Remove the logId/logSeg fields from pg_control, because they are not needed

in normal operation, and we can avoid rewriting pg_control at every log
segment switch if we don't insist that these values be valid.  Reducing
the number of pg_control updates is a good idea for both performance and
reliability.  It does make pg_resetxlog's life a bit harder, but that seems
a good tradeoff; and anyway the change to pg_resetxlog amounts to automating
something people formerly needed to do by hand, namely look at the existing
pg_xlog files to make sure the new WAL start point was past them.

In passing, change the wording of xlog.c's "database system was interrupted"
messages: describe the pg_control timestamp as "last known up at" rather than
implying it is the exact time of service interruption.  With this change the
timestamp will generally be the time of the last checkpoint, which could be
many minutes before the failure; and we've already seen indications that
people tend to misinterpret the old wording.

initdb forced due to change in pg_control layout.  Simon Riggs and Tom Lane

2 files changed, 113 insertions, 34 deletions

diff --git a/src/bin/pg_controldata/pg_controldata.c b/src/bin/pg_controldata/pg_controldata.c
index cbde5357ed..6805af6153 100644
--- a/src/bin/pg_controldata/pg_controldata.c
+++ b/src/bin/pg_controldata/pg_controldata.c
@@ -6,7 +6,7 @@
  * copyright (c) Oliver Elphick <olly@lfix.co.uk>, 2001;
  * licence: BSD
  *
- * $PostgreSQL: pgsql/src/bin/pg_controldata/pg_controldata.c,v 1.31 2006/08/21 16:16:31 tgl Exp $
+ * $PostgreSQL: pgsql/src/bin/pg_controldata/pg_controldata.c,v 1.32 2006/12/08 19:50:53 tgl Exp $
  */
 #include "postgres.h"
 
@@ -159,10 +159,6 @@ main(int argc, char *argv[])
 		   dbState(ControlFile.state));
 	printf(_("pg_control last modified:             %s\n"),
 		   pgctime_str);
-	printf(_("Current log file ID:                  %u\n"),
-		   ControlFile.logId);
-	printf(_("Next log file segment:                %u\n"),
-		   ControlFile.logSeg);
 	printf(_("Latest checkpoint location:           %X/%X\n"),
 		   ControlFile.checkPoint.xlogid,
 		   ControlFile.checkPoint.xrecoff);
diff --git a/src/bin/pg_resetxlog/pg_resetxlog.c b/src/bin/pg_resetxlog/pg_resetxlog.c
index 1561383279..9212ccc5b7 100644
--- a/src/bin/pg_resetxlog/pg_resetxlog.c
+++ b/src/bin/pg_resetxlog/pg_resetxlog.c
@@ -23,7 +23,7 @@
  * Portions Copyright (c) 1996-2006, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/bin/pg_resetxlog/pg_resetxlog.c,v 1.53 2006/10/04 00:30:05 momjian Exp $
+ * $PostgreSQL: pgsql/src/bin/pg_resetxlog/pg_resetxlog.c,v 1.54 2006/12/08 19:50:53 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -60,6 +60,7 @@ static bool ReadControlFile(void);
 static void GuessControlValues(void);
 static void PrintControlValues(bool guessed);
 static void RewriteControlFile(void);
+static void FindEndOfXLOG(void);
 static void KillExistingXLOG(void);
 static void WriteEmptyXLOG(void);
 static void usage(void);
@@ -284,6 +285,11 @@ main(int argc, char *argv[])
 		GuessControlValues();
 
 	/*
+	 * Also look at existing segment files to set up newXlogId/newXlogSeg
+	 */
+	FindEndOfXLOG();
+
+	/*
 	 * Adjust fields if required by switches.  (Do this now so that printout,
 	 * if any, includes these values.)
 	 */
@@ -305,12 +311,12 @@ main(int argc, char *argv[])
 	if (minXlogTli > ControlFile.checkPointCopy.ThisTimeLineID)
 		ControlFile.checkPointCopy.ThisTimeLineID = minXlogTli;
 
-	if (minXlogId > ControlFile.logId ||
-		(minXlogId == ControlFile.logId &&
-		 minXlogSeg > ControlFile.logSeg))
+	if (minXlogId > newXlogId ||
+		(minXlogId == newXlogId &&
+		 minXlogSeg > newXlogSeg))
 	{
-		ControlFile.logId = minXlogId;
-		ControlFile.logSeg = minXlogSeg;
+		newXlogId = minXlogId;
+		newXlogSeg = minXlogSeg;
 	}
 
 	/*
@@ -469,8 +475,6 @@ GuessControlValues(void)
 
 	ControlFile.state = DB_SHUTDOWNED;
 	ControlFile.time = time(NULL);
-	ControlFile.logId = 0;
-	ControlFile.logSeg = 1;
 	ControlFile.checkPoint = ControlFile.checkPointCopy.redo;
 
 	ControlFile.maxAlign = MAXIMUM_ALIGNOF;
@@ -533,16 +537,16 @@ PrintControlValues(bool guessed)
 	snprintf(sysident_str, sizeof(sysident_str), UINT64_FORMAT,
 			 ControlFile.system_identifier);
 
+	printf(_("First log file ID for new XLOG:       %u\n"),
+		   newXlogId);
+	printf(_("First log file segment for new XLOG:  %u\n"),
+		   newXlogSeg);
 	printf(_("pg_control version number:            %u\n"),
 		   ControlFile.pg_control_version);
 	printf(_("Catalog version number:               %u\n"),
 		   ControlFile.catalog_version_no);
 	printf(_("Database system identifier:           %s\n"),
 		   sysident_str);
-	printf(_("Current log file ID:                  %u\n"),
-		   ControlFile.logId);
-	printf(_("Next log file segment:                %u\n"),
-		   ControlFile.logSeg);
 	printf(_("Latest checkpoint's TimeLineID:       %u\n"),
 		   ControlFile.checkPointCopy.ThisTimeLineID);
 	printf(_("Latest checkpoint's NextXID:          %u/%u\n"),
@@ -590,22 +594,9 @@ RewriteControlFile(void)
 	char		buffer[PG_CONTROL_SIZE];		/* need not be aligned */
 
