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Re: Postgres XA support

From: Michael Allman <msa(at)allman(dot)ms>
To: Oliver Jowett <oliver(at)opencloud(dot)com>
Cc: Heikki Linnakangas <hlinnaka(at)iki(dot)fi>, pgsql-jdbc(at)postgresql(dot)org
Subject: Re: Postgres XA support
Date: 2005-08-16 03:06:38
Message-ID: 20050815225120.I62442@yvyyl (view raw, whole thread or download thread mbox)
Lists: pgsql-jdbc
On Tue, 16 Aug 2005, Oliver Jowett wrote:

> Michael Allman wrote:
>> Key to the protocol is the ability to start and end the association of
>> transactions to threads of control.  In particular, what's bothering me
>> is that there appears to be no way to end the transaction association of
>> the current postgres connection, either permanently or for suspension.
>> Please correct me if I'm wrong.
>> Thus work performed using the underlying physical connection of a
>> PGXAResource unassociated with any transaction will still be performed
>> on the connection's transaction.
> You'll need another layer to support all of XA's behaviour -- this was
> the discussion about mapping XA connections to physical connections that
> happened on the list a while back, wasn't it?
> It's probably unnecessary for the first cut, though. What exactly is the
> behaviour that you can't support without that extra layer, and is it
> needed for common use of XA? Seems to me that you could get away with
> just disallowing work on a Connection that has an unprepared XA
> transaction pending.

You can do something like that to flag unsupported behavior, but I think 
that without the ability to suspend and resume transaction branch 
association, the JDBC XA support will not graduate from "experimental" 
status.  I couldn't confidently recommend it for production use, and I 
wrote the damn thing.

I am pretty much decided that the JDBC XA support will require another 
approach.  If you really want to use my patchset, I will at least upload 
the latest version which includes some fixes and more verbose 
XAExceptions.  But I'm not sold on it myself anymore.

I think JDBC XA is going to require a lot more work.  The server-side 2PC 
support coming in postgres 8.1 is a good thing, but it's not XA.


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