Correctly detect SSI conflicts of prepared transactions after crash.

A prepared transaction can get new conflicts in and out after preparing, so
we cannot rely on the in- and out-flags stored in the statefile at prepare-
time. As a quick fix, make the conservative assumption that after a restart,
all prepared transactions are considered to have both in- and out-conflicts.
That can lead to unnecessary rollbacks after a crash, but that shouldn't be
a big problem in practice; you don't want prepared transactions to hang
around for a long time anyway.

Dan Ports

diff --git a/src/backend/storage/lmgr/predicate.c b/src/backend/storage/lmgr/predicate.c
index 9e927f8564451b215c49a0a1b3a2961e704f55ca..08fb69c32e5ccd393afd1333cb32fe460e77cbfd 100644 (file)
--- a/src/backend/storage/lmgr/predicate.c
+++ b/src/backend/storage/lmgr/predicate.c
@@ -4730,14 +4730,11 @@ AtPrepare_PredicateLocks(void)
    xactRecord->flags = MySerializableXact->flags;
 
    /*
-    * Tweak the flags. Since we're not going to output the inConflicts and
-    * outConflicts lists, if they're non-empty we'll represent that by
-    * setting the appropriate summary conflict flags.
+    * Note that we don't include the list of conflicts in our out in
+    * the statefile, because new conflicts can be added even after the
+    * transaction prepares. We'll just make a conservative assumption
+    * during recovery instead.
     */
-   if (!SHMQueueEmpty(&MySerializableXact->inConflicts))
-       xactRecord->flags |= SXACT_FLAG_SUMMARY_CONFLICT_IN;
-   if (!SHMQueueEmpty(&MySerializableXact->outConflicts))
-       xactRecord->flags |= SXACT_FLAG_SUMMARY_CONFLICT_OUT;
 
    RegisterTwoPhaseRecord(TWOPHASE_RM_PREDICATELOCK_ID, 0,
                           &record, sizeof(record));
@@ -4872,15 +4869,6 @@ predicatelock_twophase_recover(TransactionId xid, uint16 info,
 
        sxact->SeqNo.lastCommitBeforeSnapshot = RecoverySerCommitSeqNo;
 
-
-       /*
-        * We don't need the details of a prepared transaction's conflicts,
-        * just whether it had conflicts in or out (which we get from the
-        * flags)
-        */
-       SHMQueueInit(&(sxact->outConflicts));
-       SHMQueueInit(&(sxact->inConflicts));
-
        /*
         * Don't need to track this; no transactions running at the time the
         * recovered xact started are still active, except possibly other
@@ -4902,6 +4890,17 @@ predicatelock_twophase_recover(TransactionId xid, uint16 info,
                   (MaxBackends + max_prepared_xacts));
        }
 
+       /*
+        * We don't know whether the transaction had any conflicts or
+        * not, so we'll conservatively assume that it had both a
+        * conflict in and a conflict out, and represent that with the
+        * summary conflict flags.
+        */
+       SHMQueueInit(&(sxact->outConflicts));
+       SHMQueueInit(&(sxact->inConflicts));
+       sxact->flags |= SXACT_FLAG_SUMMARY_CONFLICT_IN;
+       sxact->flags |= SXACT_FLAG_SUMMARY_CONFLICT_OUT;
+
        /* Register the transaction's xid */
        sxidtag.xid = xid;
        sxid = (SERIALIZABLEXID *) hash_search(SerializableXidHash,