| From: | Dan Ports <drkp(at)csail(dot)mit(dot)edu> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>, Kevin Grittner <Kevin(dot)Grittner(at)wicourts(dot)gov>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: SSI atomic commit |
| Date: | 2011-07-07 21:08:07 |
| Message-ID: | 20110707210807.GE76634@csail.mit.edu |
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| Lists: | pgsql-hackers |
On Thu, Jul 07, 2011 at 04:48:55PM -0400, Tom Lane wrote:
> Seems to me there's a more fundamental reason not to do that, which is
> that once you've done PREPARE it is no longer legitimate to decide to
> roll back the transaction to get out of a "dangerous" structure --- ie,
> you have to target one of the other xacts involved instead. Shouldn't
> the assignment of a prepareSeqNo correspond to the point where the xact
> is no longer a target for SSI rollback?
That part is already accomplished by setting SXACT_FLAG_PREPARED (and
choosing a new victim if we think we want to abort a transaction with
that flag set).
prepareSeqNo is being used as a lower bound on the transaction's commit
sequence number. It's currently set at the same time as the PREPARED
flag, but it doesn't have to be.
Dan
--
Dan R. K. Ports MIT CSAIL http://drkp.net/
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