New system view pg_stat_replication displays activity of wal sender processes.

Itagaki Takahiro and Simon Riggs.

src/backend/catalog/system_views.sql

@@ -492,6 +492,21 @@ CREATE VIEW pg_stat_activity AS
     WHERE S.datid = D.oid AND
             S.usesysid = U.oid;
 
+CREATE VIEW pg_stat_replication AS
+    SELECT
+            S.procpid,
+            S.usesysid,
+            U.rolname AS usename,
+            S.application_name,
+            S.client_addr,
+            S.client_port,
+            S.backend_start,
+            W.sent_location
+    FROM pg_stat_get_activity(NULL) AS S, pg_authid U,
+            pg_stat_get_wal_senders() AS W
+    WHERE S.usesysid = U.oid AND
+            S.procpid = W.procpid;
+
 CREATE VIEW pg_stat_database AS
     SELECT
             D.oid AS datid,

src/backend/replication/walsender.c

@@ -37,6 +37,7 @@
 #include <signal.h>
 #include <unistd.h>
 
+#include "funcapi.h"
 #include "access/xlog_internal.h"
 #include "catalog/pg_type.h"
 #include "libpq/libpq.h"
@@ -49,6 +50,7 @@
 #include "storage/ipc.h"
 #include "storage/pmsignal.h"
 #include "tcop/tcopprot.h"
+#include "utils/builtins.h"
 #include "utils/guc.h"
 #include "utils/memutils.h"
 #include "utils/ps_status.h"
@@ -942,6 +944,78 @@ WalSndWakeup(void)
 		SetLatch(&WalSndCtl->walsnds[i].latch);
 }
 
+/*
+ * Returns activity of walsenders, including pids and xlog locations sent to
+ * standby servers.
+ */
+Datum
+pg_stat_get_wal_senders(PG_FUNCTION_ARGS)
+{
+#define PG_STAT_GET_WAL_SENDERS_COLS 	2
+	ReturnSetInfo	   *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
+	TupleDesc			tupdesc;
+	Tuplestorestate	   *tupstore;
+	MemoryContext		per_query_ctx;
+	MemoryContext		oldcontext;
+	int					i;
+
+	/* check to see if caller supports us returning a tuplestore */
+	if (rsinfo == NULL || !IsA(rsinfo, ReturnSetInfo))
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("set-valued function called in context that cannot accept a set")));
+	if (!(rsinfo->allowedModes & SFRM_Materialize))
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("materialize mode required, but it is not " \
+						"allowed in this context")));
+
+	/* Build a tuple descriptor for our result type */
+	if (get_call_result_type(fcinfo, NULL, &tupdesc) != TYPEFUNC_COMPOSITE)
+		elog(ERROR, "return type must be a row type");
+
+	per_query_ctx = rsinfo->econtext->ecxt_per_query_memory;
+	oldcontext = MemoryContextSwitchTo(per_query_ctx);
+
+	tupstore = tuplestore_begin_heap(true, false, work_mem);
+	rsinfo->returnMode = SFRM_Materialize;
+	rsinfo->setResult = tupstore;
+	rsinfo->setDesc = tupdesc;
+
+	MemoryContextSwitchTo(oldcontext);
+
+	for (i = 0; i < max_wal_senders; i++)
+	{
+		/* use volatile pointer to prevent code rearrangement */
+		volatile WalSnd *walsnd = &WalSndCtl->walsnds[i];
+		char		sent_location[MAXFNAMELEN];
+		XLogRecPtr	sentPtr;
+		Datum		values[PG_STAT_GET_WAL_SENDERS_COLS];
+		bool		nulls[PG_STAT_GET_WAL_SENDERS_COLS];
+
+		if (walsnd->pid == 0)
+			continue;
+
+		SpinLockAcquire(&walsnd->mutex);
+		sentPtr = walsnd->sentPtr;
+		SpinLockRelease(&walsnd->mutex);
+
+		snprintf(sent_location, sizeof(sent_location), "%X/%X",
+					sentPtr.xlogid, sentPtr.xrecoff);
+
+		memset(nulls, 0, sizeof(nulls));
+		values[0] = Int32GetDatum(walsnd->pid);
+		values[1] = CStringGetTextDatum(sent_location);
+
+		tuplestore_putvalues(tupstore, tupdesc, values, nulls);
+	}
+
+	/* clean up and return the tuplestore */
+	tuplestore_donestoring(tupstore);
+
+	return (Datum) 0;
+}
+
 /*
  * This isn't currently used for anything. Monitoring tools might be
  * interested in the future, and we'll need something like this in the

