Re: patch to allow disable of WAL recycling

On Tue, Jul 17, 2018 at 4:47 PM, Tomas Vondra
<tomas(dot)vondra(at)2ndquadrant(dot)com> wrote:
> Makes sense, I guess. But I think many claims made in this thread are
> mostly just assumptions at this point, based on our beliefs how CoW or
> non-CoW filesystems work. The results from ZFS (showing positive impact)
> are an exception, but that's about it. I'm sure those claims are based
> on real-world experience and are likely true, but it'd be good to have
> data from a wider range of filesystems / configurations etc. so that we
> can give better recommendations to users, for example.

I agree that there's a lot of assuming going on.

> That's something I can help with, assuming we agree on what tests we
> want to do. I'd say the usual batter of write-only pgbench tests with
> different scales (fits into s_b, fits into RAM, larger then RAM) on
> common Linux filesystems (ext4, xfs, btrfs) and zfsonlinux, and
> different types of storage would be enough. I don't have any freebsd box
> available, unfortunately.

Those sound like reasonable tests. I also don't think we need to have
perfect recommendations. Some general guidance is good enough for a
start and we can refine it as we know more. IMHO, anyway.

--
Robert Haas
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