Put the logic to wait for WAL in standby mode to a separate function.

This is just refactoring with no user-visible effect, to make the code more
readable.

src/backend/access/transam/xlog.c

@@ -157,6 +157,9 @@ HotStandbyState standbyState = STANDBY_DISABLED;
 
 static XLogRecPtr LastRec;
 
+/* Local copy of WalRcv->receivedUpto */
+static XLogRecPtr receivedUpto = 0;
+
 /*
  * During recovery, lastFullPageWrites keeps track of full_page_writes that
  * the replayed WAL records indicate. It's initialized with full_page_writes
@@ -538,6 +541,7 @@ static int	readFile = -1;
 static XLogSegNo readSegNo = 0;
 static uint32 readOff = 0;
 static uint32 readLen = 0;
+static bool	readFileHeaderValidated = false;
 static int	readSource = 0;		/* XLOG_FROM_* code */
 
 /*
@@ -628,6 +632,8 @@ static int XLogFileRead(XLogSegNo segno, int emode, TimeLineID tli,
 static int XLogFileReadAnyTLI(XLogSegNo segno, int emode, int sources);
 static bool XLogPageRead(XLogRecPtr *RecPtr, int emode, bool fetching_ckpt,
 			 bool randAccess);
+static bool WaitForWALToBecomeAvailable(XLogRecPtr RecPtr, bool randAccess,
+							bool fetching_ckpt);
 static int	emode_for_corrupt_record(int emode, XLogRecPtr RecPtr);
 static void XLogFileClose(void);
 static void PreallocXlogFiles(XLogRecPtr endptr);
@@ -2685,6 +2691,9 @@ XLogFileRead(XLogSegNo segno, int emode, TimeLineID tli,
 		if (source != XLOG_FROM_STREAM)
 			XLogReceiptTime = GetCurrentTimestamp();
 
+		/* The file header needs to be validated on first access */
+		readFileHeaderValidated = false;
+
 		return fd;
 	}
 	if (errno != ENOENT || !notfoundOk) /* unexpected failure? */
@@ -9233,12 +9242,9 @@ static bool
 XLogPageRead(XLogRecPtr *RecPtr, int emode, bool fetching_ckpt,
 			 bool randAccess)
 {
-	static XLogRecPtr receivedUpto = 0;
-	bool		switched_segment = false;
 	uint32		targetPageOff;
 	uint32		targetRecOff;
 	XLogSegNo	targetSegNo;
-	static pg_time_t last_fail_time = 0;
 
