Repair sometimes-incorrect computation of StartUpID after a crash, per

example from Rao Kumar.  This is a very corner corner-case, requiring
a minimum of three closely-spaced database crashes and an unlucky
positioning of the second recovery's checkpoint record before you'd notice
any problem.  But the consequences are dire enough that it's a must-fix.

diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index f68fc70..7fa2749 100644 (file)
--- 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 1.115 2003/05/10 18:01:31 tgl Exp $
+ * $Header: /cvsroot/pgsql/src/backend/access/transam/xlog.c,v 1.116 2003/05/22 14:39:28 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -2568,7 +2568,18 @@ StartupXLOG(void)
        ShmemVariableCache->nextOid = checkPoint.nextOid;
        ShmemVariableCache->oidCount = 0;
 
-       ThisStartUpID = checkPoint.ThisStartUpID;
+       /*
+        * If it was a shutdown checkpoint, then any following WAL entries were
+        * created under the next StartUpID; if it was a regular checkpoint then
+        * any following WAL entries were created under the same StartUpID.
+        * We must replay WAL entries using the same StartUpID they were created
+        * under, so temporarily adopt that SUI (see also xlog_redo()).
+        */
+       if (wasShutdown)
+               ThisStartUpID = checkPoint.ThisStartUpID + 1;
+       else
+               ThisStartUpID = checkPoint.ThisStartUpID;
+
        RedoRecPtr = XLogCtl->Insert.RedoRecPtr =
                XLogCtl->SavedRedoRecPtr = checkPoint.redo;
 
@@ -2672,55 +2683,21 @@ StartupXLOG(void)
        ControlFile->logSeg = openLogSeg + 1;
        Insert = &XLogCtl->Insert;
        Insert->PrevRecord = LastRec;
+       XLogCtl->xlblocks[0].xlogid = openLogId;
+       XLogCtl->xlblocks[0].xrecoff =
+               ((EndOfLog.xrecoff - 1) / BLCKSZ + 1) * BLCKSZ;
 
        /*
-        * If the next record will go to the new page then initialize for that
-        * one.
+        * Tricky point here: readBuf contains the *last* block that the
+        * LastRec record spans, not the one it starts in.      The last block
+        * is indeed the one we want to use.
         */
-       if ((BLCKSZ - EndOfLog.xrecoff % BLCKSZ) < SizeOfXLogRecord)
-               EndOfLog.xrecoff += (BLCKSZ - EndOfLog.xrecoff % BLCKSZ);
-       if (EndOfLog.xrecoff % BLCKSZ == 0)
-       {
-               XLogRecPtr      NewPageEndPtr;
-
-               NewPageEndPtr = EndOfLog;
-               if (NewPageEndPtr.xrecoff >= XLogFileSize)
-               {
-                       /* crossing a logid boundary */
-                       NewPageEndPtr.xlogid += 1;
-                       NewPageEndPtr.xrecoff = BLCKSZ;
-               }
-               else
-                       NewPageEndPtr.xrecoff += BLCKSZ;
-               XLogCtl->xlblocks[0] = NewPageEndPtr;
-               Insert->currpage->xlp_magic = XLOG_PAGE_MAGIC;
-               if (InRecovery)
-                       Insert->currpage->xlp_sui = ThisStartUpID;
-               else
-                       Insert->currpage->xlp_sui = ThisStartUpID + 1;
-               Insert->currpage->xlp_pageaddr.xlogid = NewPageEndPtr.xlogid;
-               Insert->currpage->xlp_pageaddr.xrecoff = NewPageEndPtr.xrecoff - BLCKSZ;
-               /* rest of buffer was zeroed in XLOGShmemInit */
-               Insert->currpos = (char *) Insert->currpage + SizeOfXLogPHD;
-       }
-       else
-       {
-               XLogCtl->xlblocks[0].xlogid = openLogId;
-               XLogCtl->xlblocks[0].xrecoff =
-                       ((EndOfLog.xrecoff - 1) / BLCKSZ + 1) * BLCKSZ;
-
-               /*
-                * Tricky point here: readBuf contains the *last* block that the
-                * LastRec record spans, not the one it starts in.      The last block
-                * is indeed the one we want to use.
-                */
-               Assert(readOff == (XLogCtl->xlblocks[0].xrecoff - BLCKSZ) % XLogSegSize);
-               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));
-       }
+       Assert(readOff == (XLogCtl->xlblocks[0].xrecoff - BLCKSZ) % XLogSegSize);
+       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;
 
