Re: Can PostgreSQL create new WAL files instead of reusing old ones?

Thomas,

Thanks for taking a look at this. I'll work on getting a patch together for
the master branch. I'll also take a look at the other question you raised
and get back to you once I have more information.

Thanks again,
Jerry

On Thu, Jun 21, 2018 at 10:20 PM, Thomas Munro <
thomas(dot)munro(at)enterprisedb(dot)com> wrote:

> On Fri, Jun 22, 2018 at 11:22 AM, David Pacheco <dap(at)joyent(dot)com> wrote:
> > On Wed, Jun 20, 2018 at 10:35 AM, Jerry Jelinek <
> jerry(dot)jelinek(at)joyent(dot)com>
> > wrote:
> >> I have implemented a small change to allow WAL recycling to be disabled.
> >> It is visible at:
> >> https://cr.joyent.us/#/c/4263/
> >>
> >> I'd appreciate getting any feedback on this.
>
> >> tl;dr: We've found that under many conditions, PostgreSQL's re-use of
> old
> >> WAL files appears to significantly degrade query latency on ZFS.
>
> I haven't tested by it looks reasonable to me. It needs documentation
> in doc/src/sgml/config.sgml. It should be listed in
> src/backend/utils/misc/postgresql.conf.sample. We'd want a patch
> against our master branch. Could you please register it in
> commitfest.postgresql.org so we don't lose track of it?
>
> Hey, a question about PostgreSQL on ZFS: what do you guys think about
> pg_flush_data() in fd.c? It does mmap(), msync(), munmap() to try to
> influence writeback? I wonder if at least on some operating systems
> that schlepps a bunch of data out of ZFS ARC into OS page cache, kinda
> trashing the latter?
>
> --
> Thomas Munro
> http://www.enterprisedb.com
>