2-phase commit

Hi,

As the 7.4 beta rolls on, I thought now would be a good time to start
talking about the future.

I have a potential need in the future for distributed transactions
(XA). To get that from Postgres, I'd need two-phase commit, I think.
There is someone working on such a project
(<http://snaga.org/pgsql/>), but last time it was discussed here, it
received a rather lukewarm reception (see, e.g., the thread starting
at
<http://archives.postgresql.org/pgsql-hackers/2003-06/msg00752.php>).

While at OSCON, I had a discussion with Joe Conway, Bruce Momjian,
and Greg Sabino Mullane about 2PC. Various people expressed various
opinions on the topic, but I think we agreed on the following. The
relevant folks can correct me if I'm wrong:

Two-phase commit has theoretical problems, but it is implemented in
several "enterprise" RDBMS. 2PC is something needed by certain kinds
of clients (especially those with transaction managers), so if
PostgreSQL doesn't have it, PostgreSQL just won't get supported in
that arena. Someone is already working on 2PC, but may feel unwanted
due to the reactions last heard on the topic, and may not continue
working unless he gets some support. What is a necessary condition
for such support is to get some idea of what compromises 2PC might
impose, and thereafter to try to determine which such compromises, if
any, are acceptable ones.

I think the idea here is that, while in most cases a "pretty-good"
implementation of a desirable feature might get included in the
source on the grounds that it can always be improved upon later,
something like 2PC has the potential to do great harm to an otherwise
reliable transaction manager. So the arguments about what to do need
to be aired in advance.

I (perhaps foolishly) volunteered to undertake to collect the
arguments in various directions, on the grounds that I can contribute
no code, but have skin made of asbestos. I thought I'd try to
collect some information about what people think the problems and
potentially acceptable compromises are, to see if there is some way
to understand what can and cannot be contemplated for 2PC. I'll
include in any such outline the remarks found in the -hackers thread
referenced above. Any objections?

A

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Andrew Sullivan 204-4141 Yonge Street
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