Re: Two-phase commit

On Sun, 8 Feb 2004, Jeroen T. Vermeulen wrote:

> On Wed, Feb 04, 2004 at 10:22:16PM +0200, Heikki Linnakangas wrote:
>
> > There is a system view pg_prepared_xacts that gives you all transactions
> > that are in prepared state waiting for COMMITPREPARED or ABORTPREPARED.
>
> Great to hear that you've gotten so far with this... One question: can I
> check for this view to see if 2PC is supported before issuing the new
> kind of commit? I'm interested in supporting 2PC even for some regular
> transactions to reduce their in-doubt window, but I don't want to issue a
> command at the last moment that may fail (and thereby abort) because the
> backend version I'm connected to doesn't support the new command!

Yes, I suppose that would work. Though you would have to use a query that
wouldn't fail in case the view doesn't exist, otherwise you end up
aborting the transaction anyway. This should work:

SELECT COUNT(*) FROM pg_views WHERE schemanem='pg_catalog' AND viewname
='pg_prepared_xacts'

If it returns 1, you can do 2PC, if it returns 0, you have to regular
commit.

However, if this gets into 7.5, I guess you could just check for the
version of the backend instead with "SELECT version()".

- Heikki