 	/*
-	 * Adjust fields as needed to force an empty XLOG starting at the next
-	 * available segment.
+	 * Adjust fields as needed to force an empty XLOG starting at
+	 * newXlogId/newXlogSeg.
 	 */
-	newXlogId = ControlFile.logId;
-	newXlogSeg = ControlFile.logSeg;
-
-	/* adjust in case we are changing segment size */
-	newXlogSeg *= ControlFile.xlog_seg_size;
-	newXlogSeg = (newXlogSeg + XLogSegSize - 1) / XLogSegSize;
-
-	/* be sure we wrap around correctly at end of a logfile */
-	NextLogSeg(newXlogId, newXlogSeg);
-
-	/* Now we can force the recorded xlog seg size to the right thing. */
-	ControlFile.xlog_seg_size = XLogSegSize;
-
 	ControlFile.checkPointCopy.redo.xlogid = newXlogId;
 	ControlFile.checkPointCopy.redo.xrecoff =
 		newXlogSeg * XLogSegSize + SizeOfXLogLongPHD;
@@ -614,14 +605,15 @@ RewriteControlFile(void)
 
 	ControlFile.state = DB_SHUTDOWNED;
 	ControlFile.time = time(NULL);
-	ControlFile.logId = newXlogId;
-	ControlFile.logSeg = newXlogSeg + 1;
 	ControlFile.checkPoint = ControlFile.checkPointCopy.redo;
 	ControlFile.prevCheckPoint.xlogid = 0;
 	ControlFile.prevCheckPoint.xrecoff = 0;
 	ControlFile.minRecoveryPoint.xlogid = 0;
 	ControlFile.minRecoveryPoint.xrecoff = 0;
 
+	/* Now we can force the recorded xlog seg size to the right thing. */
+	ControlFile.xlog_seg_size = XLogSegSize;
+
 	/* Contents are protected with a CRC */
 	INIT_CRC32(ControlFile.crc);
 	COMP_CRC32(ControlFile.crc,
@@ -681,6 +673,97 @@ RewriteControlFile(void)
 
 
 /*
+ * Scan existing XLOG files and determine the highest existing WAL address
+ *
+ * On entry, ControlFile.checkPointCopy.redo and ControlFile.xlog_seg_size
+ * are assumed valid (note that we allow the old xlog seg size to differ
+ * from what we're using).  On exit, newXlogId and newXlogSeg are set to
+ * suitable values for the beginning of replacement WAL (in our seg size).
+ */
+static void
+FindEndOfXLOG(void)
+{
+	DIR		   *xldir;
+	struct dirent *xlde;
+
+	/*
+	 * Initialize the max() computation using the last checkpoint address
+	 * from old pg_control.  Note that for the moment we are working with
+	 * segment numbering according to the old xlog seg size.
+	 */
+	newXlogId = ControlFile.checkPointCopy.redo.xlogid;
+	newXlogSeg = ControlFile.checkPointCopy.redo.xrecoff / ControlFile.xlog_seg_size;
+
+	/*
+	 * Scan the pg_xlog directory to find existing WAL segment files.
+	 * We assume any present have been used; in most scenarios this should
+	 * be conservative, because of xlog.c's attempts to pre-create files.
+	 */
+	xldir = opendir(XLOGDIR);
+	if (xldir == NULL)
+	{
+		fprintf(stderr, _("%s: could not open directory \"%s\": %s\n"),
+				progname, XLOGDIR, strerror(errno));
+		exit(1);
+	}
+
+	errno = 0;
+	while ((xlde = readdir(xldir)) != NULL)
+	{
+		if (strlen(xlde->d_name) == 24 &&
+			strspn(xlde->d_name, "0123456789ABCDEF") == 24)
+		{
+			unsigned int	tli,
+							log,
+							seg;
+
+			sscanf(xlde->d_name, "%08X%08X%08X", &tli, &log, &seg);
+			/*
+			 * Note: we take the max of all files found, regardless of their
+			 * timelines.  Another possibility would be to ignore files of
+			 * timelines other than the target TLI, but this seems safer.
+			 * Better too large a result than too small...
+			 */
+			if (log > newXlogId ||
+				(log == newXlogId && seg > newXlogSeg))
+			{
+				newXlogId = log;
+				newXlogSeg = seg;
+			}
+		}
+		errno = 0;
+	}
+#ifdef WIN32
+
+	/*
+	 * This fix is in mingw cvs (runtime/mingwex/dirent.c rev 1.4), but not in
+	 * released version
+	 */
+	if (GetLastError() == ERROR_NO_MORE_FILES)
+		errno = 0;
+#endif
+
+	if (errno)
+	{
+		fprintf(stderr, _("%s: could not read from directory \"%s\": %s\n"),
+				progname, XLOGDIR, strerror(errno));
+		exit(1);
+	}
+	closedir(xldir);
+
+	/*
+	 * Finally, convert to new xlog seg size, and advance by one to ensure
+	 * we are in virgin territory.
+	 */
+	newXlogSeg *= ControlFile.xlog_seg_size;
+	newXlogSeg = (newXlogSeg + XLogSegSize - 1) / XLogSegSize;
+
+	/* be sure we wrap around correctly at end of a logfile */
+	NextLogSeg(newXlogId, newXlogSeg);
+}
+
+
+/*
  * Remove existing XLOG files
  */
 static void