Prevent WAL files created by pg_basebackup -x/X from being archived again.

WAL (and timeline history) files created by pg_basebackup did not
maintain the new base backup's archive status. That's currently not a
problem if the new node is used as a standby - but if that node is
promoted all still existing files can get archived again.  With a high
wal_keep_segment settings that can happen a significant time later -
which is quite confusing.

Change both the backend (for the -x/-X fetch case) and pg_basebackup
(for -X stream) itself to always mark WAL/timeline files included in
the base backup as .done. That's in line with walreceiver.c doing so.

The verbosity of the pg_basebackup changes show pretty clearly that it
needs some refactoring, but that'd result in not be backpatchable
changes.

Backpatch to 9.1 where pg_basebackup was introduced.

Discussion: 20141205002854.GE21964@awork2.anarazel.de

src/backend/replication/basebackup.c

@@ -400,6 +400,7 @@ perform_base_backup(basebackup_options *opt, DIR *tblspcdir)
 						 errmsg("unexpected WAL file size \"%s\"", walFiles[i])));
 			}
 
+			/* send the WAL file itself */
 			_tarWriteHeader(pathbuf, NULL, &statbuf);
 
 			while ((cnt = fread(buf, 1, Min(sizeof(buf), XLogSegSize - len), fp)) > 0)
@@ -424,7 +425,17 @@ perform_base_backup(basebackup_options *opt, DIR *tblspcdir)
 			}
 
 			/* XLogSegSize is a multiple of 512, so no need for padding */
+
 			FreeFile(fp);
+
+			/*
+			 * Mark file as archived, otherwise files can get archived again
+			 * after promotion of a new node. This is in line with
+			 * walreceiver.c always doing a XLogArchiveForceDone() after a
+			 * complete segment.
+			 */
+			StatusFilePath(pathbuf, walFiles[i], ".done");
+			sendFileWithContent(pathbuf, "");
 		}
 
 		/*
@@ -447,6 +458,10 @@ perform_base_backup(basebackup_options *opt, DIR *tblspcdir)
 						 errmsg("could not stat file \"%s\": %m", pathbuf)));
 
 			sendFile(pathbuf, pathbuf, &statbuf, false);
+
+			/* unconditionally mark file as archived */
+			StatusFilePath(pathbuf, fname, ".done");
+			sendFileWithContent(pathbuf, "");
 		}
 
 		/* Send CopyDone message for the last tar file */
@@ -881,6 +896,15 @@ sendDir(char *path, int basepathlen, bool sizeonly, List *tablespaces)
 				_tarWriteHeader(pathbuf + basepathlen + 1, NULL, &statbuf);
 			}
 			size += 512;		/* Size of the header just added */
+
+			/*
+			 * Also send archive_status directory (by hackishly reusing
+			 * statbuf from above ...).
+			 */
+			if (!sizeonly)
+				_tarWriteHeader("./pg_xlog/archive_status", NULL, &statbuf);
+			size += 512;		/* Size of the header just added */
+
 			continue;			/* don't recurse into pg_xlog */
 		}
 

src/bin/pg_basebackup/pg_basebackup.c

@@ -259,7 +259,7 @@ LogStreamerMain(logstreamer_param *param)
 	if (!ReceiveXlogStream(param->bgconn, param->startptr, param->timeline,
 						   param->sysidentifier, param->xlogdir,
 						   reached_end_position, standby_message_timeout,
-						   true))
+						   true, true))
 
 		/*
 		 * Any errors will already have been reported in the function process,
@@ -281,6 +281,7 @@ static void
 StartLogStreamer(char *startpos, uint32 timeline, char *sysidentifier)
 {
 	logstreamer_param *param;
+	char		statusdir[MAXPGPATH];
 
 	param = xmalloc0(sizeof(logstreamer_param));
 	param->timeline = timeline;
@@ -314,13 +315,23 @@ StartLogStreamer(char *startpos, uint32 timeline, char *sysidentifier)
 		/* Error message already written in GetConnection() */
 		exit(1);
 
-	/*
-	 * Always in plain format, so we can write to basedir/pg_xlog. But the
-	 * directory entry in the tar file may arrive later, so make sure it's
-	 * created before we start.
-	 */
 	snprintf(param->xlogdir, sizeof(param->xlogdir), "%s/pg_xlog", basedir);
-	verify_dir_is_empty_or_create(param->xlogdir);
+
+	/*
+	 * Create pg_xlog/archive_status (and thus pg_xlog) so we can can write to
+	 * basedir/pg_xlog as the directory entry in the tar file may arrive
+	 * later.
+	 */
+	snprintf(statusdir, sizeof(statusdir), "%s/pg_xlog/archive_status",
+			 basedir);
+
+	if (pg_mkdir_p(statusdir, S_IRWXU) != 0 && errno != EEXIST)
+	{
+		fprintf(stderr,
+				_("%s: could not create directory \"%s\": %s\n"),
+				progname, statusdir, strerror(errno));
+		disconnect_and_exit(1);
+	}
 
 	/*
 	 * Start a child process and tell it to start streaming. On Unix, this is
@@ -403,6 +414,23 @@ verify_dir_is_empty_or_create(char *dirname)
 	}
 }
 
+/*
+ * Returns whether the string `str' has the postfix `end'.
+ */
+static bool
+pg_str_endswith(const char *str, const char *end)
+{
+	size_t		slen = strlen(str);
+	size_t		elen = strlen(end);
+
+	/* can't be a postfix if longer */
+	if (elen > slen)
+		return false;
+
+	/* compare the end of the strings */
+	str += slen - elen;
+	return strcmp(str, end) == 0;
+}
 
