Repair boundary-case bug introduced by patch of two months ago that

tglsfdc · tglsfdc · commit 8cf63ba920ea · 2003-07-17T16:45:04.000Z
fixed incorrect initial setting of StartUpID.  The logic in XLogWrite()
expects that Write-&gt;curridx is advanced to the next page as soon as
LogwrtResult points to the end of the current page, but StartupXLOG()
failed to make that happen when the old WAL ended exactly on a page
boundary.  Per trouble report from Hannu Krosing.
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2002, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $Header: /cvsroot/pgsql/src/backend/access/transam/xlog.c,v 1.117 2003/06/26 18:23:07 tgl Exp $
+ * $Header: /cvsroot/pgsql/src/backend/access/transam/xlog.c,v 1.118 2003/07/17 16:45:04 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -2487,6 +2487,7 @@ StartupXLOG(void)
 				EndOfLog;
 	XLogRecord *record;
 	char	   *buffer;
+	uint32		freespace;
 
 	/* Use malloc() to ensure record buffer is MAXALIGNED */
 	buffer = (char *) malloc(_INTL_MAXLOGRECSZ);
@@ -2697,8 +2698,6 @@ StartupXLOG(void)
 	memcpy((char *) Insert->currpage, readBuf, BLCKSZ);
 	Insert->currpos = (char *) Insert->currpage +
 		(EndOfLog.xrecoff + BLCKSZ - XLogCtl->xlblocks[0].xrecoff);
-	/* Make sure rest of page is zero */
-	MemSet(Insert->currpos, 0, INSERT_FREESPACE(Insert));
 
 	LogwrtResult.Write = LogwrtResult.Flush = EndOfLog;
 
@@ -2709,6 +2708,27 @@ StartupXLOG(void)
 	XLogCtl->LogwrtRqst.Write = EndOfLog;
 	XLogCtl->LogwrtRqst.Flush = EndOfLog;
 
+	freespace = INSERT_FREESPACE(Insert);
+	if (freespace > 0)
+	{
+		/* Make sure rest of page is zero */
+		MemSet(Insert->currpos, 0, freespace);
+		XLogCtl->Write.curridx = 0;
+	}
+	else
+	{
+		/*
+		 * Whenever Write.LogwrtResult points to exactly the end of a page,
+		 * Write.curridx must point to the *next* page (see XLogWrite()).
+		 *
+		 * Note: it might seem we should do AdvanceXLInsertBuffer() here,
+		 * but we can't since we haven't yet determined the correct StartUpID
+		 * to put into the new page's header.  The first actual attempt to
+		 * insert a log record will advance the insert state.
+		 */
+		XLogCtl->Write.curridx = NextBufIdx(0);
+	}
+
 #ifdef NOT_USED
 	/* UNDO */
 	if (InRecovery)
