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, 15 deletions

diff --git a/src/backend/replication/basebackup.c b/src/backend/replication/basebackup.c
index 12a16bd773d..c3b9bddc8fe 100644
--- a/src/backend/replication/basebackup.c
+++ b/src/backend/replication/basebackup.c
@@ -357,10 +357,10 @@ perform_base_backup(basebackup_options *opt, DIR *tblspcdir)
 		 * shouldn't be such files, but if there are, there's little harm in
 		 * including them.
 		 */
-		XLByteToSeg(startptr, startsegno);
-		XLogFileName(firstoff, ThisTimeLineID, startsegno);
-		XLByteToPrevSeg(endptr, endsegno);
-		XLogFileName(lastoff, ThisTimeLineID, endsegno);
+		XLByteToSeg(startptr, startsegno, wal_segment_size);
+		XLogFileName(firstoff, ThisTimeLineID, startsegno, wal_segment_size);
+		XLByteToPrevSeg(endptr, endsegno, wal_segment_size);
+		XLogFileName(lastoff, ThisTimeLineID, endsegno, wal_segment_size);
 
 		dir = AllocateDir("pg_wal");
 		if (!dir)
@@ -415,12 +415,13 @@ perform_base_backup(basebackup_options *opt, DIR *tblspcdir)
 		 * Sanity check: the first and last segment should cover startptr and
 		 * endptr, with no gaps in between.
 		 */
-		XLogFromFileName(walFiles[0], &tli, &segno);
+		XLogFromFileName(walFiles[0], &tli, &segno, wal_segment_size);
 		if (segno != startsegno)
 		{
 			char		startfname[MAXFNAMELEN];
 
-			XLogFileName(startfname, ThisTimeLineID, startsegno);
+			XLogFileName(startfname, ThisTimeLineID, startsegno,
+						 wal_segment_size);
 			ereport(ERROR,
 					(errmsg("could not find WAL file \"%s\"", startfname)));
 		}
@@ -429,12 +430,13 @@ perform_base_backup(basebackup_options *opt, DIR *tblspcdir)
 			XLogSegNo	currsegno = segno;
 			XLogSegNo	nextsegno = segno + 1;
 
-			XLogFromFileName(walFiles[i], &tli, &segno);
+			XLogFromFileName(walFiles[i], &tli, &segno, wal_segment_size);
 			if (!(nextsegno == segno || currsegno == segno))
 			{
 				char		nextfname[MAXFNAMELEN];
 
-				XLogFileName(nextfname, ThisTimeLineID, nextsegno);
+				XLogFileName(nextfname, ThisTimeLineID, nextsegno,
+							 wal_segment_size);
 				ereport(ERROR,
 						(errmsg("could not find WAL file \"%s\"", nextfname)));
 			}
@@ -443,7 +445,7 @@ perform_base_backup(basebackup_options *opt, DIR *tblspcdir)
 		{
 			char		endfname[MAXFNAMELEN];
 
-			XLogFileName(endfname, ThisTimeLineID, endsegno);
+			XLogFileName(endfname, ThisTimeLineID, endsegno, wal_segment_size);
 			ereport(ERROR,
 					(errmsg("could not find WAL file \"%s\"", endfname)));
 		}
@@ -457,7 +459,7 @@ perform_base_backup(basebackup_options *opt, DIR *tblspcdir)
 			pgoff_t		len = 0;
 
 			snprintf(pathbuf, MAXPGPATH, XLOGDIR "/%s", walFiles[i]);
-			XLogFromFileName(walFiles[i], &tli, &segno);
+			XLogFromFileName(walFiles[i], &tli, &segno, wal_segment_size);
 
 			fp = AllocateFile(pathbuf, "rb");
 			if (fp == NULL)
@@ -479,7 +481,7 @@ perform_base_backup(basebackup_options *opt, DIR *tblspcdir)
 						(errcode_for_file_access(),
 						 errmsg("could not stat file \"%s\": %m",
 								pathbuf)));
-			if (statbuf.st_size != XLogSegSize)
+			if (statbuf.st_size != wal_segment_size)
 			{
 				CheckXLogRemoved(segno, tli);
 				ereport(ERROR,
@@ -490,7 +492,9 @@ perform_base_backup(basebackup_options *opt, DIR *tblspcdir)
 			/* send the WAL file itself */
 			_tarWriteHeader(pathbuf, NULL, &statbuf, false);
 
-			while ((cnt = fread(buf, 1, Min(sizeof(buf), XLogSegSize - len), fp)) > 0)
+			while ((cnt = fread(buf, 1,
+								Min(sizeof(buf), wal_segment_size - len),
+								fp)) > 0)
 			{
 				CheckXLogRemoved(segno, tli);
 				/* Send the chunk as a CopyData message */
@@ -501,11 +505,11 @@ perform_base_backup(basebackup_options *opt, DIR *tblspcdir)
 				len += cnt;
 				throttle(cnt);
 
-				if (len == XLogSegSize)
+				if (len == wal_segment_size)
 					break;
 			}
 
-			if (len != XLogSegSize)
+			if (len != wal_segment_size)
 			{
 				CheckXLogRemoved(segno, tli);
 				ereport(ERROR,
@@ -513,7 +517,7 @@ perform_base_backup(basebackup_options *opt, DIR *tblspcdir)
 						 errmsg("unexpected WAL file size \"%s\"", walFiles[i])));
 			}
 
-			/* XLogSegSize is a multiple of 512, so no need for padding */
+			/* wal_segment_size is a multiple of 512, so no need for padding */
 
 			FreeFile(fp);