| From: | Julien Rouhaud <rjuju123(at)gmail(dot)com> |
|---|---|
| To: | Andres Freund <andres(at)anarazel(dot)de> |
| Cc: | Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Michael Banck <michael(dot)banck(at)credativ(dot)de>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
| Subject: | Re: Online verification of checksums |
| Date: | 2019-03-08 15:19:03 |
| Message-ID: | CAOBaU_ZaC3PSm50Dih8w0AiyUNd+GbP3M90RR3LstVbr1jOdgQ@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Thu, Mar 7, 2019 at 7:00 PM Andres Freund <andres(at)anarazel(dot)de> wrote:
>
> On 2019-03-07 12:53:30 +0100, Tomas Vondra wrote:
> >
> > But then again, we could just
> > hack a special version of ReadBuffer_common() which would just
>
> > (a) check if a page is in shared buffers, and if it is then consider the
> > checksum correct (because in memory it may be stale, and it was read
> > successfully so it was OK at that moment)
> >
> > (b) if it's not in shared buffers already, try reading it and verify the
> > checksum, and then just evict it right away (not to spoil sb)
>
> This'd also make sense and make the whole process more efficient. OTOH,
> it might actually be worthwhile to check the on-disk page even if
> there's in-memory state. Unless IO is in progress the on-disk page
> always should be valid.
Definitely. I already saw servers with all-frozen-read-only blocks
popular enough to never get evicted in months, and then a minor
upgrade / restart having catastrophic consequences.
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