 	XLByteToSeg(*RecPtr, targetSegNo);
 	targetPageOff = (((*RecPtr) % XLogSegSize) / XLOG_BLCKSZ) * XLOG_BLCKSZ;
@@ -9283,11 +9289,155 @@ retry:
 	{
 		if (StandbyMode)
 		{
+			if (!WaitForWALToBecomeAvailable(*RecPtr, randAccess,
+											 fetching_ckpt))
+				goto triggered;
+		}
+		else
+		{
+			/* In archive or crash recovery. */
+			if (readFile < 0)
+			{
+				int			sources;
+
+				/* Reset curFileTLI if random fetch. */
+				if (randAccess)
+					curFileTLI = 0;
+
+				sources = XLOG_FROM_PG_XLOG;
+				if (InArchiveRecovery)
+					sources |= XLOG_FROM_ARCHIVE;
+
+				readFile = XLogFileReadAnyTLI(readSegNo, emode, sources);
+				if (readFile < 0)
+					return false;
+			}
+		}
+	}
+
+	/*
+	 * At this point, we have the right segment open and if we're streaming we
+	 * know the requested record is in it.
+	 */
+	Assert(readFile != -1);
+
+	/*
+	 * If the current segment is being streamed from master, calculate how
+	 * much of the current page we have received already. We know the
+	 * requested record has been received, but this is for the benefit of
+	 * future calls, to allow quick exit at the top of this function.
+	 */
+	if (readSource == XLOG_FROM_STREAM)
+	{
+		if (((*RecPtr) / XLOG_BLCKSZ) != (receivedUpto / XLOG_BLCKSZ))
+		{
+			readLen = XLOG_BLCKSZ;
+		}
+		else
+			readLen = receivedUpto % XLogSegSize - targetPageOff;
+	}
+	else
+		readLen = XLOG_BLCKSZ;
+
+	if (!readFileHeaderValidated && targetPageOff != 0)
+	{
+		/*
+		 * Whenever switching to a new WAL segment, we read the first page of
+		 * the file and validate its header, even if that's not where the
+		 * target record is.  This is so that we can check the additional
+		 * identification info that is present in the first page's "long"
+		 * header.
+		 */
+		readOff = 0;
+		if (read(readFile, readBuf, XLOG_BLCKSZ) != XLOG_BLCKSZ)
+		{
+			char fname[MAXFNAMELEN];
+			XLogFileName(fname, curFileTLI, readSegNo);
+			ereport(emode_for_corrupt_record(emode, *RecPtr),
+					(errcode_for_file_access(),
+					 errmsg("could not read from log segment %s, offset %u: %m",
+							fname, readOff)));
+			goto next_record_is_invalid;
+		}
+		if (!ValidXLogPageHeader((XLogPageHeader) readBuf, emode))
+			goto next_record_is_invalid;
+	}
+
+	/* Read the requested page */
+	readOff = targetPageOff;
+	if (lseek(readFile, (off_t) readOff, SEEK_SET) < 0)
+	{
+		char fname[MAXFNAMELEN];
+		XLogFileName(fname, curFileTLI, readSegNo);
+		ereport(emode_for_corrupt_record(emode, *RecPtr),
+				(errcode_for_file_access(),
+		 errmsg("could not seek in log segment %s to offset %u: %m",
+				fname, readOff)));
+		goto next_record_is_invalid;
+	}
+	if (read(readFile, readBuf, XLOG_BLCKSZ) != XLOG_BLCKSZ)
+	{
+		char fname[MAXFNAMELEN];
+		XLogFileName(fname, curFileTLI, readSegNo);
+		ereport(emode_for_corrupt_record(emode, *RecPtr),
+				(errcode_for_file_access(),
+		 errmsg("could not read from log segment %s, offset %u: %m",
+				fname, readOff)));
+		goto next_record_is_invalid;
+	}
+	if (!ValidXLogPageHeader((XLogPageHeader) readBuf, emode))
+		goto next_record_is_invalid;
+
+	readFileHeaderValidated = true;
+
+	Assert(targetSegNo == readSegNo);
+	Assert(targetPageOff == readOff);
+	Assert(targetRecOff < readLen);
+
+	return true;
+
+next_record_is_invalid:
+	failedSources |= readSource;
+
+	if (readFile >= 0)
+		close(readFile);
+	readFile = -1;
+	readLen = 0;
+	readSource = 0;
+
+	/* In standby-mode, keep trying */
+	if (StandbyMode)
+		goto retry;
+	else
+		return false;
+
+triggered:
+	if (readFile >= 0)
+		close(readFile);
+	readFile = -1;
+	readLen = 0;
+	readSource = 0;
+
+	return false;
+}
+
 /*
-			 * In standby mode, wait for the requested record to become
+ * In standby mode, wait for the requested record to become available, either
-			 * available, either via restore_command succeeding to restore the
+ * via restore_command succeeding to restore the segment, or via walreceiver
-			 * segment, or via walreceiver having streamed the record.
+ * having streamed the record (or via someone copying the segment directly to
+ * pg_xlog, but that is not documented or recommended).
+ *
+ * When the requested record becomes available, the function opens the file
+ * containing it (if not open already), and returns true. When end of standby
+ * mode is triggered by the user, and there is no more WAL available, returns
+ * false.
  */
+static bool
+WaitForWALToBecomeAvailable(XLogRecPtr RecPtr, bool randAccess,
+							bool fetching_ckpt)
+{
+	static pg_time_t last_fail_time = 0;
+
 	for (;;)
 	{
 		if (WalRcvInProgress())
@@ -9295,14 +9445,13 @@ retry:
 			bool		havedata;
 
