Add pg_stat_session

Author: Sergey Dudoladov

Reviewed-by:

Discussion:
https://www.postgresql.org/message-id/flat/CA%2BFpmFcJF0vwi-SWW0wYO-c-FbhyawLq4tCpRDCJJ8Bq%3Dja-gA%40mail.gmail.com

Author: Sergey Dudoladov

doc/src/sgml/monitoring.sgml

@@ -414,6 +414,20 @@ postgres   27093  0.0  0.0  30096  2752 ?        Ss   11:34   0:00 postgres: ser
        See <xref linkend='copy-progress-reporting'/>.
       </entry>
      </row>
+
+     <row>
+      <entry>
+       <structname>pg_stat_session</structname>
+       <indexterm><primary>pg_stat_session</primary></indexterm>
+      </entry>
+      <entry>
+       One row per server process, showing information related to
+       the currently accumulated activity of that process, such as time spent in
+       a certain state.
+       See <link linkend="monitoring-pg-stat-session-view">
+       <structname>pg_stat_session</structname></link> for details.
+      </entry>
+     </row>
     </tbody>
    </tgroup>
   </table>
@@ -5261,6 +5275,53 @@ SELECT pid, wait_event_type, wait_event FROM pg_stat_activity WHERE wait_event i
    </tgroup>
   </table>
 
+  <table id="pg-stat-session-view" xreflabel="pg_stat_session">
+   <title><structname>pg_stat_session</structname> View</title>
+   <tgroup cols="1">
+    <thead>
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       Column Type
+      </para>
+      <para>
+       Description
+      </para></entry>
+     </row>
+    </thead>
+
+    <tbody>
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>pid</structfield> <type>integer</type>
+      </para>
+      <para>
+       Process ID of this backend
+      </para></entry>
+     </row>
+
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>total_active_time</structfield> <type>double precision</type>
+      </para>
+      <para>
+       Time in milliseconds this backend spent in <literal>active</literal> and
+       <literal>fastpath function call</literal> states.
+      </para></entry>
+     </row>
+
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>total_idle_in_transaction_time</structfield> <type>double precision</type>
+      </para>
+      <para>
+       Time in milliseconds this backend spent in <literal>idle in transaction</literal>
+       and <literal>idle in transaction (aborted)</literal> states.
+      </para></entry>
+     </row>
+    </tbody>
+   </tgroup>
+  </table>
+
  </sect2>
 
  <sect2 id="monitoring-stats-functions">
@@ -5328,6 +5389,22 @@ SELECT pid, wait_event_type, wait_event FROM pg_stat_activity WHERE wait_event i
        </para></entry>
       </row>
 
+      <row>
+       <entry role="func_table_entry"><para role="func_signature">
+        <indexterm>
+         <primary>pg_stat_get_session</primary>
+        </indexterm>
+        <function>pg_stat_get_session</function> ( <type>integer</type> )
+        <returnvalue>setof record</returnvalue>
+       </para>
+       <para>
+        Returns a record of information about the backend with the specified
+        process ID, or one record for each active backend in the system
+        if <literal>NULL</literal> is specified.  The fields returned are a
+        subset of those in the <structname>pg_stat_session</structname> view.
+       </para></entry>
+      </row>
+
       <row>
        <entry role="func_table_entry"><para role="func_signature">
         <indexterm>

src/backend/catalog/system_views.sql

@@ -871,6 +871,15 @@ CREATE VIEW pg_stat_activity AS
         LEFT JOIN pg_database AS D ON (S.datid = D.oid)
         LEFT JOIN pg_authid AS U ON (S.usesysid = U.oid);
 
+--CREATE VIEW pg_stat_session AS
+--    SELECT 
+--            S.pid,
+--            S.total_active_time,
+--            S.total_transaction_idle_time,
+--            S.total_transaction_idle_count
+--            S.total_active_count,
+--     FROM pg_stat_get_session(NULL) as S;
+
 CREATE VIEW pg_stat_replication AS
     SELECT
             S.pid,

src/backend/utils/activity/backend_status.c

@@ -338,6 +338,8 @@ pgstat_bestart(void)
 	lbeentry.st_xact_start_timestamp = 0;
 	lbeentry.st_databaseid = MyDatabaseId;
 
+	MemSet(&lbeentry.st_session, 0, sizeof(lbeentry.st_session));
+
 	/* We have userid for client-backends, wal-sender and bgworker processes */
 	if (lbeentry.st_backendType == B_BACKEND
 		|| lbeentry.st_backendType == B_WAL_SENDER
@@ -525,6 +527,9 @@ pgstat_report_activity(BackendState state, const char *cmd_str)
 	TimestampTz current_timestamp;
 	int			len = 0;
 
