Arrange to recycle old XLOG log segment files as new segment files,

rather than deleting them only to have to create more.  Steady state
is 2*CHECKPOINT_SEGMENTS + WAL_FILES + 1 segment files, which will
simply be renamed rather than constantly deleted and recreated.
To make this safe, added current XLOG file/offset number to page
header of XLOG pages, so that an un-overwritten page from an old
incarnation of a logfile can be reliably told from a valid page.
This change means that if you try to restart postmaster in a CVS-tip
database after installing the change, you'll get a complaint about
bad XLOG page magic number.  If you don't want to initdb, run
contrib/pg_resetxlog (and be sure you shut down the old postmaster
cleanly).

contrib/pg_resetxlog/pg_resetxlog.c

@@ -23,7 +23,7 @@
  * Portions Copyright (c) 1996-2001, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $Header: /cvsroot/pgsql/contrib/pg_resetxlog/Attic/pg_resetxlog.c,v 1.5 2001/06/06 17:07:38 tgl Exp $
+ * $Header: /cvsroot/pgsql/contrib/pg_resetxlog/Attic/pg_resetxlog.c,v 1.6 2001/07/19 02:12:34 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -857,6 +857,10 @@ WriteEmptyXLOG(void)
 	page->xlp_magic = XLOG_PAGE_MAGIC;
 	page->xlp_info = 0;
 	page->xlp_sui = ControlFile.checkPointCopy.ThisStartUpID;
+	page->xlp_pageaddr.xlogid =
+		ControlFile.checkPointCopy.redo.xlogid;
+	page->xlp_pageaddr.xrecoff =
+		ControlFile.checkPointCopy.redo.xrecoff - SizeOfXLogPHD;
 	record = (XLogRecord *) ((char *) page + SizeOfXLogPHD);
 	record->xl_prev.xlogid = 0;
 	record->xl_prev.xrecoff = 0;

src/include/access/xlog.h

@@ -6,7 +6,7 @@
  * Portions Copyright (c) 1996-2001, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $Id: xlog.h,v 1.23 2001/03/22 04:00:32 momjian Exp $
+ * $Id: xlog.h,v 1.24 2001/07/19 02:12:35 tgl Exp $
  */
 #ifndef XLOG_H
 #define XLOG_H
@@ -109,13 +109,14 @@ typedef struct XLogContRecord
 /*
  * Each page of XLOG file has a header like this:
  */
-#define XLOG_PAGE_MAGIC 0xD058	/* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD059	/* can be used as WAL version indicator */
 
 typedef struct XLogPageHeaderData
 {
 	uint16		xlp_magic;		/* magic value for correctness checks */
 	uint16		xlp_info;		/* flag bits, see below */
 	StartUpID	xlp_sui;		/* StartUpID of first record on page */
+	XLogRecPtr	xlp_pageaddr;	/* XLOG address of this page */
 } XLogPageHeaderData;
 
 #define SizeOfXLogPHD	MAXALIGN(sizeof(XLogPageHeaderData))