resetsinglecounter(PgStat_MsgResetsinglecounter *msg, int len)
 	if (!dbentry)
 		return;
 
+	/* Set the reset timestamp for the whole database */
+	dbentry->stat_reset_timestamp = GetCurrentTimestamp();
 
 	/* Remove object if it exists, ignore it if not */
 	if (msg->m_resettype == RESET_TABLE)

src/backend/utils/adt/pgstatfuncs.c

@@ -77,12 +77,14 @@ extern Datum pg_stat_get_db_conflict_snapshot(PG_FUNCTION_ARGS);
 extern Datum pg_stat_get_db_conflict_bufferpin(PG_FUNCTION_ARGS);
 extern Datum pg_stat_get_db_conflict_startup_deadlock(PG_FUNCTION_ARGS);
 extern Datum pg_stat_get_db_conflict_all(PG_FUNCTION_ARGS);
+extern Datum pg_stat_get_db_stat_reset_time(PG_FUNCTION_ARGS);
 
 extern Datum pg_stat_get_bgwriter_timed_checkpoints(PG_FUNCTION_ARGS);
 extern Datum pg_stat_get_bgwriter_requested_checkpoints(PG_FUNCTION_ARGS);
 extern Datum pg_stat_get_bgwriter_buf_written_checkpoints(PG_FUNCTION_ARGS);
 extern Datum pg_stat_get_bgwriter_buf_written_clean(PG_FUNCTION_ARGS);
 extern Datum pg_stat_get_bgwriter_maxwritten_clean(PG_FUNCTION_ARGS);
+extern Datum pg_stat_get_bgwriter_stat_reset_time(PG_FUNCTION_ARGS);
 extern Datum pg_stat_get_buf_written_backend(PG_FUNCTION_ARGS);
 extern Datum pg_stat_get_buf_fsync_backend(PG_FUNCTION_ARGS);
 extern Datum pg_stat_get_buf_alloc(PG_FUNCTION_ARGS);
@@ -1135,6 +1137,24 @@ pg_stat_get_db_tuples_deleted(PG_FUNCTION_ARGS)
 	PG_RETURN_INT64(result);
 }
 
+Datum
+pg_stat_get_db_stat_reset_time(PG_FUNCTION_ARGS)
+{
+	Oid			dbid = PG_GETARG_OID(0);
+	TimestampTz result;
+	PgStat_StatDBEntry *dbentry;
+
+	if ((dbentry = pgstat_fetch_stat_dbentry(dbid)) == NULL)
+		result = 0;
+	else
+		result = dbentry->stat_reset_timestamp;
+
+	if (result == 0)
+		PG_RETURN_NULL();
+	else
+		PG_RETURN_TIMESTAMPTZ(result);
+}
+
 Datum
 pg_stat_get_db_conflict_tablespace(PG_FUNCTION_ARGS)
 {
@@ -1260,6 +1280,12 @@ pg_stat_get_bgwriter_maxwritten_clean(PG_FUNCTION_ARGS)
 	PG_RETURN_INT64(pgstat_fetch_global()->maxwritten_clean);
 }
 
+Datum
+pg_stat_get_bgwriter_stat_reset_time(PG_FUNCTION_ARGS)
+{
+	PG_RETURN_TIMESTAMPTZ(pgstat_fetch_global()->stat_reset_timestamp);
+}
+
 Datum
 pg_stat_get_buf_written_backend(PG_FUNCTION_ARGS)
 {

src/include/catalog/catversion.h

@@ -53,6 +53,6 @@
  */
 
 /*							yyyymmddN */
-#define CATALOG_VERSION_NO	201102091
+#define CATALOG_VERSION_NO	201102101
 
