Re: Issues with Quorum Commit

Markus Wanner <markus(at)bluegap(dot)ch> writes:
> I don't buy that. The risk calculation gets a lot simpler and obvious
> with strict guarantees.

Ok, I'm lost in the use cases and analysis.

I still don't understand why you want to consider the system already
synchronous when it's not, whatever is the guarantee you're asking for.

All I'm saying is that we should be able to know and show what the
current system is up to, and we should be able to offer sane reactions
in case of errors.

You're calling a sane reaction blocking the master entirely when the
standby ain't ready yet (it's still at the base backup state), and I can
live with that. As an option.

I say that either we go the lax quorum route, or we have to care for
details and summary the failure cases with precision, and the possible
responses with care. I don't see that possible without a clear state of
each element in the system, their transitions, and a way to derive the
global state of the distributed system out of that.

It might be that the simpler way to go here is what Greg Smith has been
proposing for a long time already, and again quite recently on this
thread: have all the information you need in a system table and offer to
run a user defined function to determine the state of the system.

I think we managed to show what Josh Berkus wanted to know now. That's a
quagmire here. Now, the problem I have is not Quorum Commit but the very
definition of synchronous replication and the system we're trying to
build. Not sure there's two of us wanting the same thing here.

Regards,
--
Dimitri Fontaine
http://2ndQuadrant.fr PostgreSQL : Expertise, Formation et Support