Re: Read-only access to temp tables for 2PC transactions

On Thu, May 23, 2019 at 08:54:59AM -0700, Andres Freund wrote:
> On 2019-05-23 12:36:09 +0100, Simon Riggs wrote:
>> The ONLY case where this matters is if someone does a PREPARE and then
>> starts doing other work on the session. Which makes no sense in the normal
>> workflow of a session. I'm sure there are tests that do that, but those
>> tests are unrepresentative of sensible usage.
>
> That's extremely common.
>
> There's no way we can forbid using session after 2PC unconditionally,
> it'd break most users of 2PC.

This does not break Postgres-XC or XL as their inner parts with a
COMMIT involving multiple write nodes issue a set of PREPARE
TRANSACTION followed by an immediate COMMIT PREPARED which are
transparent for the user, so the point of Simon looks sensible from
this angle. Howewer, I much agree with Andres that it is very common
to have PREPARE and COMMIT PREPARED issued with different sessions. I
am not much into the details of XA-compliant drivers, but I think that
having us lose this property would be the source of many complaints.
--
Michael