 #endif

src/include/catalog/pg_proc.h

@@ -3131,6 +3131,8 @@ DATA(insert OID = 3069 (  pg_stat_get_db_conflict_startup_deadlock PGNSP PGUID 1
 DESCR("statistics: recovery conflicts in database caused by buffer deadlock");
 DATA(insert OID = 3070 (  pg_stat_get_db_conflict_all PGNSP PGUID 12 1 0 0 f f f t f s 1 0 20 "26" _null_ _null_ _null_ _null_ pg_stat_get_db_conflict_all _null_ _null_ _null_ ));
 DESCR("statistics: recovery conflicts in database");
+DATA(insert OID = 3074 (  pg_stat_get_db_stat_reset_time PGNSP PGUID 12 1 0 0 f f f t f s 1 0 1184 "26" _null_ _null_ _null_ _null_	pg_stat_get_db_stat_reset_time _null_ _null_ _null_ ));
+DESCR("statistics: last reset for a database");
 DATA(insert OID = 2769 ( pg_stat_get_bgwriter_timed_checkpoints PGNSP PGUID 12 1 0 0 f f f t f s 0 0 20 "" _null_ _null_ _null_ _null_ pg_stat_get_bgwriter_timed_checkpoints _null_ _null_ _null_ ));
 DESCR("statistics: number of timed checkpoints started by the bgwriter");
 DATA(insert OID = 2770 ( pg_stat_get_bgwriter_requested_checkpoints PGNSP PGUID 12 1 0 0 f f f t f s 0 0 20 "" _null_ _null_ _null_ _null_ pg_stat_get_bgwriter_requested_checkpoints _null_ _null_ _null_ ));
@@ -3141,6 +3143,8 @@ DATA(insert OID = 2772 ( pg_stat_get_bgwriter_buf_written_clean PGNSP PGUID 12 1
 DESCR("statistics: number of buffers written by the bgwriter for cleaning dirty buffers");
 DATA(insert OID = 2773 ( pg_stat_get_bgwriter_maxwritten_clean PGNSP PGUID 12 1 0 0 f f f t f s 0 0 20 "" _null_ _null_ _null_ _null_ pg_stat_get_bgwriter_maxwritten_clean _null_ _null_ _null_ ));
 DESCR("statistics: number of times the bgwriter stopped processing when it had written too many buffers while cleaning");
+DATA(insert OID = 3075 ( pg_stat_get_bgwriter_stat_reset_time PGNSP PGUID 12 1 0 0 f f f t f s 0 0 1184 "" _null_ _null_ _null_ _null_	pg_stat_get_bgwriter_stat_reset_time _null_ _null_ _null_ ));
+DESCR("statistics: last reset for the bgwriter");
 DATA(insert OID = 2775 ( pg_stat_get_buf_written_backend PGNSP PGUID 12 1 0 0 f f f t f s 0 0 20 "" _null_ _null_ _null_ _null_ pg_stat_get_buf_written_backend _null_ _null_ _null_ ));
 DESCR("statistics: number of buffers written by backends");
 DATA(insert OID = 3063 ( pg_stat_get_buf_fsync_backend PGNSP PGUID 12 1 0 0 f f f t f s 0 0 20 "" _null_ _null_ _null_ _null_ pg_stat_get_buf_fsync_backend _null_ _null_ _null_ ));

src/include/pgstat.h

@@ -484,7 +484,7 @@ typedef union PgStat_Msg
  * ------------------------------------------------------------
  */
 
-#define PGSTAT_FILE_FORMAT_ID	0x01A5BC98
+#define PGSTAT_FILE_FORMAT_ID	0x01A5BC99
 
 /* ----------
  * PgStat_StatDBEntry			The collector's data per database
@@ -508,6 +508,7 @@ typedef struct PgStat_StatDBEntry
 	PgStat_Counter n_conflict_snapshot;
 	PgStat_Counter n_conflict_bufferpin;
 	PgStat_Counter n_conflict_startup_deadlock;
+	TimestampTz stat_reset_timestamp;
 
 
 	/*
@@ -584,6 +585,7 @@ typedef struct PgStat_GlobalStats
 	PgStat_Counter buf_written_backend;
 	PgStat_Counter buf_fsync_backend;
 	PgStat_Counter buf_alloc;
+	TimestampTz stat_reset_timestamp;
 } PgStat_GlobalStats;
 
