Re: RE: [COMMITTERS] pgsql/src/backend/access/transam ( xact.c xlog.c)

Added to TODO:

* Delay fsync() when other backends are about to commit too

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> > > BUT, do we know for sure that sleep(0) is not optimized in
> > > the library to just return?
> >
> > We can only do our best here. I think guessing whether other backends
> > are _about_ to commit is pretty shaky, and sleeping every time is a
> > waste. This seems the cleanest.
>
> A long ago you, Bruce, made me gift - book about transaction processing
> (thanks again -:)). This sleeping before fsync in commit is described
> there as standard technique. And the reason is cleanest.
> Men, cost of fsync is very high! { write (64 bytes) + fsync() }
> takes ~ 1/50 sec. Yes, additional 1/200 sec or so results in worse
> performance when there is only one backend running but greatly
> increase overall performance for 100 simultaneous backends. Ie this
> delay is trade off to gain better scalability.
>
> I agreed that it must be configurable, smaller or probably 0 by
> default, use approximate # of simultaneously running backends for
> guessing (postmaster could maintain this number in shmem and
> backends could just read it without any locking - exact number is
> not required), good described as tuning patameter in documentation.
> Anyway I object sleep(0).
>
> Vadim
>

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