Re: Re[6]: [Firebird-devel] Max transaction duration

[Ann W. H. <aha...@ib...>]

At 09:32 PM 12/15/2002 +0100, Pavel Cisar wrote:
> >
> > I believe that client death does establish an OIT.
>
>But when client dies and server notice, server performs the rollback,
>don't he ?

The server changes the state of the transaction to rolled back,
but the undo log is not available (or reliable) so the transaction
can affect the OIT>

> > Actually it requires both a backup and a restore.  Gbak doesn't do the
> > bookkeeping necessary to notice what transactions it has undone.  Only
> > sweep does that.
>
>But when sweep is performed on backup ? I would suppose that restore is
>not necessary then.

Sweep is a different operation than backup.  Sweep moves the OIT, backup
alone does not.  Backup and restore does, of course, by recreating the
database with all new transaction id's.

>So you say that GC can expunge rolled back versions beyond OAT, leaving
>there just those that are not removable (i.e. limbo) ?

Yes.  Unneeded record versions older than the OIT can be garbage collected.
Limbo transactions don't count as unneeded.


>But I meant read-only (by definition in trn parameter block) read
>committed transactions you mentioned earlier. They internally acquire pre-
>committed status, don't they ?

yes.


>I see. That would really make a difference. But does this really need a
>bookkeeping ? How about an extension logic in VIO_chase_record_version
>that will notice subsequent versions from committed transactions and mark
>it for GC (and extended GC to handle that, of course) ?

The problem, and the reason for the bookkeeping, is that we currently
keep track of the oldest active.  That's an over-simplification.  The
"oldest active" is actually the oldest transaction that was active
when any currently active transaction started.  In order to remove
intermediate versions, we'd need to keep track of the oldest transaction
that was active when each active transaction started.  There's also
the problem of reconstructing back versions from differences, but that's
not so difficult.



Regards,

Ann
www.ibphoenix.com
We have answers.