From: | Michael Paquier <michael(at)paquier(dot)xyz> |
---|---|
To: | Magnus Hagander <magnus(at)hagander(dot)net> |
Cc: | "Drouvot, Bertrand" <bertranddrouvot(dot)pg(at)gmail(dot)com>, Julien Rouhaud <rjuju123(at)gmail(dot)com>, David Steele <david(at)pgmasters(dot)net>, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Checksum errors in pg_stat_database |
Date: | 2022-12-11 23:40:04 |
Message-ID: | Y5ZqVOTgxsHVzoWJ@paquier.xyz |
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Lists: | pgsql-hackers |
On Sun, Dec 11, 2022 at 09:18:42PM +0100, Magnus Hagander wrote:
> It would be less of a concern yes, but I think it still would be a concern.
> If you have a large amount of corruption you could quickly get to millions
> of rows to keep track of which would definitely be a problem in shared
> memory as well, wouldn't it?
Yes. I have discussed this item with Bertrand off-list and I share
the same concern. This would lead to an lot of extra workload on a
large seqscan for a corrupted relation when the stats are written
(shutdown delay) while bloating shared memory with potentially
millions of items even if variable lists are handled through a dshash
and DSM.
> But perhaps we could keep a list of "the last 100 checksum failures" or
> something like that?
Applying a threshold is one solution. Now, a second thing I have seen
in the past is that some disk partitions were busted but not others,
and the current database-level counters are not enough to make a
difference when it comes to grab patterns in this area. A list of the
last N failures may be able to show some pattern, but that would be
like analyzing things with a lot of noise without a clear conclusion.
Anyway, the workload caused by the threshold number had better be
measured before being decided (large set of relation files with a full
range of blocks corrupted, much better if these are in the OS cache
when scanned), which does not change the need of a benchmark.
What about just adding a counter tracking the number of checksum
failures for relfilenodes in a new structure related to them (note
that I did not write PgStat_StatTabEntry)?
If we do that, it is then possible to cross-check the failures with
tablespaces, which would point to disk areas that are more sensitive
to corruption.
--
Michael
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