+	PgBackendSessionStatus st_session_diff;
+	MemSet(&st_session_diff, 0, sizeof(st_session_diff));
+
 	TRACE_POSTGRESQL_STATEMENT_STATUS(cmd_str);
 
 	if (!beentry)
@@ -550,6 +555,10 @@ pgstat_report_activity(BackendState state, const char *cmd_str)
 			beentry->st_xact_start_timestamp = 0;
 			beentry->st_query_id = UINT64CONST(0);
 			proc->wait_event_info = 0;
+			beentry->st_session.total_active_time = 0;
+			beentry->st_session.total_active_count = 0;
+			beentry->st_session.total_transaction_idle_time = 0;
+			beentry->st_session.total_transaction_idle_count = 0;
 			PGSTAT_END_WRITE_ACTIVITY(beentry);
 		}
 		return;
@@ -575,24 +584,40 @@ pgstat_report_activity(BackendState state, const char *cmd_str)
 	 * If the state has changed from "active" or "idle in transaction",
 	 * calculate the duration.
 	 */
-	if ((beentry->st_state == STATE_RUNNING ||
-		 beentry->st_state == STATE_FASTPATH ||
-		 beentry->st_state == STATE_IDLEINTRANSACTION ||
-		 beentry->st_state == STATE_IDLEINTRANSACTION_ABORTED) &&
+	if ((PGSTAT_IS_ACTIVE(beentry) || PGSTAT_IS_IDLEINTRANSACTION(beentry)) &&
 		state != beentry->st_state)
 	{
 		long		secs;
 		int			usecs;
+		int64		usecs_diff;
 
 		TimestampDifference(beentry->st_state_start_timestamp,
 							current_timestamp,
 							&secs, &usecs);
+		usecs_diff = secs * 1000000 + usecs;
 
-		if (beentry->st_state == STATE_RUNNING ||
-			beentry->st_state == STATE_FASTPATH)
+		if (PGSTAT_IS_ACTIVE(beentry))
 			pgstat_count_conn_active_time((PgStat_Counter) secs * 1000000 + usecs);
 		else
 			pgstat_count_conn_txn_idle_time((PgStat_Counter) secs * 1000000 + usecs);
+
+		/*
+		 * We update per-backend st_total_active_time and st_total_transaction_idle_time
+		 * separately from pgStatActiveTime and pgStatTransactionIdleTime
+		 * used in pg_stat_database to provide per-DB statistics because
+		 * 1. Changing the former values implies modifying beentry and thus
+		 * have to be wrapped into PGSTAT_*_WRITE_ACTIVITY macros (see below).
+		 * 2. The latter values are reset to 0 once the data has been sent
+		 * to the statistics collector.
+		 */
+		if (PGSTAT_IS_ACTIVE(beentry)) {
+			st_session_diff.total_active_time = usecs_diff;
+			st_session_diff.total_active_count += 1;
+		}
+		else {
+			st_session_diff.total_transaction_idle_time = usecs_diff;
+			st_session_diff.total_transaction_idle_count += 1;
+		}
 	}
 
 	/*
@@ -618,6 +643,12 @@ pgstat_report_activity(BackendState state, const char *cmd_str)
 		beentry->st_activity_start_timestamp = start_timestamp;
 	}
 
+	beentry->st_session.total_active_time += st_session_diff.total_active_time;
+	beentry->st_session.total_active_count += st_session_diff.total_active_count;
+
+	beentry->st_session.total_transaction_idle_time += st_session_diff.total_transaction_idle_time;
+	beentry->st_session.total_transaction_idle_count += st_session_diff.total_transaction_idle_count;
+
 	PGSTAT_END_WRITE_ACTIVITY(beentry);
 }
 

src/backend/utils/adt/pgstatfuncs.c

@@ -553,6 +553,55 @@ pg_stat_get_progress_info(PG_FUNCTION_ARGS)
 	return (Datum) 0;
 }
 
+/*
+ * Returns accumulated statistics of currently active PG backends.
+ */
+Datum
+pg_stat_get_session(PG_FUNCTION_ARGS)
+{
+#define PG_STAT_GET_SESSION_COLS	5
+	int			num_backends = pgstat_fetch_stat_numbackends();
+	int			curr_backend;
+	ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
+
+	InitMaterializedSRF(fcinfo, 0);
+
+	/* 1-based index */
+	for (curr_backend = 1; curr_backend <= num_backends; curr_backend++)
+	{
+		/* for each row */
+		Datum		values[PG_STAT_GET_SESSION_COLS] = {0};
+		bool		nulls[PG_STAT_GET_SESSION_COLS] = {0};
+		LocalPgBackendStatus *local_beentry;
+		PgBackendStatus *beentry;
+
+		/* Get the next one in the list */
+		local_beentry = pgstat_fetch_stat_local_beentry(curr_backend);
+		beentry = &local_beentry->backendStatus;
+
+		/* Values available to all callers */
+		values[0] = Int32GetDatum(beentry->st_procpid);
+
+		/* Values only available to role member or pg_read_all_stats */
+		if (HAS_PGSTAT_PERMISSIONS(beentry->st_userid)){
+			/* convert to msec */
+			values[1] = Float8GetDatum(beentry->st_session.total_active_time / 1000.0);
+			values[2] = Int64GetDatum(beentry->st_session.total_active_count);
+			values[3] = Float8GetDatum(beentry->st_session.total_transaction_idle_time / 1000.0);
+			values[4] = Int64GetDatum(beentry->st_session.total_transaction_idle_count);
+		} else {
+			nulls[1] = true;
+			nulls[2] = true;
+			nulls[3] = true;
+			nulls[4] = true;
+		}
+
+		tuplestore_putvalues(rsinfo->setResult, rsinfo->setDesc, values, nulls);
+	}
+
+	return (Datum) 0;
+}
+
 /*
  * Returns activity of PG backends.
  */

