Make WAL segment size configurable at initdb time.

For performance reasons a larger segment size than the default 16MB
can be useful. A larger segment size has two main benefits: Firstly,
in setups using archiving, it makes it easier to write scripts that
can keep up with higher amounts of WAL, secondly, the WAL has to be
written and synced to disk less frequently.

But at the same time large segment size are disadvantageous for
smaller databases. So far the segment size had to be configured at
compile time, often making it unrealistic to choose one fitting to a
particularly load. Therefore change it to a initdb time setting.

This includes a breaking changes to the xlogreader.h API, which now
requires the current segment size to be configured.  For that and
similar reasons a number of binaries had to be taught how to recognize
the current segment size.

Author: Beena Emerson, editorialized by Andres Freund
Reviewed-By: Andres Freund, David Steele, Kuntal Ghosh, Michael
    Paquier, Peter Eisentraut, Robert Hass, Tushar Ahuja
Discussion: https://postgr.es/m/CAOG9ApEAcQ--1ieKbhFzXSQPw_YLmepaa4hNdnY5+ZULpt81Mw@mail.gmail.com

1 files changed, 19 insertions, 17 deletions

diff --git a/src/bin/pg_basebackup/receivelog.c b/src/bin/pg_basebackup/receivelog.c
index 888458f4a90..65931f64541 100644
--- a/src/bin/pg_basebackup/receivelog.c
+++ b/src/bin/pg_basebackup/receivelog.c
@@ -95,17 +95,17 @@ open_walfile(StreamCtl *stream, XLogRecPtr startpoint)
 	ssize_t		size;
 	XLogSegNo	segno;
 
-	XLByteToSeg(startpoint, segno);
-	XLogFileName(current_walfile_name, stream->timeline, segno);
+	XLByteToSeg(startpoint, segno, WalSegSz);
+	XLogFileName(current_walfile_name, stream->timeline, segno, WalSegSz);
 
 	snprintf(fn, sizeof(fn), "%s%s", current_walfile_name,
 			 stream->partial_suffix ? stream->partial_suffix : "");
 
 	/*
 	 * When streaming to files, if an existing file exists we verify that it's
-	 * either empty (just created), or a complete XLogSegSize segment (in
-	 * which case it has been created and padded). Anything else indicates a
-	 * corrupt file.
+	 * either empty (just created), or a complete WalSegSz segment (in which
+	 * case it has been created and padded). Anything else indicates a corrupt
+	 * file.
 	 *
 	 * When streaming to tar, no file with this name will exist before, so we
 	 * never have to verify a size.
@@ -120,7 +120,7 @@ open_walfile(StreamCtl *stream, XLogRecPtr startpoint)
 					progname, fn, stream->walmethod->getlasterror());
 			return false;
 		}
-		if (size == XLogSegSize)
+		if (size == WalSegSz)
 		{
 			/* Already padded file. Open it for use */
 			f = stream->walmethod->open_for_write(current_walfile_name, stream->partial_suffix, 0);
@@ -154,7 +154,7 @@ open_walfile(StreamCtl *stream, XLogRecPtr startpoint)
 					ngettext("%s: write-ahead log file \"%s\" has %d byte, should be 0 or %d\n",
 							 "%s: write-ahead log file \"%s\" has %d bytes, should be 0 or %d\n",
 							 size),
-					progname, fn, (int) size, XLogSegSize);
+					progname, fn, (int) size, WalSegSz);
 			return false;
 		}
 		/* File existed and was empty, so fall through and open */
@@ -162,7 +162,8 @@ open_walfile(StreamCtl *stream, XLogRecPtr startpoint)
 
 	/* No file existed, so create one */
 
-	f = stream->walmethod->open_for_write(current_walfile_name, stream->partial_suffix, XLogSegSize);
+	f = stream->walmethod->open_for_write(current_walfile_name,
+										  stream->partial_suffix, WalSegSz);
 	if (f == NULL)
 	{
 		fprintf(stderr,
@@ -203,7 +204,7 @@ close_walfile(StreamCtl *stream, XLogRecPtr pos)
 
 	if (stream->partial_suffix)
 	{
-		if (currpos == XLOG_SEG_SIZE)
+		if (currpos == WalSegSz)
 			r = stream->walmethod->close(walfile, CLOSE_NORMAL);
 		else
 		{
@@ -231,7 +232,7 @@ close_walfile(StreamCtl *stream, XLogRecPtr pos)
 	 * new node. This is in line with walreceiver.c always doing a
 	 * XLogArchiveForceDone() after a complete segment.
 	 */
-	if (currpos == XLOG_SEG_SIZE && stream->mark_done)
+	if (currpos == WalSegSz && stream->mark_done)
 	{
 		/* writes error message if failed */
 		if (!mark_file_as_archived(stream, current_walfile_name))
@@ -676,7 +677,8 @@ ReceiveXlogStream(PGconn *conn, StreamCtl *stream)
 			 * start streaming at the beginning of a segment.
 			 */
 			stream->timeline = newtimeline;
-			stream->startpos = stream->startpos - (stream->startpos % XLOG_SEG_SIZE);
+			stream->startpos = stream->startpos -
+				XLogSegmentOffset(stream->startpos, WalSegSz);
 			continue;
 		}
 		else if (PQresultStatus(res) == PGRES_COMMAND_OK)
@@ -1111,7 +1113,7 @@ ProcessXLogDataMsg(PGconn *conn, StreamCtl *stream, char *copybuf, int len,
 	*blockpos = fe_recvint64(&copybuf[1]);
 
 	/* Extract WAL location for this block */
-	xlogoff = *blockpos % XLOG_SEG_SIZE;
+	xlogoff = XLogSegmentOffset(*blockpos, WalSegSz);
 
 	/*
 	 * Verify that the initial location in the stream matches where we think
@@ -1148,11 +1150,11 @@ ProcessXLogDataMsg(PGconn *conn, StreamCtl *stream, char *copybuf, int len,
 		int			bytes_to_write;
 
 		/*
-		 * If crossing a WAL boundary, only write up until we reach
-		 * XLOG_SEG_SIZE.
+		 * If crossing a WAL boundary, only write up until we reach wal
+		 * segment size.
 		 */
-		if (xlogoff + bytes_left > XLOG_SEG_SIZE)
-			bytes_to_write = XLOG_SEG_SIZE - xlogoff;
+		if (xlogoff + bytes_left > WalSegSz)
+			bytes_to_write = WalSegSz - xlogoff;
 		else
 			bytes_to_write = bytes_left;
 
@@ -1182,7 +1184,7 @@ ProcessXLogDataMsg(PGconn *conn, StreamCtl *stream, char *copybuf, int len,
 		xlogoff += bytes_to_write;
 
 		/* Did we reach the end of a WAL segment? */
-		if (*blockpos % XLOG_SEG_SIZE == 0)
+		if (XLogSegmentOffset(*blockpos, WalSegSz) == 0)
 		{
 			if (!close_walfile(stream, *blockpos))
 				/* Error message written in close_walfile() */