@@ -2775,8 +2752,21 @@ StartupXLOG(void)
                MyXactMadeTempRelUpdate = false;
 
                /*
+                * At this point, ThisStartUpID is the largest SUI that we could
+                * find evidence for in the WAL entries.  But check it against
+                * pg_control's latest checkpoint, to make sure that we can't
+                * accidentally re-use an already-used SUI.
+                */
+               if (ThisStartUpID < ControlFile->checkPointCopy.ThisStartUpID)
+                       ThisStartUpID = ControlFile->checkPointCopy.ThisStartUpID;
+
+               /*
                 * Perform a new checkpoint to update our recovery activity to disk.
                 *
+                * Note that we write a shutdown checkpoint.  This is correct since
+                * the records following it will use SUI one more than what is shown
+                * in the checkpoint's ThisStartUpID.
+                *
                 * In case we had to use the secondary checkpoint, make sure that
                 * it will still be shown as the secondary checkpoint after this
                 * CreateCheckPoint operation; we don't want the broken primary
@@ -2790,21 +2780,39 @@ StartupXLOG(void)
                 */
                XLogCloseRelationCache();
        }
+       else
+       {
+               /*
+                * If we are not doing recovery, then we saw a checkpoint with nothing
+                * after it, and we can safely use StartUpID equal to one more than
+                * the checkpoint's SUI.  But just for paranoia's sake, check against
+                * pg_control too.
+                */
+               ThisStartUpID = checkPoint.ThisStartUpID;
+               if (ThisStartUpID < ControlFile->checkPointCopy.ThisStartUpID)
+                       ThisStartUpID = ControlFile->checkPointCopy.ThisStartUpID;
+       }
 
        /*
         * Preallocate additional log files, if wanted.
         */
        PreallocXlogFiles(EndOfLog);
 
+       /*
+        * Advance StartUpID to one more than the highest value used previously.
+        */
+       ThisStartUpID++;
+       XLogCtl->ThisStartUpID = ThisStartUpID;
+
+       /*
+        * Okay, we're officially UP.
+        */
        InRecovery = false;
 
        ControlFile->state = DB_IN_PRODUCTION;
        ControlFile->time = time(NULL);
        UpdateControlFile();
 
-       ThisStartUpID++;
-       XLogCtl->ThisStartUpID = ThisStartUpID;
-
        /* Start up the commit log, too */
        StartupCLOG();
 
@@ -3000,7 +3008,7 @@ CreateCheckPoint(bool shutdown, bool force)
                UpdateControlFile();
        }
 
-       memset(&checkPoint, 0, sizeof(checkPoint));
+       MemSet(&checkPoint, 0, sizeof(checkPoint));
        checkPoint.ThisStartUpID = ThisStartUpID;
        checkPoint.time = time(NULL);
 
@@ -3259,6 +3267,8 @@ xlog_redo(XLogRecPtr lsn, XLogRecord *record)
                ShmemVariableCache->nextXid = checkPoint.nextXid;
                ShmemVariableCache->nextOid = checkPoint.nextOid;
                ShmemVariableCache->oidCount = 0;
+               /* Any later WAL records should be run with shutdown SUI plus 1 */
+               ThisStartUpID = checkPoint.ThisStartUpID + 1;
        }
        else if (info == XLOG_CHECKPOINT_ONLINE)
        {
@@ -3274,6 +3284,8 @@ xlog_redo(XLogRecPtr lsn, XLogRecord *record)
                        ShmemVariableCache->nextOid = checkPoint.nextOid;
                        ShmemVariableCache->oidCount = 0;
                }
+               /* Any later WAL records should be run with the then-active SUI */
+               ThisStartUpID = checkPoint.ThisStartUpID;
        }
 }