Fix inadequacies in recently added wait events

In commit 9915de6c1c, we introduced a new wait point for replication
slots and incorrectly labelled it as wait event PG_WAIT_LOCK.  That's
wrong, so invent an appropriate new wait event instead, and document it
properly.

While at it, fix numerous other problems in the vicinity:
- two different walreceiver wait events were being mixed up in a single
  wait event (which wasn't documented either); split it out so that they
  can be distinguished, and document the new events properly.

- ParallelBitmapPopulate was documented but didn't exist.

- ParallelBitmapScan was not documented (I think this should be called
  "ParallelBitmapScanInit" instead.)

- Logical replication wait events weren't documented

- various symbols had been added in dartboard order in various places.
  Put them in alphabetical order instead, as was originally intended.

Discussion: https://postgr.es/m/20170808181131.mu4fjepuh5m75cyq@alvherre.pgsql

src/backend/postmaster/pgstat.c

@@ -3481,6 +3481,12 @@ pgstat_get_wait_activity(WaitEventActivity w)
 		case WAIT_EVENT_CHECKPOINTER_MAIN:
 			event_name = "CheckpointerMain";
 			break;
+		case WAIT_EVENT_LOGICAL_LAUNCHER_MAIN:
+			event_name = "LogicalLauncherMain";
+			break;
+		case WAIT_EVENT_LOGICAL_APPLY_MAIN:
+			event_name = "LogicalApplyMain";
+			break;
 		case WAIT_EVENT_PGSTAT_MAIN:
 			event_name = "PgStatMain";
 			break;
@@ -3502,12 +3508,6 @@ pgstat_get_wait_activity(WaitEventActivity w)
 		case WAIT_EVENT_WAL_WRITER_MAIN:
 			event_name = "WalWriterMain";
 			break;
-		case WAIT_EVENT_LOGICAL_LAUNCHER_MAIN:
-			event_name = "LogicalLauncherMain";
-			break;
-		case WAIT_EVENT_LOGICAL_APPLY_MAIN:
-			event_name = "LogicalApplyMain";
-			break;
 			/* no default case, so that compiler will warn */
 	}
 
@@ -3533,15 +3533,18 @@ pgstat_get_wait_client(WaitEventClient w)
 		case WAIT_EVENT_CLIENT_WRITE:
 			event_name = "ClientWrite";
 			break;
+		case WAIT_EVENT_LIBPQWALRECEIVER_CONNECT:
+			event_name = "LibPQWalReceiverConnect";
+			break;
+		case WAIT_EVENT_LIBPQWALRECEIVER_RECEIVE:
+			event_name = "LibPQWalReceiverReceive";
+			break;
 		case WAIT_EVENT_SSL_OPEN_SERVER:
 			event_name = "SSLOpenServer";
 			break;
 		case WAIT_EVENT_WAL_RECEIVER_WAIT_START:
 			event_name = "WalReceiverWaitStart";
 			break;
-		case WAIT_EVENT_LIBPQWALRECEIVER:
-			event_name = "LibPQWalReceiver";
-			break;
 		case WAIT_EVENT_WAL_SENDER_WAIT_WAL:
 			event_name = "WalSenderWaitForWAL";
 			break;
@@ -3579,6 +3582,12 @@ pgstat_get_wait_ipc(WaitEventIPC w)
 		case WAIT_EVENT_EXECUTE_GATHER:
 			event_name = "ExecuteGather";
 			break;
+		case WAIT_EVENT_LOGICAL_SYNC_DATA:
+			event_name = "LogicalSyncData";
+			break;
+		case WAIT_EVENT_LOGICAL_SYNC_STATE_CHANGE:
+			event_name = "LogicalSyncStateChange";
+			break;
 		case WAIT_EVENT_MQ_INTERNAL:
 			event_name = "MessageQueueInternal";
 			break;
@@ -3600,18 +3609,15 @@ pgstat_get_wait_ipc(WaitEventIPC w)
 		case WAIT_EVENT_PROCARRAY_GROUP_UPDATE:
 			event_name = "ProcArrayGroupUpdate";
 			break;
+		case WAIT_EVENT_REPLICATION_SLOT_DROP:
+			event_name = "ReplicationSlotDrop";
+			break;
 		case WAIT_EVENT_SAFE_SNAPSHOT:
 			event_name = "SafeSnapshot";
 			break;
 		case WAIT_EVENT_SYNC_REP:
 			event_name = "SyncRep";
 			break;
-		case WAIT_EVENT_LOGICAL_SYNC_DATA:
-			event_name = "LogicalSyncData";
-			break;
-		case WAIT_EVENT_LOGICAL_SYNC_STATE_CHANGE:
-			event_name = "LogicalSyncStateChange";
-			break;
 			/* no default case, so that compiler will warn */
 	}
 

src/backend/replication/libpqwalreceiver/libpqwalreceiver.c

@@ -181,7 +181,7 @@ libpqrcv_connect(const char *conninfo, bool logical, const char *appname,
 							   WL_LATCH_SET | io_flag,
 							   PQsocket(conn->streamConn),
 							   0,
-							   WAIT_EVENT_LIBPQWALRECEIVER);
+							   WAIT_EVENT_LIBPQWALRECEIVER_CONNECT);
 
 		/* Emergency bailout? */
 		if (rc & WL_POSTMASTER_DEATH)
@@ -582,7 +582,7 @@ libpqrcv_PQexec(PGconn *streamConn, const char *query)
 								   WL_LATCH_SET,
 								   PQsocket(streamConn),
 								   0,
-								   WAIT_EVENT_LIBPQWALRECEIVER);
+								   WAIT_EVENT_LIBPQWALRECEIVER_RECEIVE);
 
 			/* Emergency bailout? */
 			if (rc & WL_POSTMASTER_DEATH)

src/backend/replication/slot.c

@@ -391,7 +391,8 @@ retry:
 							name, active_pid)));
 
 		/* Wait here until we get signaled, and then restart */
-		ConditionVariableSleep(&slot->active_cv, PG_WAIT_LOCK);
+		ConditionVariableSleep(&slot->active_cv,
+							   WAIT_EVENT_REPLICATION_SLOT_DROP);
 		ConditionVariableCancelSleep();
 		goto retry;
 	}