Adjust time qual checking code so that we always check TransactionIdIsInProgress

before we check commit/abort status.  Formerly this was done in some paths
but not all, with the result that a transaction might be considered
committed for some purposes before it became committed for others.
Per example found by Jan Wieck.

diff --git a/src/backend/utils/time/tqual.c b/src/backend/utils/time/tqual.c
index 916d840ea34320e79c58359dea9b0cc19f9fb8a6..c66a3d0e1f799f770194977fcae6ff576eca93ce 100644 (file)
--- a/src/backend/utils/time/tqual.c
+++ b/src/backend/utils/time/tqual.c
@@ -11,12 +11,28 @@
  * "hint" status bits if we see that the inserting or deleting transaction
  * has now committed or aborted.
  *
+ * NOTE: must check TransactionIdIsInProgress (which looks in PGPROC array)
+ * before TransactionIdDidCommit/TransactionIdDidAbort (which look in
+ * pg_clog).  Otherwise we have a race condition: we might decide that a
+ * just-committed transaction crashed, because none of the tests succeed.
+ * xact.c is careful to record commit/abort in pg_clog before it unsets
+ * MyProc->xid in PGPROC array.  That fixes that problem, but it also
+ * means there is a window where TransactionIdIsInProgress and
+ * TransactionIdDidCommit will both return true.  If we check only
+ * TransactionIdDidCommit, we could consider a tuple committed when a
+ * later GetSnapshotData call will still think the originating transaction
+ * is in progress, which leads to application-level inconsistency.  The
+ * upshot is that we gotta check TransactionIdIsInProgress first in all
+ * code paths, except for a few cases where we are looking at
+ * subtransactions of our own main transaction and so there can't be any
+ * race condition.
+ *
  *
  * Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *   $PostgreSQL: pgsql/src/backend/utils/time/tqual.c,v 1.87 2005/04/28 21:47:16 tgl Exp $
+ *   $PostgreSQL: pgsql/src/backend/utils/time/tqual.c,v 1.88 2005/05/07 21:22:01 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -147,19 +163,19 @@ HeapTupleSatisfiesItself(HeapTupleHeader tuple, Buffer buffer)
 
            return false;
        }
-       else if (!TransactionIdDidCommit(HeapTupleHeaderGetXmin(tuple)))
-       {
-           if (TransactionIdDidAbort(HeapTupleHeaderGetXmin(tuple)))
-           {
-               tuple->t_infomask |= HEAP_XMIN_INVALID;
-               SetBufferCommitInfoNeedsSave(buffer);
-           }
+       else if (TransactionIdIsInProgress(HeapTupleHeaderGetXmin(tuple)))
            return false;
+       else if (TransactionIdDidCommit(HeapTupleHeaderGetXmin(tuple)))
+       {
+           tuple->t_infomask |= HEAP_XMIN_COMMITTED;
+           SetBufferCommitInfoNeedsSave(buffer);
        }
        else
        {
-           tuple->t_infomask |= HEAP_XMIN_COMMITTED;
+           /* it must have aborted or crashed */
+           tuple->t_infomask |= HEAP_XMIN_INVALID;
            SetBufferCommitInfoNeedsSave(buffer);
+           return false;
        }
    }
 
@@ -189,13 +205,14 @@ HeapTupleSatisfiesItself(HeapTupleHeader tuple, Buffer buffer)
        return false;
    }
 
+   if (TransactionIdIsInProgress(HeapTupleHeaderGetXmax(tuple)))
+       return true;
+
    if (!TransactionIdDidCommit(HeapTupleHeaderGetXmax(tuple)))
    {
-       if (TransactionIdDidAbort(HeapTupleHeaderGetXmax(tuple)))
-       {
-           tuple->t_infomask |= HEAP_XMAX_INVALID;
-           SetBufferCommitInfoNeedsSave(buffer);
-       }
+       /* it must have aborted or crashed */
+       tuple->t_infomask |= HEAP_XMAX_INVALID;
+       SetBufferCommitInfoNeedsSave(buffer);
        return true;
    }
 
@@ -330,19 +347,19 @@ HeapTupleSatisfiesNow(HeapTupleHeader tuple, Buffer buffer)
            else
                return false;   /* deleted before scan started */
        }
-       else if (!TransactionIdDidCommit(HeapTupleHeaderGetXmin(tuple)))
-       {
-           if (TransactionIdDidAbort(HeapTupleHeaderGetXmin(tuple)))
-           {
-               tuple->t_infomask |= HEAP_XMIN_INVALID;
-               SetBufferCommitInfoNeedsSave(buffer);
-           }
+       else if (TransactionIdIsInProgress(HeapTupleHeaderGetXmin(tuple)))
            return false;
+       else if (TransactionIdDidCommit(HeapTupleHeaderGetXmin(tuple)))
+       {
+           tuple->t_infomask |= HEAP_XMIN_COMMITTED;
+           SetBufferCommitInfoNeedsSave(buffer);
        }
        else
        {
-           tuple->t_infomask |= HEAP_XMIN_COMMITTED;
+           /* it must have aborted or crashed */
+           tuple->t_infomask |= HEAP_XMIN_INVALID;
            SetBufferCommitInfoNeedsSave(buffer);
+           return false;
        }
    }
 
