Re: Experimental patch for inter-page delay in VACUUM

Jan Wieck wrote:
> >> > If the background cleaner has to not just write() but write/fsync or
> >> > write/O_SYNC, it isn't going to be able to clean them fast enough. It
> >> > creates a bottleneck where we didn't have one before.
> >> >
> >> > We are trying to eliminate an I/O storm during checkpoint, but the
> >> > solutions seem to be making the non-checkpoint times slower.
> >> >
> >>
> >> It looks as if you're assuming that I am making the backends unable to
> >> write on their own, so that they have to wait on the checkpointer. I
> >> never said that.
> >
> > Maybe I missed it but are those backend now doing write or write/fsync?
> > If the former, that is fine. If the later, it does seem slower than it
> > used to be.
>
> In my all_performance.v4.diff they do write and the checkpointer does
> write+sync.

Again, sorry to be confusing --- I might be good to try write/fsync from
the background writer if backends can do writes on their own too without
fsync. The additional fsync from the background writer should reduce
disk writing during sync(). (The fsync should happen with the buffer
unlocked.)

You stated you didn't see improvement when the background writer did
non-checkpoint writes unless you modified update(4). Adding fsync might
correct that.

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