On 19/08/10 04:46, Robert Haas wrote:
At any rate, we should definitely NOT wait another month to start thinking about Sync Rep again.
Agreed. EnterpriseDB is interested in having that feature, so I'm on the hook to spend time on it regardless of commitfests.
I haven't actually looked at any of the Sync Rep code AT ALL but IIRC Heikki expressed the view that the biggest thing standing in the way of a halfway decent Sync Rep implementation was a number of polling loops that needed to be replaced with something that wouldn't introduce up-to-100ms delays.
Well, that's the only uncontroversial thing about it that doesn't require any fighting over the UI or desired behavior. That's why I've focused on that first, and also because it's useful regardless of synchronous replication. But once that's done, we'll have to nail down how synchronous replication is supposed to behave, and how to configure it.
And so far we haven't seen a patch for that. Somebody write one. And then let's get it reviewed and committed RSN.
Fujii is on vacation, but I've started working on it. The two issues with Fujii's latest patch are that it would not respond promptly on platforms where signals don't interrupt sleep, and it suffers the classic race condition that pselect() was invented for. I'm going to replace pg_usleep() with select(), and use the so called "self-pipe trick" to get over the race condition. I have that written up but I want to do some testing and cleanup before posting the patch.
It may seem like we're early in the release cycle yet, but for a feature of this magnitude we are not. We committed way too much big stuff at the very end of the last release cycle; Hot Standby was still being cleaned up in May after commit in November. We'll be lucky to commit sync rep that early.
Agreed. We need to decide the scope and minimum set of features real soon to get something concrete finished.
BTW, on what platforms signals don't interrupt sleep? Although that issue has been discussed many times before, I couldn't find any reference to a real platform in the archives.
-- Heikki Linnakangas EnterpriseDB http://www.enterprisedb.com -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