 

src/test/regress/expected/rules.out

@@ -1294,8 +1294,8 @@ SELECT viewname, definition FROM pg_views WHERE schemaname <> 'information_schem
  pg_stat_activity            | SELECT s.datid, d.datname, s.procpid, s.usesysid, u.rolname AS usename, s.application_name, s.client_addr, s.client_port, s.backend_start, s.xact_start, s.query_start, s.waiting, s.current_query FROM pg_database d, pg_stat_get_activity(NULL::integer) s(datid, procpid, usesysid, application_name, current_query, waiting, xact_start, query_start, backend_start, client_addr, client_port), pg_authid u WHERE ((s.datid = d.oid) AND (s.usesysid = u.oid));
  pg_stat_all_indexes         | SELECT c.oid AS relid, i.oid AS indexrelid, n.nspname AS schemaname, c.relname, i.relname AS indexrelname, pg_stat_get_numscans(i.oid) AS idx_scan, pg_stat_get_tuples_returned(i.oid) AS idx_tup_read, pg_stat_get_tuples_fetched(i.oid) AS idx_tup_fetch FROM (((pg_class c JOIN pg_index x ON ((c.oid = x.indrelid))) JOIN pg_class i ON ((i.oid = x.indexrelid))) LEFT JOIN pg_namespace n ON ((n.oid = c.relnamespace))) WHERE (c.relkind = ANY (ARRAY['r'::"char", 't'::"char"]));
  pg_stat_all_tables          | SELECT c.oid AS relid, n.nspname AS schemaname, c.relname, pg_stat_get_numscans(c.oid) AS seq_scan, pg_stat_get_tuples_returned(c.oid) AS seq_tup_read, (sum(pg_stat_get_numscans(i.indexrelid)))::bigint AS idx_scan, ((sum(pg_stat_get_tuples_fetched(i.indexrelid)))::bigint + pg_stat_get_tuples_fetched(c.oid)) AS idx_tup_fetch, pg_stat_get_tuples_inserted(c.oid) AS n_tup_ins, pg_stat_get_tuples_updated(c.oid) AS n_tup_upd, pg_stat_get_tuples_deleted(c.oid) AS n_tup_del, pg_stat_get_tuples_hot_updated(c.oid) AS n_tup_hot_upd, pg_stat_get_live_tuples(c.oid) AS n_live_tup, pg_stat_get_dead_tuples(c.oid) AS n_dead_tup, pg_stat_get_last_vacuum_time(c.oid) AS last_vacuum, pg_stat_get_last_autovacuum_time(c.oid) AS last_autovacuum, pg_stat_get_last_analyze_time(c.oid) AS last_analyze, pg_stat_get_last_autoanalyze_time(c.oid) AS last_autoanalyze, pg_stat_get_vacuum_count(c.oid) AS vacuum_count, pg_stat_get_autovacuum_count(c.oid) AS autovacuum_count, pg_stat_get_analyze_count(c.oid) AS analyze_count, pg_stat_get_autoanalyze_count(c.oid) AS autoanalyze_count FROM ((pg_class c LEFT JOIN pg_index i ON ((c.oid = i.indrelid))) LEFT JOIN pg_namespace n ON ((n.oid = c.relnamespace))) WHERE (c.relkind = ANY (ARRAY['r'::"char", 't'::"char"])) GROUP BY c.oid, n.nspname, c.relname;
- pg_stat_bgwriter            | SELECT pg_stat_get_bgwriter_timed_checkpoints() AS checkpoints_timed, pg_stat_get_bgwriter_requested_checkpoints() AS checkpoints_req, pg_stat_get_bgwriter_buf_written_checkpoints() AS buffers_checkpoint, pg_stat_get_bgwriter_buf_written_clean() AS buffers_clean, pg_stat_get_bgwriter_maxwritten_clean() AS maxwritten_clean, pg_stat_get_buf_written_backend() AS buffers_backend, pg_stat_get_buf_fsync_backend() AS buffers_backend_fsync, pg_stat_get_buf_alloc() AS buffers_alloc;