 			/*
-					 * If we find an invalid record in the WAL streamed from
+			 * If we find an invalid record in the WAL streamed from master,
-					 * master, something is seriously wrong. There's little
+			 * something is seriously wrong. There's little chance that the
-					 * chance that the problem will just go away, but PANIC is
+			 * problem will just go away, but PANIC is not good for
-					 * not good for availability either, especially in hot
+			 * availability either, especially in hot standby mode.
-					 * standby mode. Disconnect, and retry from
+			 * Disconnect, and retry from archive/pg_xlog again. The WAL in
-					 * archive/pg_xlog again. The WAL in the archive should be
+			 * the archive should be identical to what was streamed, so it's
-					 * identical to what was streamed, so it's unlikely that
+			 * unlikely that it helps, but one can hope...
-					 * it helps, but one can hope...
 			 */
 			if (failedSources & XLOG_FROM_STREAM)
 			{
@@ -9313,26 +9462,25 @@ retry:
 			/*
 			 * Walreceiver is active, so see if new data has arrived.
 			 *
-					 * We only advance XLogReceiptTime when we obtain fresh
+			 * We only advance XLogReceiptTime when we obtain fresh WAL from
-					 * WAL from walreceiver and observe that we had already
+			 * walreceiver and observe that we had already processed
-					 * processed everything before the most recent "chunk"
+			 * everything before the most recent "chunk" that it flushed to
-					 * that it flushed to disk.  In steady state where we are
+			 * disk.  In steady state where we are keeping up with the
-					 * keeping up with the incoming data, XLogReceiptTime will
+			 * incoming data, XLogReceiptTime will be updated on each cycle.
-					 * be updated on each cycle.  When we are behind,
+			 * When we are behind, XLogReceiptTime will not advance, so the
-					 * XLogReceiptTime will not advance, so the grace time
+			 * grace time allotted to conflicting queries will decrease.
-					 * alloted to conflicting queries will decrease.
 			 */
-					if (XLByteLT(*RecPtr, receivedUpto))
+			if (XLByteLT(RecPtr, receivedUpto))
 				havedata = true;
 			else
 			{
 				XLogRecPtr	latestChunkStart;
 
 				receivedUpto = GetWalRcvWriteRecPtr(&latestChunkStart);
-						if (XLByteLT(*RecPtr, receivedUpto))
+				if (XLByteLT(RecPtr, receivedUpto))
 				{
 					havedata = true;
-							if (!XLByteLT(*RecPtr, latestChunkStart))
+					if (!XLByteLT(RecPtr, latestChunkStart))
 					{
 						XLogReceiptTime = GetCurrentTimestamp();
 						SetCurrentChunkStartTime(XLogReceiptTime);
@@ -9344,19 +9492,16 @@ retry:
 			if (havedata)
 			{
 				/*
-						 * Great, streamed far enough. Open the file if it's
+				 * Great, streamed far enough.  Open the file if it's not open
-						 * not open already.  Use XLOG_FROM_STREAM so that
+				 * already.  Use XLOG_FROM_STREAM so that source info is set
-						 * source info is set correctly and XLogReceiptTime
+				 * correctly and XLogReceiptTime isn't changed.
-						 * isn't changed.
 				 */
 				if (readFile < 0)
 				{
-							readFile =
+					readFile = XLogFileRead(readSegNo, PANIC,
-								XLogFileRead(readSegNo, PANIC,
+											curFileTLI,
-											 recoveryTargetTLI,
 											XLOG_FROM_STREAM, false);
 					Assert(readFile >= 0);
-							switched_segment = true;
 				}
 				else
 				{
@@ -9368,11 +9513,11 @@ retry:
 			}
 
 			/*
-					 * Data not here yet, so check for trigger then sleep for
+			 * Data not here yet, so check for trigger then sleep for five
-					 * five seconds like in the WAL file polling case below.
+			 * seconds like in the WAL file polling case below.
 			 */
 			if (CheckForStandbyTrigger())
-						goto retry;
+				return false;
 
 			/*
 			 * Wait for more WAL to arrive, or timeout to be reached
@@ -9384,13 +9529,12 @@ retry:
 		}
 		else
 		{
+			/*
+			 * WAL receiver is not active. Poll the archive.
+			 */
 			int			sources;
 			pg_time_t	now;
 
