Fix handling of orphaned 2PC files in the future at recovery

Before 728bd991c3c4, that has improved the support for 2PC files during
recovery, the initial logic scanning files in pg_twophase was done so as
files in the future of the transaction ID horizon were checked first,
followed by a check if a transaction ID is aborted or committed which
could involve a pg_xact lookup.  After this commit, these checks have
been done in reverse order.

Files detected as in the future do not have a state that can be checked
in pg_xact, hence this caused recovery to fail abruptly should an
orphaned 2PC file in the future of the transaction ID horizon exist in
pg_twophase at the beginning of recovery.

A test is added to check for this scenario, using an empty 2PC with a
transaction ID large enough to be in the future when running the test.
This test is added in 16 and older versions for now.  17 and newer
versions are impacted by a second bug caused by the addition of the
epoch in the 2PC file names.  An equivalent test will be added in these
branches in a follow-up commit, once the second set of issues reported
are fixed.

Author: Vitaly Davydov, Michael Paquier
Discussion: https://postgr.es/m/11e597-676ab680-8d-374f23c0@145466129
Back-through: 13

diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index 0a0932cff44a24be53360dcfa339cd47d91395d1..1df2731ecb4de7064d39a849ff94f5b802e2046c 100644 (file)
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -2167,40 +2167,40 @@ ProcessTwoPhaseBuffer(TransactionId xid,
    if (!fromdisk)
        Assert(prepare_start_lsn != InvalidXLogRecPtr);
 
-   /* Already processed? */
-   if (TransactionIdDidCommit(xid) || TransactionIdDidAbort(xid))
+   /* Reject XID if too new */
+   if (TransactionIdFollowsOrEquals(xid, origNextXid))
    {
        if (fromdisk)
        {
            ereport(WARNING,
-                   (errmsg("removing stale two-phase state file for transaction %u",
+                   (errmsg("removing future two-phase state file for transaction %u",
                            xid)));
            RemoveTwoPhaseFile(xid, true);
        }
        else
        {
            ereport(WARNING,
-                   (errmsg("removing stale two-phase state from memory for transaction %u",
+                   (errmsg("removing future two-phase state from memory for transaction %u",
                            xid)));
            PrepareRedoRemove(xid, true);
        }
        return NULL;
    }
 
-   /* Reject XID if too new */
-   if (TransactionIdFollowsOrEquals(xid, origNextXid))
+   /* Already processed? */
+   if (TransactionIdDidCommit(xid) || TransactionIdDidAbort(xid))
    {
        if (fromdisk)
        {
            ereport(WARNING,
-                   (errmsg("removing future two-phase state file for transaction %u",
+                   (errmsg("removing stale two-phase state file for transaction %u",
                            xid)));
            RemoveTwoPhaseFile(xid, true);
        }
        else
        {
            ereport(WARNING,
-                   (errmsg("removing future two-phase state from memory for transaction %u",
+                   (errmsg("removing stale two-phase state from memory for transaction %u",
                            xid)));
            PrepareRedoRemove(xid, true);
        }