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Simplify multixact freezing a bit 

Testing for abortedness of a multixact member that's being frozen is
unnecessary: we only need to know whether the transaction is still in
progress or committed to determine whether it must be kept or not.  This
let us simplify the code a bit and avoid a useless TransactionIdDidAbort
test.

Suggested by Andres Freund awhile back.
This commit is contained in:
Alvaro Herrera 2014-07-29 15:40:55 -04:00
parent 60d931827b
commit c2581794f3
1 changed files with 23 additions and 33 deletions
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56
src/backend/access/heap/heapam.c
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@ -5627,17 +5627,13 @@ FreezeMultiXactId(MultiXactId multi, uint16 t_infomask,
/*
* It's an update; should we keep it? If the transaction is known
* aborted then it's okay to ignore it, otherwise not. However,
* if the Xid is older than the cutoff_xid, we must remove it.
* Note that such an old updater cannot possibly be committed,
* because HeapTupleSatisfiesVacuum would have returned
* aborted or crashed then it's okay to ignore it, otherwise not.
* Note that an updater older than cutoff_xid cannot possibly be
* committed, because HeapTupleSatisfiesVacuum would have returned
* HEAPTUPLE_DEAD and we would not be trying to freeze the tuple.
*
* Note the TransactionIdDidAbort() test is just an optimization
* and not strictly necessary for correctness.
*
* As with all tuple visibility routines, it's critical to test
* TransactionIdIsInProgress before the transam.c routines,
* TransactionIdIsInProgress before TransactionIdDidCommit,
* because of race conditions explained in detail in tqual.c.
*/
if (TransactionIdIsCurrentTransactionId(xid) ||
@ -5646,46 +5642,40 @@ FreezeMultiXactId(MultiXactId multi, uint16 t_infomask,
Assert(!TransactionIdIsValid(update_xid));
update_xid = xid;
}
else if (!TransactionIdDidAbort(xid))
else if (TransactionIdDidCommit(xid))
{
/*
* Test whether to tell caller to set HEAP_XMAX_COMMITTED
* while we have the Xid still in cache. Note this can only
* be done if the transaction is known not running.
* The transaction committed, so we can tell caller to set
* HEAP_XMAX_COMMITTED. (We can only do this because we know
* the transaction is not running.)
*/
if (TransactionIdDidCommit(xid))
update_committed = true;
Assert(!TransactionIdIsValid(update_xid));
update_committed = true;
update_xid = xid;
}
/*
* Not in progress, not committed -- must be aborted or crashed;
* we can ignore it.
*/
/*
* Since the tuple wasn't marked HEAPTUPLE_DEAD by vacuum, the
* update Xid cannot possibly be older than the xid cutoff.
*/
Assert(!TransactionIdIsValid(update_xid) ||
!TransactionIdPrecedes(update_xid, cutoff_xid));
/*
* If we determined that it's an Xid corresponding to an update
* that must be retained, additionally add it to the list of
* members of the new Multis, in case we end up using that. (We
* members of the new Multi, in case we end up using that. (We
* might still decide to use only an update Xid and not a multi,
* but it's easier to maintain the list as we walk the old members
* list.)
*
* It is possible to end up with a very old updater Xid that
* crashed and thus did not mark itself as aborted in pg_clog.
* That would manifest as a pre-cutoff Xid. Make sure to ignore
* it.
*/
if (TransactionIdIsValid(update_xid))
{
if (!TransactionIdPrecedes(update_xid, cutoff_xid))
{
newmembers[nnewmembers++] = members[i];
}
else
{
/* cannot have committed: would be HEAPTUPLE_DEAD */
Assert(!TransactionIdDidCommit(update_xid));
update_xid = InvalidTransactionId;
update_committed = false;
}
}
newmembers[nnewmembers++] = members[i];
}
else
{