Change the type of WalReceiverWaitStart wait event from Client to IPC.

Previously the type of this wait event was Client. But while this
wait event is being reported, walreceiver process is waiting for
the startup process to set initial data for streaming replication.
It's not waiting for any activity on a socket connected to a user
application or walsender. So this commit changes the type for
WalReceiverWaitStart wait event to IPC.

Author: Fujii Masao
Reviewed-by: Kyotaro Horiguchi
Discussion: https://postgr.es/m/cdacc27c-37ff-f1a4-20e2-ce19933abfcc@oss.nttdata.com

doc/src/sgml/monitoring.sgml

@@ -1171,11 +1171,6 @@ postgres   27093  0.0  0.0  30096  2752 ?        Ss   11:34   0:00 postgres: ser
       <entry><literal>SSLOpenServer</literal></entry>
       <entry>Waiting for SSL while attempting connection.</entry>
      </row>
-     <row>
-      <entry><literal>WalReceiverWaitStart</literal></entry>
-      <entry>Waiting for startup process to send initial data for streaming
-       replication.</entry>
-     </row>
      <row>
       <entry><literal>WalSenderWaitForWAL</literal></entry>
       <entry>Waiting for WAL to be flushed in WAL sender process.</entry>
@@ -1771,6 +1766,11 @@ postgres   27093  0.0  0.0  30096  2752 ?        Ss   11:34   0:00 postgres: ser
       <entry><literal>WalrcvExit</literal></entry>
       <entry>Waiting for the walreceiver to exit.</entry>
      </row>
+     <row>
+      <entry><literal>WalReceiverWaitStart</literal></entry>
+      <entry>Waiting for startup process to send initial data for streaming
+       replication.</entry>
+     </row>
      <row>
       <entry><literal>XactGroupUpdate</literal></entry>
       <entry>Waiting for the group leader to update transaction status at

src/backend/postmaster/pgstat.c

@@ -3970,9 +3970,6 @@ pgstat_get_wait_client(WaitEventClient w)
 		case WAIT_EVENT_SSL_OPEN_SERVER:
 			event_name = "SSLOpenServer";
 			break;
-		case WAIT_EVENT_WAL_RECEIVER_WAIT_START:
-			event_name = "WalReceiverWaitStart";
-			break;
 		case WAIT_EVENT_WAL_SENDER_WAIT_WAL:
 			event_name = "WalSenderWaitForWAL";
 			break;
@@ -4127,6 +4124,9 @@ pgstat_get_wait_ipc(WaitEventIPC w)
 		case WAIT_EVENT_WALRCV_EXIT:
 			event_name = "WalrcvExit";
 			break;
+		case WAIT_EVENT_WAL_RECEIVER_WAIT_START:
+			event_name = "WalReceiverWaitStart";
+			break;
 		case WAIT_EVENT_XACT_GROUP_UPDATE:
 			event_name = "XactGroupUpdate";
 			break;

src/include/pgstat.h

@@ -953,7 +953,6 @@ typedef enum
 	WAIT_EVENT_LIBPQWALRECEIVER_CONNECT,
 	WAIT_EVENT_LIBPQWALRECEIVER_RECEIVE,
 	WAIT_EVENT_SSL_OPEN_SERVER,
-	WAIT_EVENT_WAL_RECEIVER_WAIT_START,
 	WAIT_EVENT_WAL_SENDER_WAIT_WAL,
 	WAIT_EVENT_WAL_SENDER_WRITE_DATA,
 } WaitEventClient;
@@ -1010,6 +1009,7 @@ typedef enum
 	WAIT_EVENT_SAFE_SNAPSHOT,
 	WAIT_EVENT_SYNC_REP,
 	WAIT_EVENT_WALRCV_EXIT,
+	WAIT_EVENT_WAL_RECEIVER_WAIT_START,
 	WAIT_EVENT_XACT_GROUP_UPDATE
 } WaitEventIPC;