- pg_stat_database            | SELECT d.oid AS datid, d.datname, pg_stat_get_db_numbackends(d.oid) AS numbackends, pg_stat_get_db_xact_commit(d.oid) AS xact_commit, pg_stat_get_db_xact_rollback(d.oid) AS xact_rollback, (pg_stat_get_db_blocks_fetched(d.oid) - pg_stat_get_db_blocks_hit(d.oid)) AS blks_read, pg_stat_get_db_blocks_hit(d.oid) AS blks_hit, pg_stat_get_db_tuples_returned(d.oid) AS tup_returned, pg_stat_get_db_tuples_fetched(d.oid) AS tup_fetched, pg_stat_get_db_tuples_inserted(d.oid) AS tup_inserted, pg_stat_get_db_tuples_updated(d.oid) AS tup_updated, pg_stat_get_db_tuples_deleted(d.oid) AS tup_deleted, pg_stat_get_db_conflict_all(d.oid) AS conflicts FROM pg_database d;
+ pg_stat_bgwriter            | SELECT pg_stat_get_bgwriter_timed_checkpoints() AS checkpoints_timed, pg_stat_get_bgwriter_requested_checkpoints() AS checkpoints_req, pg_stat_get_bgwriter_buf_written_checkpoints() AS buffers_checkpoint, pg_stat_get_bgwriter_buf_written_clean() AS buffers_clean, pg_stat_get_bgwriter_maxwritten_clean() AS maxwritten_clean, pg_stat_get_buf_written_backend() AS buffers_backend, pg_stat_get_buf_fsync_backend() AS buffers_backend_fsync, pg_stat_get_buf_alloc() AS buffers_alloc, pg_stat_get_bgwriter_stat_reset_time() AS stats_reset;
+ pg_stat_database            | SELECT d.oid AS datid, d.datname, pg_stat_get_db_numbackends(d.oid) AS numbackends, pg_stat_get_db_xact_commit(d.oid) AS xact_commit, pg_stat_get_db_xact_rollback(d.oid) AS xact_rollback, (pg_stat_get_db_blocks_fetched(d.oid) - pg_stat_get_db_blocks_hit(d.oid)) AS blks_read, pg_stat_get_db_blocks_hit(d.oid) AS blks_hit, pg_stat_get_db_tuples_returned(d.oid) AS tup_returned, pg_stat_get_db_tuples_fetched(d.oid) AS tup_fetched, pg_stat_get_db_tuples_inserted(d.oid) AS tup_inserted, pg_stat_get_db_tuples_updated(d.oid) AS tup_updated, pg_stat_get_db_tuples_deleted(d.oid) AS tup_deleted, pg_stat_get_db_conflict_all(d.oid) AS conflicts, pg_stat_get_db_stat_reset_time(d.oid) AS stats_reset FROM pg_database d;
  pg_stat_database_conflicts  | SELECT d.oid AS datid, d.datname, pg_stat_get_db_conflict_tablespace(d.oid) AS confl_tablespace, pg_stat_get_db_conflict_lock(d.oid) AS confl_lock, pg_stat_get_db_conflict_snapshot(d.oid) AS confl_snapshot, pg_stat_get_db_conflict_bufferpin(d.oid) AS confl_bufferpin, pg_stat_get_db_conflict_startup_deadlock(d.oid) AS confl_deadlock FROM pg_database d;
  pg_stat_replication         | SELECT s.procpid, s.usesysid, u.rolname AS usename, s.application_name, s.client_addr, s.client_port, s.backend_start, w.state, w.sent_location FROM pg_stat_get_activity(NULL::integer) s(datid, procpid, usesysid, application_name, current_query, waiting, xact_start, query_start, backend_start, client_addr, client_port), pg_authid u, pg_stat_get_wal_senders() w(procpid, state, sent_location) WHERE ((s.usesysid = u.oid) AND (s.procpid = w.procpid));
  pg_stat_sys_indexes         | SELECT pg_stat_all_indexes.relid, pg_stat_all_indexes.indexrelid, pg_stat_all_indexes.schemaname, pg_stat_all_indexes.relname, pg_stat_all_indexes.indexrelname, pg_stat_all_indexes.idx_scan, pg_stat_all_indexes.idx_tup_read, pg_stat_all_indexes.idx_tup_fetch FROM pg_stat_all_indexes WHERE ((pg_stat_all_indexes.schemaname = ANY (ARRAY['pg_catalog'::name, 'information_schema'::name])) OR (pg_stat_all_indexes.schemaname ~ '^pg_toast'::text));