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))
        {