Temporarily dike out GetUndoRecPtr() in checkpoint generation, since we

do not use the undo pointer anyway.  This is a quick-hack solution for
the three-way deadlock condition discussed in pghackers 17-Dec-01.
Need to find a better way of doing it.

diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 11bc02e1a9986709234dab1bbf167a1119eeb6b7..57a0fbcc69fb45da524424f78f8765d23b66f125 100644 (file)
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2001, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $Header: /cvsroot/pgsql/src/backend/access/transam/xlog.c,v 1.82 2001/11/05 17:46:24 momjian Exp $
+ * $Header: /cvsroot/pgsql/src/backend/access/transam/xlog.c,v 1.83 2001/12/19 19:42:51 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -744,9 +744,13 @@ begin:;
        /* If first XLOG record of transaction, save it in PROC array */
        if (MyLastRecPtr.xrecoff == 0 && !no_tran)
        {
-               LWLockAcquire(SInvalLock, LW_EXCLUSIVE);
+               /*
+                * We do not acquire SInvalLock here because of possible deadlock.
+                * Anyone who wants to inspect other procs' logRec must acquire
+                * WALInsertLock, instead.  A better solution would be a per-PROC
+                * spinlock, but no time for that before 7.2 --- tgl 12/19/01.
+                */
                MyProc->logRec = RecPtr;
-               LWLockRelease(SInvalLock);
        }
 
        if (XLOG_DEBUG)
@@ -2928,11 +2932,22 @@ CreateCheckPoint(bool shutdown)
         * this while holding insert lock to ensure that we won't miss any
         * about-to-commit transactions (UNDO must include all xacts that have
         * commits after REDO point).
+        *
+        * XXX temporarily ifdef'd out to avoid three-way deadlock condition:
+        * GetUndoRecPtr needs to grab SInvalLock to ensure that it is looking
+        * at a stable set of proc records, but grabbing SInvalLock while holding
+        * WALInsertLock is no good.  GetNewTransactionId may cause a WAL record
+        * to be written while holding XidGenLock, and GetSnapshotData needs to
+        * get XidGenLock while holding SInvalLock, so there's a risk of deadlock.
+        * Need to find a better solution.  See pgsql-hackers discussion of
+        * 17-Dec-01.
         */
+#ifdef NOT_USED
        checkPoint.undo = GetUndoRecPtr();
 
        if (shutdown && checkPoint.undo.xrecoff != 0)
                elog(STOP, "active transaction while database system is shutting down");
+#endif
 
        /*
         * Now we can release insert lock, allowing other xacts to proceed