 /*
  * Print a progress report based on the global variables. If verbose output
@@ -835,10 +863,12 @@ ReceiveAndUnpackTarFile(PGconn *conn, PGresult *res, int rownum)
 					{
 						/*
 						 * When streaming WAL, pg_xlog will have been created
-						 * by the wal receiver process, so just ignore failure
-						 * on that.
+						 * by the wal receiver process. So just ignore creation
+						 * failures on related directories.
 						 */
-						if (!streamwal || strcmp(filename + strlen(filename) - 8, "/pg_xlog") != 0)
+						if (!((pg_str_endswith(filename, "/pg_xlog") ||
+							   pg_str_endswith(filename, "/archive_status")) &&
+							  errno == EEXIST))
 						{
 							fprintf(stderr,
 							_("%s: could not create directory \"%s\": %s\n"),

src/bin/pg_basebackup/pg_receivexlog.c

@@ -321,7 +321,7 @@ StreamLog(void)
 				progname, startpos.xlogid, startpos.xrecoff, timeline);
 
 	ReceiveXlogStream(conn, startpos, timeline, NULL, basedir,
-					  stop_streaming, standby_message_timeout, false);
+					  stop_streaming, standby_message_timeout, false, true);
 
 	PQfinish(conn);
 }

src/bin/pg_basebackup/receivelog.c

@@ -44,6 +44,35 @@ const XLogRecPtr InvalidXLogRecPtr = {0, 0};
 static int	walfile = -1;
 
 
+static bool
+mark_file_as_archived(const char *basedir, const char *fname)
+{
+	int fd;
+	static char tmppath[MAXPGPATH];
+
+	snprintf(tmppath, sizeof(tmppath), "%s/archive_status/%s.done",
+			 basedir, fname);
+
+	fd = open(tmppath, O_WRONLY | O_CREAT | PG_BINARY, S_IRUSR | S_IWUSR);
+	if (fd < 0)
+	{
+		fprintf(stderr, _("%s: could not create archive status file \"%s\": %s\n"),
+				progname, tmppath, strerror(errno));
+		return false;
+	}
+
+	if (fsync(fd) != 0)
+	{
+		fprintf(stderr, _("%s: could not fsync file \"%s\": %s\n"),
+				progname, tmppath, strerror(errno));
+		return false;
+	}
+
+	close(fd);
+
+	return true;
+}
+
 /*
  * Open a new WAL file in the specified directory. Store the name
  * (not including the full directory) in namebuf. Assumes there is
@@ -133,7 +162,8 @@ open_walfile(XLogRecPtr startpoint, uint32 timeline, char *basedir,
  * completed writing the whole segment.
  */
 static bool
-close_walfile(char *basedir, char *walname, bool segment_complete)
+close_walfile(char *basedir, char *walname, bool segment_complete,
+			  bool mark_done)
 {
 	off_t		currpos = lseek(walfile, 0, SEEK_CUR);
 
@@ -184,6 +214,19 @@ close_walfile(char *basedir, char *walname, bool segment_complete)
 				_("%s: not renaming \"%s\", segment is not complete\n"),
 				progname, walname);
 
+	/*
+	 * Mark file as archived if requested by the caller - pg_basebackup needs
+	 * to do so as files can otherwise get archived again after promotion of a
+	 * new node. This is in line with walreceiver.c always doing a
+	 * XLogArchiveForceDone() after a complete segment.
+	 */
+	if (currpos == XLOG_SEG_SIZE && mark_done)
+	{
+		/* writes error message if failed */
+		if (!mark_file_as_archived(basedir, walname))
+			return false;
+	}
+
 	return true;
 }
 
@@ -284,7 +327,8 @@ bool
 ReceiveXlogStream(PGconn *conn, XLogRecPtr startpos, uint32 timeline,
 				  char *sysidentifier, char *basedir,
 				  stream_stop_callback stream_stop,
-				  int standby_message_timeout, bool rename_partial)
+				  int standby_message_timeout, bool rename_partial,
+				  bool mark_done)
 {
 	char		query[128];
 	char		current_walfile_name[MAXPGPATH];
@@ -343,7 +387,6 @@ ReceiveXlogStream(PGconn *conn, XLogRecPtr startpos, uint32 timeline,
 		return false;
 	}
 	PQclear(res);
-
 	/*
 	 * Receive the actual xlog data
 	 */
@@ -367,7 +410,7 @@ ReceiveXlogStream(PGconn *conn, XLogRecPtr startpos, uint32 timeline,
 		if (stream_stop && stream_stop(blockpos, timeline, false))
 		{
 			if (walfile != -1 && !close_walfile(basedir, current_walfile_name,
-												rename_partial))
+												rename_partial, mark_done))
 				/* Potential error message is written by close_walfile */
 				goto error;
 			return true;
@@ -579,7 +622,8 @@ ReceiveXlogStream(PGconn *conn, XLogRecPtr startpos, uint32 timeline,
 			/* Did we reach the end of a WAL segment? */
 			if (blockpos.xrecoff % XLOG_SEG_SIZE == 0)
 			{
-				if (!close_walfile(basedir, current_walfile_name, false))
+				if (!close_walfile(basedir, current_walfile_name, false,
+								   mark_done))
 					/* Error message written in close_walfile() */
 					goto error;
 

src/bin/pg_basebackup/receivelog.h

@@ -13,4 +13,5 @@ extern bool ReceiveXlogStream(PGconn *conn,
 				  char *basedir,
 				  stream_stop_callback stream_stop,
 				  int standby_message_timeout,
-				  bool rename_partial);
+				  bool rename_partial,
+				  bool mark_done);