src/include/catalog/pg_proc.h

@@ -3075,6 +3075,8 @@ DATA(insert OID = 1936 (  pg_stat_get_backend_idset		PGNSP PGUID 12 1 100 0 f f
 DESCR("statistics: currently active backend IDs");
 DATA(insert OID = 2022 (  pg_stat_get_activity			PGNSP PGUID 12 1 100 0 f f f f t s 1 0 2249 "23" "{23,26,23,26,25,25,16,1184,1184,1184,869,23}" "{i,o,o,o,o,o,o,o,o,o,o,o}" "{pid,datid,procpid,usesysid,application_name,current_query,waiting,xact_start,query_start,backend_start,client_addr,client_port}" _null_ pg_stat_get_activity _null_ _null_ _null_ ));
 DESCR("statistics: information about currently active backends");
+DATA(insert OID = 3099 (  pg_stat_get_wal_senders	PGNSP PGUID 12 1 10 0 f f f f t s 0 0 2249 "" "{23,25}" "{o,o}" "{procpid,sent_location}" _null_ pg_stat_get_wal_senders _null_ _null_ _null_ ));
+DESCR("statistics: information about currently active replication");
 DATA(insert OID = 2026 (  pg_backend_pid				PGNSP PGUID 12 1 0 0 f f f t f s 0 0 23 "" _null_ _null_ _null_ _null_ pg_backend_pid _null_ _null_ _null_ ));
 DESCR("statistics: current backend PID");
 DATA(insert OID = 1937 (  pg_stat_get_backend_pid		PGNSP PGUID 12 1 0 0 f f f t f s 1 0 23 "23" _null_ _null_ _null_ _null_ pg_stat_get_backend_pid _null_ _null_ _null_ ));

src/include/replication/walsender.h

@@ -54,4 +54,6 @@ extern Size WalSndShmemSize(void);
 extern void WalSndShmemInit(void);
 extern void WalSndWakeup(void);
 
+extern Datum pg_stat_get_wal_senders(PG_FUNCTION_ARGS);
+
 #endif   /* _WALSENDER_H */

src/test/regress/expected/rules.out

@@ -1296,6 +1296,7 @@ SELECT viewname, definition FROM pg_views WHERE schemaname <> 'information_schem
  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_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.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, 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));
  pg_stat_sys_tables          | SELECT pg_stat_all_tables.relid, pg_stat_all_tables.schemaname, pg_stat_all_tables.relname, pg_stat_all_tables.seq_scan, pg_stat_all_tables.seq_tup_read, pg_stat_all_tables.idx_scan, pg_stat_all_tables.idx_tup_fetch, pg_stat_all_tables.n_tup_ins, pg_stat_all_tables.n_tup_upd, pg_stat_all_tables.n_tup_del, pg_stat_all_tables.n_tup_hot_upd, pg_stat_all_tables.n_live_tup, pg_stat_all_tables.n_dead_tup, pg_stat_all_tables.last_vacuum, pg_stat_all_tables.last_autovacuum, pg_stat_all_tables.last_analyze, pg_stat_all_tables.last_autoanalyze, pg_stat_all_tables.vacuum_count, pg_stat_all_tables.autovacuum_count, pg_stat_all_tables.analyze_count, pg_stat_all_tables.autoanalyze_count FROM pg_stat_all_tables WHERE ((pg_stat_all_tables.schemaname = ANY (ARRAY['pg_catalog'::name, 'information_schema'::name])) OR (pg_stat_all_tables.schemaname ~ '^pg_toast'::text));
  pg_stat_user_functions      | SELECT p.oid AS funcid, n.nspname AS schemaname, p.proname AS funcname, pg_stat_get_function_calls(p.oid) AS calls, (pg_stat_get_function_time(p.oid) / 1000) AS total_time, (pg_stat_get_function_self_time(p.oid) / 1000) AS self_time FROM (pg_proc p LEFT JOIN pg_namespace n ON ((n.oid = p.pronamespace))) WHERE ((p.prolang <> (12)::oid) AND (pg_stat_get_function_calls(p.oid) IS NOT NULL));
@@ -1335,7 +1336,7 @@ SELECT viewname, definition FROM pg_views WHERE schemaname <> 'information_schem
  shoelace_obsolete           | SELECT shoelace.sl_name, shoelace.sl_avail, shoelace.sl_color, shoelace.sl_len, shoelace.sl_unit, shoelace.sl_len_cm FROM shoelace WHERE (NOT (EXISTS (SELECT shoe.shoename FROM shoe WHERE (shoe.slcolor = shoelace.sl_color))));
  street                      | SELECT r.name, r.thepath, c.cname FROM ONLY road r, real_city c WHERE (c.outline ## r.thepath);
  toyemp                      | SELECT emp.name, emp.age, emp.location, (12 * emp.salary) AS annualsal FROM emp;
-(57 rows)
+(58 rows)
 
 SELECT tablename, rulename, definition FROM pg_rules
 	ORDER BY tablename, rulename;