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Subject: Re: data checksums
From: Christophe Pettus <xof@thebuild.com>
In-Reply-To: <830004cb0a514d803d13ab9abcfa15fbae365748.camel@cybertec.at>
Date: Tue, 6 Aug 2024 20:14:22 -0700
Cc: bruno vieira da silva <brunogiovs@gmail.com>,
 pgsql-general@lists.postgresql.org
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To: Laurenz Albe <laurenz.albe@cybertec.at>
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> On Aug 6, 2024, at 19:45, Laurenz Albe <laurenz.albe@cybertec.at> =
wrote:
> I am surprised by that.  Would you say that most storage systems will =
happily give you a
> garbage block if there was a hardware problem somewhere?

"Most" is hard for me to judge.  HDDs can have uncorrected and =
undetected errors, definitely.  ZFS, for example, can correct those =
(within limits); XFS doesn't try.  I have been told that SSDs can have =
uncorrected/undetected errors as well, but I don't know details on that.

> Turning data checksums on will write WAL for hint bits, which can =
significantly increase
> the amount of WAL written.

I was curious about that, so I just did a quick experiment using =
pgbench, with identical databases except for checksums.  They both =
generated the same amount of WAL within 10% or so, so I don't think the =
impact is huge.  (And you need the hint bits for pg_rewind, which is a =
nice thing to have in your back pocket if required.)=