Fix TransactionIdSetStatusBit so that it doesn't try to change a transaction

from COMMITTED to SUBCOMMITTED during recovery.  This wasn't previously
possible, but it is now due to the recent changes on clog commit protocol for
subtransactions.

Simon Riggs

diff --git a/src/backend/access/transam/clog.c b/src/backend/access/transam/clog.c
index fcff3ea3cfdaf73900aebbdf3138b7601baae8cf..3d62417387b33cca2451df7fe3bb3b526b61a0e8 100644 (file)
--- a/src/backend/access/transam/clog.c
+++ b/src/backend/access/transam/clog.c
@@ -26,7 +26,7 @@
  * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/backend/access/transam/clog.c,v 1.48 2008/10/20 19:18:18 alvherre Exp $
+ * $PostgreSQL: pgsql/src/backend/access/transam/clog.c,v 1.49 2008/11/03 19:24:03 alvherre Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -321,13 +321,29 @@ TransactionIdSetStatusBit(TransactionId xid, XidStatus status, XLogRecPtr lsn, i
    int         bshift = TransactionIdToBIndex(xid) * CLOG_BITS_PER_XACT;
    char       *byteptr;
    char        byteval;
+   char        curval;
 
    byteptr = ClogCtl->shared->page_buffer[slotno] + byteno;
+   curval = (*byteptr >> shift) & CLOG_XACT_BITMASK;
 
-   /* Current state should be 0, subcommitted or target state */
-   Assert(((*byteptr >> bshift) & CLOG_XACT_BITMASK) == 0 ||
-          ((*byteptr >> bshift) & CLOG_XACT_BITMASK) == TRANSACTION_STATUS_SUB_COMMITTED ||
-          ((*byteptr >> bshift) & CLOG_XACT_BITMASK) == status);
+   /*
+    * When replaying transactions during recovery we still need to perform
+    * the two phases of subcommit and then commit. However, some transactions
+    * are already correctly marked, so we just treat those as a no-op which
+    * allows us to keep the following Assert as restrictive as possible.
+    */
+   if (InRecovery && status == TRANSACTION_STATUS_SUB_COMMITTED &&
+       curval == TRANSACTION_STATUS_COMMITTED)
+       return;
+
+   /* 
+    * Current state change should be from 0 or subcommitted to target state
+    * or we should already be there when replaying changes during recovery.
+    */
+   Assert(curval == 0 ||
+          (curval == TRANSACTION_STATUS_SUB_COMMITTED &&
+           status != TRANSACTION_STATUS_IN_PROGRESS) ||
+          curval == status);
 
    /* note this assumes exclusive access to the clog page */
    byteval = *byteptr;