| From: | Thomas Munro <thomas(dot)munro(at)gmail(dot)com> |
|---|---|
| To: | Dagfinn Ilmari Mannsåker <ilmari(at)ilmari(dot)org> |
| Cc: | Simon Riggs <simon(dot)riggs(at)enterprisedb(dot)com>, Julien Rouhaud <rjuju123(at)gmail(dot)com>, Ashutosh Sharma <ashu(dot)coek88(at)gmail(dot)com>, Daniel Gustafsson <daniel(at)yesql(dot)se>, Stephen Frost <sfrost(at)snowman(dot)net>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Andres Freund <andres(at)anarazel(dot)de>, David Steele <david(at)pgmasters(dot)net>, Dmitry Dolgov <9erthalion6(at)gmail(dot)com>, Jakub Wartak <Jakub(dot)Wartak(at)tomtom(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>, Tomas Vondra <tomas(dot)vondra(at)enterprisedb(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: WIP: WAL prefetch (another approach) |
| Date: | 2022-09-25 02:31:37 |
| Message-ID: | CA+hUKGLc+iOgkt1dT_h=mVzkupkMPzvER9HUa74oUFgCswJrSg@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Wed, Apr 13, 2022 at 8:05 AM Thomas Munro <thomas(dot)munro(at)gmail(dot)com> wrote:
> On Wed, Apr 13, 2022 at 3:57 AM Dagfinn Ilmari Mannsåker
> <ilmari(at)ilmari(dot)org> wrote:
> > Simon Riggs <simon(dot)riggs(at)enterprisedb(dot)com> writes:
> > > This is a nice feature if it is safe to turn off full_page_writes.
> > > When is it safe to do that? On which platform?
> > >
> > > I am not aware of any released software that allows full_page_writes
> > > to be safely disabled. Perhaps something has been released recently
> > > that allows this? I think we have substantial documentation about
> > > safety of other settings, so we should carefully document things here
> > > also.
> >
> > Our WAL reliability docs claim that ZFS is safe against torn pages:
> >
> > https://www.postgresql.org/docs/current/wal-reliability.html:
> >
> > If you have file-system software that prevents partial page writes
> > (e.g., ZFS), you can turn off this page imaging by turning off the
> > full_page_writes parameter.
>
> Unfortunately, posix_fadvise(WILLNEED) doesn't do anything on ZFS
> right now :-(.
Update: OpenZFS now has this working in its master branch (Linux only
for now), so fingers crossed for the next release.
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