@@ -375,13 +392,14 @@ HeapTupleSatisfiesNow(HeapTupleHeader tuple, Buffer buffer)
            return false;       /* deleted before scan started */
    }
 
+   if (TransactionIdIsInProgress(HeapTupleHeaderGetXmax(tuple)))
+       return true;
+
    if (!TransactionIdDidCommit(HeapTupleHeaderGetXmax(tuple)))
    {
-       if (TransactionIdDidAbort(HeapTupleHeaderGetXmax(tuple)))
-       {
-           tuple->t_infomask |= HEAP_XMAX_INVALID;
-           SetBufferCommitInfoNeedsSave(buffer);
-       }
+       /* it must have aborted or crashed */
+       tuple->t_infomask |= HEAP_XMAX_INVALID;
+       SetBufferCommitInfoNeedsSave(buffer);
        return true;
    }
 
@@ -569,19 +587,19 @@ HeapTupleSatisfiesUpdate(HeapTupleHeader tuple, CommandId curcid,
                return HeapTupleInvisible;      /* updated before scan
                                                 * started */
        }
-       else if (!TransactionIdDidCommit(HeapTupleHeaderGetXmin(tuple)))
-       {
-           if (TransactionIdDidAbort(HeapTupleHeaderGetXmin(tuple)))
-           {
-               tuple->t_infomask |= HEAP_XMIN_INVALID;
-               SetBufferCommitInfoNeedsSave(buffer);
-           }
+       else if (TransactionIdIsInProgress(HeapTupleHeaderGetXmin(tuple)))
            return HeapTupleInvisible;
+       else if (TransactionIdDidCommit(HeapTupleHeaderGetXmin(tuple)))
+       {
+           tuple->t_infomask |= HEAP_XMIN_COMMITTED;
+           SetBufferCommitInfoNeedsSave(buffer);
        }
        else
        {
-           tuple->t_infomask |= HEAP_XMIN_COMMITTED;
+           /* it must have aborted or crashed */
+           tuple->t_infomask |= HEAP_XMIN_INVALID;
            SetBufferCommitInfoNeedsSave(buffer);
+           return HeapTupleInvisible;
        }
    }
 
@@ -620,16 +638,15 @@ HeapTupleSatisfiesUpdate(HeapTupleHeader tuple, CommandId curcid,
            return HeapTupleInvisible;  /* updated before scan started */
    }
 
+   if (TransactionIdIsInProgress(HeapTupleHeaderGetXmax(tuple)))
+       return HeapTupleBeingUpdated;
+
    if (!TransactionIdDidCommit(HeapTupleHeaderGetXmax(tuple)))
    {
-       if (TransactionIdDidAbort(HeapTupleHeaderGetXmax(tuple)))
-       {
-           tuple->t_infomask |= HEAP_XMAX_INVALID;
-           SetBufferCommitInfoNeedsSave(buffer);
-           return HeapTupleMayBeUpdated;
-       }
-       /* running xact */
-       return HeapTupleBeingUpdated;   /* in updation by other */
+       /* it must have aborted or crashed */
+       tuple->t_infomask |= HEAP_XMAX_INVALID;
+       SetBufferCommitInfoNeedsSave(buffer);
+       return HeapTupleMayBeUpdated;
    }
 
    /* xmax transaction committed */
@@ -735,23 +752,24 @@ HeapTupleSatisfiesDirty(HeapTupleHeader tuple, Buffer buffer)
 
            return false;
        }
-       else if (!TransactionIdDidCommit(HeapTupleHeaderGetXmin(tuple)))
+       else if (TransactionIdIsInProgress(HeapTupleHeaderGetXmin(tuple)))
        {
-           if (TransactionIdDidAbort(HeapTupleHeaderGetXmin(tuple)))
-           {
-               tuple->t_infomask |= HEAP_XMIN_INVALID;
-               SetBufferCommitInfoNeedsSave(buffer);
-               return false;
-           }
            SnapshotDirty->xmin = HeapTupleHeaderGetXmin(tuple);
            /* XXX shouldn't we fall through to look at xmax? */
            return true;        /* in insertion by other */
        }
-       else
+       else if (TransactionIdDidCommit(HeapTupleHeaderGetXmin(tuple)))
        {
            tuple->t_infomask |= HEAP_XMIN_COMMITTED;
            SetBufferCommitInfoNeedsSave(buffer);
        }
+       else
+       {
+           /* it must have aborted or crashed */
+           tuple->t_infomask |= HEAP_XMIN_INVALID;
+           SetBufferCommitInfoNeedsSave(buffer);
+           return false;
+       }
    }
 
