Re: Sv: Re: Sv: Re: Sv: Re: Sv: Re: data-checksums

Hello,
A question seems to be, according to me, important :
How a corruption, detected thanks to data-checksums, is fixed?

Thank you,
Thomas

Le 10 janv. 2018 20:39, "Andres Freund" <andres(at)anarazel(dot)de> a écrit :

> On 2018-01-09 20:51:17 -0500, Stephen Frost wrote:
> > Greetings,
> >
> > * Andreas Joseph Krogh (andreas(at)visena(dot)com) wrote:
> > > Aha, so enabling CRC causes hint-bits to be written causing extra
> WAL-logging,
> > > which woudn't be the case without CRC enabled?
> > > Thanks for pointing that out.
> >
> > Yes, having checksums enabled forces logging of hint bits. You can
> > enable wal_log_hints independently too, without having checksums, to see
> > what kind of an impact it'll have on your environment.
> >
> > A useful documentation update might be:
> >
> > ---
> > With checksums enabled, wal_log_hints <link to the GUC's documentation>
> > will be enabled and each page read or write will involve calculating the
> > checksum for the page.
> > ---
> >
> > I'd probably just replace the "Enabling checksums may incur a noticeable
> > performance penalty" with the above, as it should be clear that doing
> > more work implies an impact on performance and that avoids the whole
> > question of trying to characterize in a general way something that can't
> > be generalized (as it's workload dependent).
>
> -1. I think this is underplaying the cost.
>
> Greetings,
>
> Andres Freund
>
>