| From: | Simon Riggs <simon(dot)riggs(at)enterprisedb(dot)com> |
|---|---|
| To: | Tomas Vondra <tomas(dot)vondra(at)enterprisedb(dot)com> |
| Cc: | Thomas Munro <thomas(dot)munro(at)gmail(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>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: WIP: WAL prefetch (another approach) |
| Date: | 2022-04-12 15:46:39 |
| Message-ID: | CANbhV-EVrOSZqk0MofgZa1xqNmFgXwFaC6JyvBfDR+stqzAfLQ@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Tue, 12 Apr 2022 at 16:41, Tomas Vondra
<tomas(dot)vondra(at)enterprisedb(dot)com> wrote:
>
> On 4/12/22 15:58, Simon Riggs wrote:
> > On Thu, 7 Apr 2022 at 08:46, Thomas Munro <thomas(dot)munro(at)gmail(dot)com> wrote:
> >
> >> With that... I've finally pushed the 0002 patch and will be watching
> >> the build farm.
> >
> > 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.
> >
>
> I don't see why/how would an async prefetch make FPW unnecessary. Did
> anyone claim that be the case?
Other way around. FPWs make prefetch unnecessary.
Therefore you would only want prefetch with FPW=off, AFAIK.
Or put this another way: when is it safe and sensible to use
recovery_prefetch != off?
--
Simon Riggs http://www.EnterpriseDB.com/
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