Add ProcArrayGroupUpdate wait event.

Discussion: http://postgr.es/m/CA+TgmobgWHcXDcChX2+BqJDk2dkPVF85ZrJFhUyHHQmw8diTpA@mail.gmail.com

doc/src/sgml/monitoring.sgml

@@ -1232,7 +1232,7 @@ 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="11"><literal>IPC</></entry>
+         <entry morerows="12"><literal>IPC</></entry>
          <entry><literal>BgWorkerShutdown</></entry>
          <entry>Waiting for background worker to shut down.</entry>
         </row>
@@ -1272,6 +1272,9 @@ postgres   27093  0.0  0.0  30096  2752 ?        Ss   11:34   0:00 postgres: ser
          <entry><literal>ParallelBitmapPopulate</></entry>
          <entry>Waiting for the leader to populate the TidBitmap.</entry>
         </row>
+        <row>
+         <entry><literal>ProcArrayGroupUpdate</></entry>
+         <entry>Waiting for group leader to clear transaction id at transaction end.</entry>
         <row>
          <entry><literal>SafeSnapshot</></entry>
          <entry>Waiting for a snapshot for a <literal>READ ONLY DEFERRABLE</> transaction.</entry>

src/backend/postmaster/pgstat.c

@@ -3560,6 +3560,9 @@ pgstat_get_wait_ipc(WaitEventIPC w)
 		case WAIT_EVENT_PARALLEL_BITMAP_SCAN:
 			event_name = "ParallelBitmapScan";
 			break;
+		case WAIT_EVENT_PROCARRAY_GROUP_UPDATE:
+			event_name = "ProcArrayGroupUpdate";
+			break;
 		case WAIT_EVENT_SAFE_SNAPSHOT:
 			event_name = "SafeSnapshot";
 			break;

src/backend/storage/ipc/procarray.c

@@ -53,6 +53,7 @@
 #include "access/xlog.h"
 #include "catalog/catalog.h"
 #include "miscadmin.h"
+#include "pgstat.h"
 #include "storage/proc.h"
 #include "storage/procarray.h"
 #include "storage/spin.h"
@@ -513,6 +514,7 @@ ProcArrayGroupClearXid(PGPROC *proc, TransactionId latestXid)
 		int			extraWaits = 0;
 
 		/* Sleep until the leader clears our XID. */
+		pgstat_report_wait_start(WAIT_EVENT_PROCARRAY_GROUP_UPDATE);
 		for (;;)
 		{
 			/* acts as a read barrier */
@@ -521,6 +523,7 @@ ProcArrayGroupClearXid(PGPROC *proc, TransactionId latestXid)
 				break;
 			extraWaits++;
 		}
+		pgstat_report_wait_end();
 
 		Assert(pg_atomic_read_u32(&proc->procArrayGroupNext) == INVALID_PGPROCNO);
 

src/include/pgstat.h

@@ -808,6 +808,7 @@ typedef enum
 	WAIT_EVENT_MQ_SEND,
 	WAIT_EVENT_PARALLEL_FINISH,
 	WAIT_EVENT_PARALLEL_BITMAP_SCAN,
+	WAIT_EVENT_PROCARRAY_GROUP_UPDATE,
 	WAIT_EVENT_SAFE_SNAPSHOT,
 	WAIT_EVENT_SYNC_REP,
 	WAIT_EVENT_LOGICAL_SYNC_DATA,