Adjust CreateCheckpoint so that buffer dumping activities and cleanup of

dead xlog segments are not considered part of a critical section.  It is
not necessary to force a database-wide panic if we get a failure in these
operations.  Per recent trouble reports.

diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index d1523dc89b038177f0e718d5cd7a1b6adea5658a..f68fc7053669851eb381646c6b87ea533804dd9a 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 1.114 2003/04/25 19:45:08 tgl Exp $
+ * $Header: /cvsroot/pgsql/src/backend/access/transam/xlog.c,v 1.115 2003/05/10 18:01:31 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -2973,11 +2973,13 @@ CreateCheckPoint(bool shutdown, bool force)
        elog(ERROR, "CreateCheckPoint: cannot be called inside transaction block");
 
    /*
+    * Acquire CheckpointLock to ensure only one checkpoint happens at a time.
+    *
     * The CheckpointLock can be held for quite a while, which is not good
     * because we won't respond to a cancel/die request while waiting for
     * an LWLock.  (But the alternative of using a regular lock won't work
     * for background checkpoint processes, which are not regular
-    * backends.) So, rather than use a plain LWLockAcquire, use this
+    * backends.)  So, rather than use a plain LWLockAcquire, use this
     * kluge to allow an interrupt to be accepted while we are waiting:
     */
    while (!LWLockConditionalAcquire(CheckpointLock, LW_EXCLUSIVE))
@@ -2986,6 +2988,9 @@ CreateCheckPoint(bool shutdown, bool force)
        sleep(1);
    }
 
+   /*
+    * Use a critical section to force system panic if we have trouble.
+    */
    START_CRIT_SECTION();
 
    if (shutdown)
@@ -3056,6 +3061,13 @@ CreateCheckPoint(bool shutdown, bool force)
    /*
     * Here we update the shared RedoRecPtr for future XLogInsert calls;
     * this must be done while holding the insert lock AND the info_lck.
+    *
+    * Note: if we fail to complete the checkpoint, RedoRecPtr will be
+    * left pointing past where it really needs to point.  This is okay;
+    * the only consequence is that XLogInsert might back up whole buffers
+    * that it didn't really need to.  We can't postpone advancing RedoRecPtr
+    * because XLogInserts that happen while we are dumping buffers must
+    * assume that their buffer changes are not included in the checkpoint.
     */
    {
        /* use volatile pointer to prevent code rearrangement */
@@ -3094,6 +3106,9 @@ CreateCheckPoint(bool shutdown, bool force)
     */
    LWLockRelease(WALInsertLock);
 
+   /*
+    * Get the other info we need for the checkpoint record.
+    */
    LWLockAcquire(XidGenLock, LW_SHARED);
    checkPoint.nextXid = ShmemVariableCache->nextXid;
    LWLockRelease(XidGenLock);
@@ -3107,10 +3122,18 @@ CreateCheckPoint(bool shutdown, bool force)
    /*
     * Having constructed the checkpoint record, ensure all shmem disk
     * buffers and commit-log buffers are flushed to disk.
+    *
+    * This I/O could fail for various reasons.  If so, we will fail to
+    * complete the checkpoint, but there is no reason to force a system
+    * panic.  Accordingly, exit critical section while doing it.
     */
+   END_CRIT_SECTION();
+
    CheckPointCLOG();
    FlushBufferPool();
 
+   START_CRIT_SECTION();
+
    /*
     * Now insert the checkpoint record into XLOG.
     */
@@ -3166,6 +3189,12 @@ CreateCheckPoint(bool shutdown, bool force)
    UpdateControlFile();
    LWLockRelease(ControlFileLock);
 
+   /*
+    * We are now done with critical updates; no need for system panic if
+    * we have trouble while fooling with offline log segments.
+    */
+   END_CRIT_SECTION();
+
    /*
     * Delete offline log files (those no longer needed even for previous
     * checkpoint).
@@ -3185,8 +3214,6 @@ CreateCheckPoint(bool shutdown, bool force)
        PreallocXlogFiles(recptr);
 
    LWLockRelease(CheckpointLock);
-
-   END_CRIT_SECTION();
 }
 
 /*