    /* by here, the inserting transaction has committed */
@@ -781,17 +799,18 @@ HeapTupleSatisfiesDirty(HeapTupleHeader tuple, Buffer buffer)
        return false;
    }
 
-   if (!TransactionIdDidCommit(HeapTupleHeaderGetXmax(tuple)))
+   if (TransactionIdIsInProgress(HeapTupleHeaderGetXmax(tuple)))
    {
-       if (TransactionIdDidAbort(HeapTupleHeaderGetXmax(tuple)))
-       {
-           tuple->t_infomask |= HEAP_XMAX_INVALID;
-           SetBufferCommitInfoNeedsSave(buffer);
-           return true;
-       }
-       /* running xact */
        SnapshotDirty->xmax = HeapTupleHeaderGetXmax(tuple);
-       return true;            /* in updation by other */
+       return true;
+   }
+
+   if (!TransactionIdDidCommit(HeapTupleHeaderGetXmax(tuple)))
+   {
+       /* it must have aborted or crashed */
+       tuple->t_infomask |= HEAP_XMAX_INVALID;
+       SetBufferCommitInfoNeedsSave(buffer);
+       return true;
    }
 
    /* xmax transaction committed */
@@ -907,19 +926,19 @@ HeapTupleSatisfiesSnapshot(HeapTupleHeader tuple, Snapshot snapshot,
            else
                return false;   /* deleted before scan started */
        }
-       else if (!TransactionIdDidCommit(HeapTupleHeaderGetXmin(tuple)))
-       {
-           if (TransactionIdDidAbort(HeapTupleHeaderGetXmin(tuple)))
-           {
-               tuple->t_infomask |= HEAP_XMIN_INVALID;
-               SetBufferCommitInfoNeedsSave(buffer);
-           }
+       else if (TransactionIdIsInProgress(HeapTupleHeaderGetXmin(tuple)))
            return false;
+       else if (TransactionIdDidCommit(HeapTupleHeaderGetXmin(tuple)))
+       {
+           tuple->t_infomask |= HEAP_XMIN_COMMITTED;
+           SetBufferCommitInfoNeedsSave(buffer);
        }
        else
        {
-           tuple->t_infomask |= HEAP_XMIN_COMMITTED;
+           /* it must have aborted or crashed */
+           tuple->t_infomask |= HEAP_XMIN_INVALID;
            SetBufferCommitInfoNeedsSave(buffer);
+           return false;
        }
    }
 
@@ -982,13 +1001,14 @@ HeapTupleSatisfiesSnapshot(HeapTupleHeader tuple, Snapshot snapshot,
                return false;   /* deleted before scan started */
        }
 
+       if (TransactionIdIsInProgress(HeapTupleHeaderGetXmax(tuple)))
+           return true;
+
        if (!TransactionIdDidCommit(HeapTupleHeaderGetXmax(tuple)))
        {
-           if (TransactionIdDidAbort(HeapTupleHeaderGetXmax(tuple)))
-           {
-               tuple->t_infomask |= HEAP_XMAX_INVALID;
-               SetBufferCommitInfoNeedsSave(buffer);
-           }
+           /* it must have aborted or crashed */
+           tuple->t_infomask |= HEAP_XMAX_INVALID;
+           SetBufferCommitInfoNeedsSave(buffer);
            return true;
        }
 
@@ -1057,13 +1077,6 @@ HeapTupleSatisfiesVacuum(HeapTupleHeader tuple, TransactionId OldestXmin,
     *
     * If the inserting transaction aborted, then the tuple was never visible
     * to any other transaction, so we can delete it immediately.
-    *
-    * NOTE: must check TransactionIdIsInProgress (which looks in PROC array)
-    * before TransactionIdDidCommit/TransactionIdDidAbort (which look in
-    * pg_clog).  Otherwise we have a race condition where we might decide
-    * that a just-committed transaction crashed, because none of the
-    * tests succeed.  xact.c is careful to record commit/abort in pg_clog
-    * before it unsets MyProc->xid in PROC array.
     */
    if (!(tuple->t_infomask & HEAP_XMIN_COMMITTED))
    {