src/include/catalog/pg_proc.dat

@@ -5351,6 +5351,15 @@
   proargmodes => '{i,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o}',
   proargnames => '{pid,datid,pid,usesysid,application_name,state,query,wait_event_type,wait_event,xact_start,query_start,backend_start,state_change,client_addr,client_hostname,client_port,backend_xid,backend_xmin,backend_type,ssl,sslversion,sslcipher,sslbits,ssl_client_dn,ssl_client_serial,ssl_issuer_dn,gss_auth,gss_princ,gss_enc,leader_pid,query_id}',
   prosrc => 'pg_stat_get_activity' },
+{ oid => '2173',
+  descr => 'statistics: cumulative information about currently active backends',
+  proname => 'pg_stat_get_session', prorows => '100', proisstrict => 'f',
+  proretset => 't', provolatile => 's', proparallel => 'r',
+  prorettype => 'record', proargtypes => 'int4',
+  proallargtypes => '{int4,float8,int8,float8,int8}',
+  proargmodes => '{i,o,o,o,o}',
+  proargnames => '{pid,total_active_time,total_active_count,total_transaction_idle_time,total_transaction_idle_count}',
+  prosrc => 'pg_stat_get_session' },
 { oid => '3318',
   descr => 'statistics: information about progress of backends running maintenance command',
   proname => 'pg_stat_get_progress_info', prorows => '100', proretset => 't',

src/include/utils/backend_status.h

@@ -80,6 +80,22 @@ typedef struct PgBackendGSSStatus
 
 } PgBackendGSSStatus;
 
+/*
+ * PgBackendSessionStatus
+ *
+ * For each backend, we keep per-session cumulative counters in a within
+ * PgBackendStatus struct. The struct is always filled.
+ *
+ * All char arrays must be null-terminated.
+ */
+typedef struct PgBackendSessionStatus
+{
+	/* Counters accumulated since the start of the session */
+	int64		total_active_time;
+	int64		total_active_count;
+	int64		total_transaction_idle_time;
+	int64		total_transaction_idle_count;
+} PgBackendSessionStatus;
 
 /* ----------
  * PgBackendStatus
@@ -169,6 +185,9 @@ typedef struct PgBackendStatus
 
 	/* query identifier, optionally computed using post_parse_analyze_hook */
 	uint64		st_query_id;
+
+	/* Counters accumulated since the start of the session */
+	PgBackendSessionStatus st_session;
 } PgBackendStatus;
 
 
@@ -233,6 +252,14 @@ typedef struct PgBackendStatus
 	 ((before_changecount) & 1) == 0)
 
 
+/* Macros to identify the states for time accounting */
+#define PGSTAT_IS_ACTIVE(s) \
+	((s)->st_state == STATE_RUNNING || (s)->st_state == STATE_FASTPATH)
+#define PGSTAT_IS_IDLEINTRANSACTION(s) \
+	((s)->st_state == STATE_IDLEINTRANSACTION || \
+	 (s)->st_state == STATE_IDLEINTRANSACTION_ABORTED)
+
+
 /* ----------
  * LocalPgBackendStatus
  *

src/test/regress/expected/rules.out

@@ -2068,6 +2068,12 @@ pg_stat_replication_slots| SELECT s.slot_name,
    FROM pg_replication_slots r,
     LATERAL pg_stat_get_replication_slot((r.slot_name)::text) s(slot_name, spill_txns, spill_count, spill_bytes, stream_txns, stream_count, stream_bytes, total_txns, total_bytes, stats_reset)
   WHERE (r.datoid IS NOT NULL);
+pg_stat_session| SELECT s.pid,
+    s.total_active_time,
+    s.total_active_count,
+    s.total_transaction_idle_time,
+    s.total_transaction_idle_count
+   FROM pg_stat_get_session(NULL::integer) s(pid integer, total_active_time double precision, total_active_count integer, total_transaction_idle_time double precision, total_transaction_idle_count integer);
 pg_stat_slru| SELECT s.name,
     s.blks_zeroed,
     s.blks_hit,