Delete SIGUSR2 based fault injection logic in walreceiver.

Regular fault injection doesn't work for mirrors. Hence, using SIGUSR2 signal
and on-disk file coupled with it just for testing a fault injection mechanism
was coded. This seems very hacky and intrusive, hence plan is to get rid of the
same. Most of the tests using this framework are found not useful as majority of
code is upstream. Even if needs testing, better alternative would be explored.

src/backend/replication/walreceiver.c

@@ -89,12 +89,6 @@ static uint32 recvOff = 0;
 static volatile sig_atomic_t got_SIGHUP = false;
 static volatile sig_atomic_t got_SIGTERM = false;
 
-/* Following flags should be strictly used for testing purposes ONLY */
-static volatile sig_atomic_t wait_before_rcv = false;
-static volatile sig_atomic_t wait_before_send = false;
-static volatile sig_atomic_t wait_before_send_ack = false;
-static volatile sig_atomic_t resume = false;
-
 /*
  * LogstreamResult indicates the byte positions that we have already
  * written/fsynced.
@@ -145,7 +139,6 @@ static void WalRcvSigHupHandler(SIGNAL_ARGS);
 static void WalRcvSigUsr1Handler(SIGNAL_ARGS);
 static void WalRcvShutdownHandler(SIGNAL_ARGS);
 static void WalRcvQuickDieHandler(SIGNAL_ARGS);
-static void WalRcvUsr2Handler(SIGNAL_ARGS);
 static void WalRcvCrashHandler(SIGNAL_ARGS);
 
 
@@ -196,7 +189,6 @@ WalReceiverMain(void)
 	volatile WalRcvData *walrcv = WalRcv;
 	TimestampTz last_recv_timestamp;
 	bool		ping_sent;
-	File		pid_file;
 	sigjmp_buf	local_sigjmp_buf;
 
 	/*
@@ -280,7 +272,7 @@ WalReceiverMain(void)
 	pqsignal(SIGALRM, SIG_IGN);
 	pqsignal(SIGPIPE, SIG_IGN);
 	pqsignal(SIGUSR1, WalRcvSigUsr1Handler);
-	pqsignal(SIGUSR2, WalRcvUsr2Handler);
+	pqsignal(SIGUSR2, SIG_IGN);
 
 	/* Reset some signals that are accepted by postmaster but not here */
 	pqsignal(SIGCHLD, SIG_DFL);
@@ -327,30 +319,7 @@ WalReceiverMain(void)
 
 	/* Establish the connection to the primary for XLOG streaming */
 	EnableWalRcvImmediateExit();
-
-	/*
-	 * (Testing Purpose) - Create a PID file under $PGDATA directory
-	 * This file existence is very temporary and will be removed once the WAL receiver
-	 * sets up successful connection. Verifying the presence of the PID file
-	 * helps to find if the WAL Receiver was actually started or not.
-	 * Again, This is just for testing purpose. With enhancements in future,
-	 * this change can/will go away.
-	 */
-	if ((pid_file = PathNameOpenFile("wal_rcv.pid", O_RDWR | O_CREAT| PG_BINARY, 0600)) < 0)
-	{
-		ereport(LOG,
-				(errcode_for_file_access(),
-				 errmsg("could not open file \"%s\" for reading: %m",
-						"wal_rcv.pid")));
-	}
-	else
-		FileClose(pid_file);
-
 	walrcv_connect(conninfo);
-
-	/* (Testing Purpose) - Now drop the PID file */
-	unlink("wal_rcv.pid");
-
 	DisableWalRcvImmediateExit();
 
 	/* Initialize LogstreamResult, reply_message */
@@ -492,21 +461,6 @@ WalReceiverMain(void)
 							break;
 						}
 
-						/* Perform suspend if signaled by an external entity (Testing Purpose) */
-						if (wait_before_rcv)
-						{
-							while(true)
-							{
-								if (resume)
-								{
-									resume = false;
-									break;
-								}
-								pg_usleep(5000);
-							}
-							wait_before_rcv = false;
-						}
-
 						len = walrcv_receive(0, &buf);
 					}
 
@@ -566,21 +520,6 @@ WalReceiverMain(void)
 						}
 					}
 
-					/* Perform suspend if signaled by an external entity (Testing Purpose) */
-					if (wait_before_send_ack)
-					{
-						while(true)
-						{
-							if (resume)
-							{
-								resume = false;
-								break;
-							}
-							pg_usleep(5000);
-						}
-						wait_before_send_ack = false;
-					}
-
 					XLogWalRcvSendReply(requestReply, requestReply);
 					XLogWalRcvSendHSFeedback(false);
 				}
@@ -770,55 +709,6 @@ WalRcvFetchTimeLineHistoryFiles(TimeLineID first, TimeLineID last)
 	}
 }
 
-/*
- * This is the handler for USR2 signal. Currently, it is used for testing
- * purposes. Normally, an external entity signals (USR2) the WAL receiver process
- * and based on the input from an external file on disk the WAL Receiver acts
- * upon that.
- */
-static void
-WalRcvUsr2Handler(SIGNAL_ARGS)
-{
-#define BUF_SIZE 80
-	File file;
-	int nbytes = 0;
-	char buf[BUF_SIZE];
-
-	/* Read the type of action to take later from the file in the $PGDATA */
-	if ((file = PathNameOpenFile("wal_rcv_test", O_RDONLY | PG_BINARY, 0600)) < 0)
-	{
-		/* Do not error out inside signal handler. Ignore it.*/
-		return;
-	}
-	else
-	{
-		nbytes = FileRead(file, buf, BUF_SIZE - 1);
-		if (nbytes <= 0)
-		{
-			/* Cleanup */
-			FileClose(file);
-
-			/* Don't error out. Ignore. */
-			return;
-		}
-		FileClose(file);
-
-		Assert(nbytes < BUF_SIZE);
-		buf[nbytes] = '\0';
-
-		if (strcmp(buf,"wait_before_send_ack") == 0)
-			wait_before_send_ack = true;
-		else if (strcmp(buf,"wait_before_rcv") == 0)
-			wait_before_rcv = true;
-		else if (strcmp(buf,"wait_before_send") == 0)
-			wait_before_send = true;
-		else if (strcmp(buf,"resume") == 0)
-			resume = true;
-		else
-			return;
-	}
-}
-
 /*
  * Mark us as STOPPED in shared memory at exit.
  */
@@ -1209,21 +1099,6 @@ XLogWalRcvSendReply(bool force, bool requestReply)
 	flushPtr = LogstreamResult.Flush;
 	applyPtr = GetXLogReplayRecPtr(NULL);
 
-	/* Perform suspend if signaled by an external entity (Testing Purpose) */
-	if (wait_before_send)
-	{
-		while(true)
-		{
-			if (resume)
-			{
-				resume = false;
-				break;
-			}
-			pg_usleep(5000);
-		}
-		wait_before_send = false;
-	}
-
 	resetStringInfo(&reply_message);
 	pq_sendbyte(&reply_message, 'r');
 	pq_sendint64(&reply_message, writePtr);