From 7af716134dceb3bafce421dfeaffebf1e1e3e17d Mon Sep 17 00:00:00 2001
From: Kyotaro Horiguchi <horikyoga.ntt@gmail.com>
Date: Mon, 29 Jun 2020 16:12:01 +0900
Subject: [PATCH v1] Make sure standby archives all segments immediately

Standby may get a bit being late in archive, since walsender doesn't
archive a segment until it receives any data for the next segment, Fix
that by archiving just after a segment is finished.

Also, standby fails to archive a segment if standby is stopped just
after a segment is finished or stopped just after a segment
swtich. Make sure that walreceiver archives all segments by rechecking
at start.
---
 src/backend/replication/walreceiver.c | 82 ++++++++++++++++++---------
 1 file changed, 54 insertions(+), 28 deletions(-)

diff --git a/src/backend/replication/walreceiver.c b/src/backend/replication/walreceiver.c
index d1ad75da87..831718c859 100644
--- a/src/backend/replication/walreceiver.c
+++ b/src/backend/replication/walreceiver.c
@@ -902,49 +902,34 @@ XLogWalRcvWrite(char *buf, Size nbytes, XLogRecPtr recptr)
 	{
 		int			segbytes;
 
-		if (recvFile < 0 || !XLByteInSeg(recptr, recvSegNo, wal_segment_size))
+		/* Open the segment if not yet */
+		if (recvFile < 0)
 		{
 			bool		use_existent;
 
+			recvFileTLI = ThisTimeLineID;
+
 			/*
-			 * fsync() and close current file before we switch to next one. We
-			 * would otherwise have to reopen this file to fsync it later
+			 * If we are starting streaming at the beginning of a segment,
+			 * there may be the case where the previous segment have not been
+			 * archived yet.  Make sure it is archived.
 			 */
-			if (recvFile >= 0)
+			if (XLogArchiveMode == ARCHIVE_MODE_ALWAYS && recvSegNo == 0)
 			{
 				char		xlogfname[MAXFNAMELEN];
+				XLogSegNo	prevseg;
 
-				XLogWalRcvFlush(false);
+				XLByteToPrevSeg(recptr, prevseg, wal_segment_size);
+				XLogFileName(xlogfname, recvFileTLI, prevseg, wal_segment_size);
 
-				XLogFileName(xlogfname, recvFileTLI, recvSegNo, wal_segment_size);
-
-				/*
-				 * XLOG segment files will be re-read by recovery in startup
-				 * process soon, so we don't advise the OS to release cache
-				 * pages associated with the file like XLogFileClose() does.
-				 */
-				if (close(recvFile) != 0)
-					ereport(PANIC,
-							(errcode_for_file_access(),
-							 errmsg("could not close log segment %s: %m",
-									xlogfname)));
-
-				/*
-				 * Create .done file forcibly to prevent the streamed segment
-				 * from being archived later.
-				 */
-				if (XLogArchiveMode != ARCHIVE_MODE_ALWAYS)
-					XLogArchiveForceDone(xlogfname);
-				else
-					XLogArchiveNotify(xlogfname);
+				/* Mark as ".ready" of not yet */
+				XLogArchiveCheckDone(xlogfname);
 			}
-			recvFile = -1;
 
 			/* Create/use new log file */
 			XLByteToSeg(recptr, recvSegNo, wal_segment_size);
 			use_existent = true;
 			recvFile = XLogFileInit(recvSegNo, &use_existent, true);
-			recvFileTLI = ThisTimeLineID;
 		}
 
 		/* Calculate the start offset of the received logs */
@@ -985,6 +970,47 @@ XLogWalRcvWrite(char *buf, Size nbytes, XLogRecPtr recptr)
 		buf += byteswritten;
 
 		LogstreamResult.Write = recptr;
+
+		/*
+		 * Close the current WAL segment if it is completed then let the file
+		 * be archived if needed.
+		 */
+		if (!XLByteInSeg(recptr, recvSegNo, wal_segment_size))
+		{
+			char		xlogfname[MAXFNAMELEN];
+
+			Assert (recvFile >= 0);
+
+			/*
+			 * fsync() and close current file before we switch to next one. We
+			 * would otherwise have to reopen this file to fsync it later
+			 */
+			XLogWalRcvFlush(false);
+
+			XLogFileName(xlogfname, recvFileTLI, recvSegNo, wal_segment_size);
+
+			/*
+			 * XLOG segment files will be re-read by recovery in startup
+			 * process soon, so we don't advise the OS to release cache
+			 * pages associated with the file like XLogFileClose() does.
+			 */
+			if (close(recvFile) != 0)
+				ereport(PANIC,
+						(errcode_for_file_access(),
+						 errmsg("could not close log segment %s: %m",
+								xlogfname)));
+
+			/*
+			 * Create .done file forcibly to prevent the streamed segment
+			 * from being archived later.
+			 */
+			if (XLogArchiveMode != ARCHIVE_MODE_ALWAYS)
+				XLogArchiveForceDone(xlogfname);
+			else
+				XLogArchiveNotify(xlogfname);
+
+			recvFile = -1;
+		}
 	}
 
 	/* Update shared-memory status */
-- 
2.18.4