-					/*
-					 * Until walreceiver manages to reconnect, poll the
-					 * archive.
-					 */
 			if (readFile >= 0)
 			{
 				close(readFile);
@@ -9401,22 +9545,20 @@ retry:
 				curFileTLI = 0;
 
 			/*
-					 * Try to restore the file from archive, or read an
+			 * Try to restore the file from archive, or read an existing file
-					 * existing file from pg_xlog.
+			 * from pg_xlog.
 			 */
 			sources = XLOG_FROM_ARCHIVE | XLOG_FROM_PG_XLOG;
 			if (!(sources & ~failedSources))
 			{
 				/*
-						 * We've exhausted all options for retrieving the
+				 * We've exhausted all options for retrieving the file. Retry.
-						 * file. Retry.
 				 */
 				failedSources = 0;
 
 				/*
-						 * Before we sleep, re-scan for possible new timelines
+				 * Before we sleep, re-scan for possible new timelines if we
-						 * if we were requested to recover to the latest
+				 * were requested to recover to the latest timeline.
-						 * timeline.
 				 */
 				if (recoveryTargetIsLatest)
 				{
@@ -9425,8 +9567,8 @@ retry:
 				}
 
 				/*
-						 * If it hasn't been long since last attempt, sleep to
+				 * If it hasn't been long since last attempt, sleep to avoid
-						 * avoid busy-waiting.
+				 * busy-waiting.
 				 */
 				now = (pg_time_t) time(NULL);
 				if ((now - last_fail_time) < 5)
@@ -9437,30 +9579,27 @@ retry:
 				last_fail_time = now;
 
 				/*
-						 * If primary_conninfo is set, launch walreceiver to
+				 * If primary_conninfo is set, launch walreceiver to try to
-						 * try to stream the missing WAL, before retrying to
+				 * stream the missing WAL, before retrying to restore from
-						 * restore from archive/pg_xlog.
+				 * archive/pg_xlog.
 				 *
-						 * If fetching_ckpt is TRUE, RecPtr points to the
+				 * If fetching_ckpt is TRUE, RecPtr points to the initial
-						 * initial checkpoint location. In that case, we use
+				 * checkpoint location. In that case, we use RedoStartLSN as
-						 * RedoStartLSN as the streaming start position
+				 * the streaming start position instead of RecPtr, so that
-						 * instead of RecPtr, so that when we later jump
+				 * when we later jump backwards to start redo at RedoStartLSN,
-						 * backwards to start redo at RedoStartLSN, we will
+				 * we will have the logs streamed already.
-						 * have the logs streamed already.
 				 */
 				if (PrimaryConnInfo)
 				{
-							RequestXLogStreaming(
+					XLogRecPtr ptr = fetching_ckpt ? RedoStartLSN : RecPtr;
-									  fetching_ckpt ? RedoStartLSN : *RecPtr,
+
-												 PrimaryConnInfo);
+					RequestXLogStreaming(ptr, PrimaryConnInfo);
 					continue;
 				}
 			}
 			/* Don't try to read from a source that just failed */
 			sources &= ~failedSources;
-					readFile = XLogFileReadAnyTLI(readSegNo, DEBUG2,
+			readFile = XLogFileReadAnyTLI(readSegNo, DEBUG2, sources);
-												  sources);
-					switched_segment = true;
 			if (readFile >= 0)
 				break;
 
@@ -9470,147 +9609,23 @@ retry:
 			failedSources |= sources;
 
