Add wait events for WAL archive and recovery pause.

This commit introduces new wait events BackupWaitWalArchive and
RecoveryPause. The former is reported while waiting for the WAL files
required for the backup to be successfully archived. The latter is
reported while waiting for recovery in pause state to be resumed.

Author: Fujii Masao
Reviewed-by: Michael Paquier, Atsushi Torikoshi, Robert Haas
Discussion: https://postgr.es/m/f0651f8c-9c96-9f29-0ff9-80414a15308a@oss.nttdata.com

doc/src/sgml/monitoring.sgml

@@ -1339,7 +1339,11 @@ postgres   27093  0.0  0.0  30096  2752 ?        Ss   11:34   0:00 postgres: ser
          <entry>Waiting in an extension.</entry>
         </row>
         <row>
-         <entry morerows="36"><literal>IPC</literal></entry>
+         <entry morerows="38"><literal>IPC</literal></entry>
+         <entry><literal>BackupWaitWalArchive</literal></entry>
+         <entry>Waiting for WAL files required for the backup to be successfully archived.</entry>
+        </row>
+        <row>
          <entry><literal>BgWorkerShutdown</literal></entry>
          <entry>Waiting for background worker to shut down.</entry>
         </row>
@@ -1471,6 +1475,10 @@ postgres   27093  0.0  0.0  30096  2752 ?        Ss   11:34   0:00 postgres: ser
          <entry><literal>Promote</literal></entry>
          <entry>Waiting for standby promotion.</entry>
         </row>
+        <row>
+         <entry><literal>RecoveryPause</literal></entry>
+         <entry>Waiting for recovery to be resumed.</entry>
+        </row>
         <row>
          <entry><literal>ReplicationOriginDrop</literal></entry>
          <entry>Waiting for a replication origin to become inactive to be dropped.</entry>

src/backend/access/transam/xlog.c

@@ -5946,7 +5946,9 @@ recoveryPausesHere(void)
 
 	while (RecoveryIsPaused())
 	{
+		pgstat_report_wait_start(WAIT_EVENT_RECOVERY_PAUSE);
 		pg_usleep(1000000L);	/* 1000 ms */
+		pgstat_report_wait_end();
 		HandleStartupProcInterrupts();
 	}
 }
@@ -11146,7 +11148,9 @@ do_pg_stop_backup(char *labelfile, bool waitforarchive, TimeLineID *stoptli_p)
 				reported_waiting = true;
 			}
 
+			pgstat_report_wait_start(WAIT_EVENT_BACKUP_WAIT_WAL_ARCHIVE);
 			pg_usleep(1000000L);
+			pgstat_report_wait_end();
 
 			if (++waits >= seconds_before_warning)
 			{

src/backend/postmaster/pgstat.c

@@ -3682,6 +3682,9 @@ pgstat_get_wait_ipc(WaitEventIPC w)
 
 	switch (w)
 	{
+		case WAIT_EVENT_BACKUP_WAIT_WAL_ARCHIVE:
+			event_name = "BackupWaitWalArchive";
+			break;
 		case WAIT_EVENT_BGWORKER_SHUTDOWN:
 			event_name = "BgWorkerShutdown";
 			break;
@@ -3781,6 +3784,9 @@ pgstat_get_wait_ipc(WaitEventIPC w)
 		case WAIT_EVENT_PROMOTE:
 			event_name = "Promote";
 			break;
+		case WAIT_EVENT_RECOVERY_PAUSE:
+			event_name = "RecoveryPause";
+			break;
 		case WAIT_EVENT_REPLICATION_ORIGIN_DROP:
 			event_name = "ReplicationOriginDrop";
 			break;

src/include/pgstat.h

@@ -798,7 +798,8 @@ typedef enum
  */
 typedef enum
 {
-	WAIT_EVENT_BGWORKER_SHUTDOWN = PG_WAIT_IPC,
+	WAIT_EVENT_BACKUP_WAIT_WAL_ARCHIVE = PG_WAIT_IPC,
+	WAIT_EVENT_BGWORKER_SHUTDOWN,
 	WAIT_EVENT_BGWORKER_STARTUP,
 	WAIT_EVENT_BTREE_PAGE,
 	WAIT_EVENT_CLOG_GROUP_UPDATE,
@@ -831,6 +832,7 @@ typedef enum
 	WAIT_EVENT_PARALLEL_FINISH,
 	WAIT_EVENT_PROCARRAY_GROUP_UPDATE,
 	WAIT_EVENT_PROMOTE,
+	WAIT_EVENT_RECOVERY_PAUSE,
 	WAIT_EVENT_REPLICATION_ORIGIN_DROP,
 	WAIT_EVENT_REPLICATION_SLOT_DROP,
 	WAIT_EVENT_SAFE_SNAPSHOT,