Re: Replication Ideas - Mailing list pgsql-general

On Sat, 2003-08-23 at 23:27, Chris Travers wrote:
> Hi--
>
> I had been thinking of the issues of multimaster replication and how to
> do highly available, loadballanced clustering with PostgreSQL.  Here is
> my outline, and I am looking for comments on the limitations of how this
> would work.
>
> Several PostgreSQL servers would share a virtual IP address, and would
> coordinate among themselves which will act as "Master" for the purposes
> of a single transaction (but connection could be easier).  SELECT
> statements are handled exclusively by the transaction master while
> anything that writes to a database would be sent to all the the
> "Masters."  At the end of each transaction the systems would poll
> eachother regarding whether they were all successful:
>
> 1:  Any system which is successful in COMMITting the transaction must
> ignore any system which fails the transaction untill a recovery can be made.
>
> 2:  Any system which fails in COMMITting the transaction must cease to
> be a master, provided that it recieves a signat from any other member of
> the cluster that indicates that that member succeeded in committing the
> transaction.
>
> 3: If all nodes fail to commit, then they all remain masters.
>
> Recovery would be done in several steps:
>
> 1:  The database would be copied to the failed system using pg_dump.
> 2:  A current recovery would be done from the transaction log.
> 3:  This would be repeated in order to ensure that the database is up to
> date.
> 4:  When two successive restores have been achieved with no new
> additions to the database, the "All Recovered" signal is sent to the
> cluster and the node is ready to start processing again. (need a better
> way of doing this).
>
> Note:  Recovery is the problem, I know.  my model is only a starting
> point for the purposes of discussion and trying to bring something to
> the conversation.

This is vaguely similar to Two Phase Commit, which is a sine qua
non of distributed transactions, which is the s.q.n. of multi-master
replication.

--
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Ron Johnson, Jr. ron.l.johnson@cox.net
Jefferson, LA USA

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