Re: [PATCH] 2PC state files on shared memory

Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> writes:
> Tom Lane wrote:
>> What if PREPARE simply didn't write the 2PC file at all, except into WAL?

> Interesting idea, might be worth performance testing. Peeking into the
> WAL files during normal operation feels naughty, but it should work.
> However, if the bottleneck is the WAL fsyncs, I doubt it's any faster
> than Michael's current patch.

This isn't about faster, it's about not requiring users to estimate
a suitable size for a shared-memory arena.

> Actually, it would be interesting to performance test a stripped down
> broken implementation that doesn't write the state files anywhere but
> WAL, PREPARE releases all locks like regular COMMIT does, and COMMIT
> PREPARED just writes the commit record and fsyncs. That would give an
> upper bound on how much gain any of these patches can have. If that's
> not much, we can throw in the towel.

Good idea --- although I would think that the performance of 2PC would
be pretty context-dependent anyway. What load would you test under?

regards, tom lane