 			/*
-					 * Check to see if the trigger file exists. Note that we
+			 * Check to see if the trigger file exists. Note that we do this
-					 * do this only after failure, so when you create the
+			 * only after failure, so when you create the trigger file, we
-					 * trigger file, we still finish replaying as much as we
+			 * still finish replaying as much as we can from archive and
-					 * can from archive and pg_xlog before failover.
+			 * pg_xlog before failover.
 			 */
 			if (CheckForStandbyTrigger())
-						goto triggered;
-				}
-
-				/*
-				 * This possibly-long loop needs to handle interrupts of
-				 * startup process.
-				 */
-				HandleStartupProcInterrupts();
-			}
-		}
-		else
-		{
-			/* In archive or crash recovery. */
-			if (readFile < 0)
-			{
-				int			sources;
-
-				/* Reset curFileTLI if random fetch. */
-				if (randAccess)
-					curFileTLI = 0;
-
-				sources = XLOG_FROM_PG_XLOG;
-				if (InArchiveRecovery)
-					sources |= XLOG_FROM_ARCHIVE;
-
-				readFile = XLogFileReadAnyTLI(readSegNo, emode, sources);
-				switched_segment = true;
-				if (readFile < 0)
 				return false;
 		}
-		}
-	}
-
-	/*
-	 * At this point, we have the right segment open and if we're streaming we
-	 * know the requested record is in it.
-	 */
-	Assert(readFile != -1);
-
-	/*
-	 * If the current segment is being streamed from master, calculate how
-	 * much of the current page we have received already. We know the
-	 * requested record has been received, but this is for the benefit of
-	 * future calls, to allow quick exit at the top of this function.
-	 */
-	if (readSource == XLOG_FROM_STREAM)
-	{
-		if (((*RecPtr) / XLOG_BLCKSZ) != (receivedUpto / XLOG_BLCKSZ))
-		{
-			readLen = XLOG_BLCKSZ;
-		}
-		else
-			readLen = receivedUpto % XLogSegSize - targetPageOff;
-	}
-	else
-		readLen = XLOG_BLCKSZ;
 
-	if (switched_segment && targetPageOff != 0)
-	{
 		/*
-		 * Whenever switching to a new WAL segment, we read the first page of
+		 * This possibly-long loop needs to handle interrupts of startup
-		 * the file and validate its header, even if that's not where the
+		 * process.
-		 * target record is.  This is so that we can check the additional
-		 * identification info that is present in the first page's "long"
-		 * header.
 		 */
-		readOff = 0;
+		HandleStartupProcInterrupts();
-		if (read(readFile, readBuf, XLOG_BLCKSZ) != XLOG_BLCKSZ)
-		{
-			char fname[MAXFNAMELEN];
-			XLogFileName(fname, curFileTLI, readSegNo);
-			ereport(emode_for_corrupt_record(emode, *RecPtr),
-					(errcode_for_file_access(),
-					 errmsg("could not read from log segment %s, offset %u: %m",
-							fname, readOff)));
-			goto next_record_is_invalid;
-		}
-		if (!ValidXLogPageHeader((XLogPageHeader) readBuf, emode))
-			goto next_record_is_invalid;
-	}
-
-	/* Read the requested page */
-	readOff = targetPageOff;
-	if (lseek(readFile, (off_t) readOff, SEEK_SET) < 0)
-	{
-		char fname[MAXFNAMELEN];
-		XLogFileName(fname, curFileTLI, readSegNo);
-		ereport(emode_for_corrupt_record(emode, *RecPtr),
-				(errcode_for_file_access(),
-		 errmsg("could not seek in log segment %s to offset %u: %m",
-				fname, readOff)));
-		goto next_record_is_invalid;
-	}
-	if (read(readFile, readBuf, XLOG_BLCKSZ) != XLOG_BLCKSZ)
-	{
-		char fname[MAXFNAMELEN];
-		XLogFileName(fname, curFileTLI, readSegNo);
-		ereport(emode_for_corrupt_record(emode, *RecPtr),
-				(errcode_for_file_access(),
-		 errmsg("could not read from log segment %s, offset %u: %m",
-				fname, readOff)));
-		goto next_record_is_invalid;
 	}
-	if (!ValidXLogPageHeader((XLogPageHeader) readBuf, emode))
-		goto next_record_is_invalid;
-
-	Assert(targetSegNo == readSegNo);
-	Assert(targetPageOff == readOff);
-	Assert(targetRecOff < readLen);
 
 	return true;
-
-next_record_is_invalid:
-	failedSources |= readSource;
-
-	if (readFile >= 0)
-		close(readFile);
-	readFile = -1;
-	readLen = 0;
-	readSource = 0;
-
-	/* In standby-mode, keep trying */
-	if (StandbyMode)
-		goto retry;
-	else
-		return false;
-
-triggered:
-	if (readFile >= 0)
-		close(readFile);
-	readFile = -1;
-	readLen = 0;
-	readSource = 0;
-
-	return false;
 }
 
 /*