Обсуждение: Two Phase Commit support
Hello all, Is it correct that postgresql can not support two phase commits? If not is there any plans to do so? We are doing a large amount of development on EJB servers and need to perform two phase commits between the database server and the mom server. Regards, Stephen.
I'm not sure of the functionality your looking for, can you point me to a definition of "two phased commits"? Robert Treat On Sat, 2002-10-26 at 06:53, Stephen J. Thompson wrote: > Hello all, > > Is it correct that postgresql can not support two phase commits? If not is > there any plans to do so? We are doing a large amount of development on EJB > servers and need to perform two phase commits between the database server and > the mom server. > > Regards, > > Stephen. > > > ---------------------------(end of broadcast)--------------------------- > TIP 6: Have you searched our list archives? > > http://archives.postgresql.org
Robert Treat wrote: > I'm not sure of the functionality your looking for, can you point me to > a definition of "two phased commits"? > > Robert Treat He's probably updating/inserting data on many pgsql servers at once, two-phase commits are the best-known algorithm to do it safely: Phase 1: Perform queries on all servers, commit -- wait for commit confirmation from all servers Phase 2: If there have not been any errors, perform the "real" commit on all servers; else perform a rollback and undo changes. The commit from phase 1 isn't a real commit, although data is written to disk, etc, the database still waits for the second commit to make the changes visible. I don't think there's any way to do it in Pgsql. Once you committed the data the first time, the only way to undo the changes is to send a batch of queries to reverse them. Cristóvão > > > On Sat, 2002-10-26 at 06:53, Stephen J. Thompson wrote: > > >Hello all, > > > >Is it correct that postgresql can not support two phase commits? If > not is > >there any plans to do so? We are doing a large amount of development > on EJB > >servers and need to perform two phase commits between the database > server and > >the mom server. > > > >Regards, > > > >Stephen.
I agree with Cristóvão. Also, two-phase commit only makes sense in the
context of multiple database servers which are replicating to each other in
real time. Once postgresql has replication in place then they should
probably start considering two-phase commit; unless they decide to roll out
both at once of course. ;-)
I continue to be impressed with the progress of the postgresql development
team, and how stable the released versions are. Keep up the good work!
Wes Sheldahl
Cristóvão Dalla Costa <cbraga@bsi.com.br>@postgresql.org on 10/28/2002
06:02:24 PM
Sent by: pgsql-general-owner@postgresql.org
To: Robert Treat <xzilla@users.sourceforge.net>
cc: stephen@cass-ltd.co.uk, "pgsql-general@postgresql.org"
<pgsql-general@postgresql.org>
Subject: Re: [GENERAL] Two Phase Commit support
Robert Treat wrote:
> I'm not sure of the functionality your looking for, can you point me to
> a definition of "two phased commits"?
>
> Robert Treat
He's probably updating/inserting data on many pgsql servers at once,
two-phase commits are the best-known algorithm to do it safely:
<details snipped>
I don't think there's any way to do it in Pgsql. Once you committed the
data the first time, the only way to undo the changes is to send a batch
of queries to reverse them.
Cristóvão
>
>
> On Sat, 2002-10-26 at 06:53, Stephen J. Thompson wrote:
>
> >Hello all,
> >
> >Is it correct that postgresql can not support two phase commits? If
> not is
> >there any plans to do so? We are doing a large amount of development
> on EJB
> >servers and need to perform two phase commits between the database
> server and
> >the mom server.
> >
> >Regards,
> >
> >Stephen.
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I thought databases that support begin-end transactions use "two phase commit" or some derivative of it to achieve such operations. Two Phase Commit is a technology used in distributed applications, to assure that both parties (client and server) are understanding each other and no ambiguity about what just took place exists. Robert Treat wrote: >I'm not sure of the functionality your looking for, can you point me to >a definition of "two phased commits"? > >Robert Treat > >On Sat, 2002-10-26 at 06:53, Stephen J. Thompson wrote: > > >>Hello all, >> >>Is it correct that postgresql can not support two phase commits? If not is >>there any plans to do so? We are doing a large amount of development on EJB >>servers and need to perform two phase commits between the database server and >>the mom server. >> >>Regards, >> >>Stephen. >> >> >>---------------------------(end of broadcast)--------------------------- >>TIP 6: Have you searched our list archives? >> >>http://archives.postgresql.org >> >> > > > > >---------------------------(end of broadcast)--------------------------- >TIP 6: Have you searched our list archives? > >http://archives.postgresql.org > >
wsheldah@lexmark.com writes: > I agree with Cristóvão. Also, two-phase commit only makes sense in the > context of multiple database servers which are replicating to each other in > real time. Once postgresql has replication in place then they should > probably start considering two-phase commit; unless they decide to roll out > both at once of course. ;-) The Pgreplication project is in the process of implementing a new eager, multi-master replication design that should be a lot more scalable than 2PC -- see here for more info: http://citeseer.nj.nec.com/330257.html BTW, the Pgreplication homepage is here: http://gborg.postgresql.org/project/pgreplication/projdisplay.php Cheers, Neil -- Neil Conway <neilc@samurai.com> || PGP Key ID: DB3C29FC