From: | Michael Paquier <michael(dot)paquier(at)gmail(dot)com> |
---|---|
To: | Mike Broers <mbroers(at)gmail(dot)com> |
Cc: | "pgsql-general(at)postgresql(dot)org" <pgsql-general(at)postgresql(dot)org> |
Subject: | Re: question about checksum in 9.3 |
Date: | 2014-01-14 01:11:11 |
Message-ID: | CAB7nPqR+zu6zbu1jAJeRx6OZ3nfxvPJrya3+ogz1EMBQtwvd7g@mail.gmail.com |
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Lists: | pgsql-general |
On Tue, Jan 14, 2014 at 1:50 AM, Mike Broers <mbroers(at)gmail(dot)com> wrote:
> Hello, I am in the process of planning a 9.3 migration of postgres and I am
> curious about the checksum features available. In my test 9.3 instance it
> seemed like this feature provides a log entry of the exact database/oid of
> the corrupt object when it is accessed, but not much else. I can't find
> much documentation on anything else this feature provides.
Few things:
- The only way to know if a server is using data checksums is to use
pg_controldata.
- Be aware as well of the potential performance impact on your CPU,
checksums are checked each time a page is read, and recalculated each
time a page is updated.
- ignore_checksum_failure can be used to ignore failures. Don't use
that on a production system.
> Is there a built-in method of scanning the server to check for corruption or
> will I have to wait for a corrupt object to be accessed to see the log
> entry?
You can as well access manually tables with some for example
sequential scan to check if blocks are broken or not.
> Is there a relation that stores last checksum status or anyway of
> reporting on what objects are identified by postgres as corrupt or not
> corrupt?
No, you could build one though with a background worker that scans
relation pages and registers that failing blocks.
> Are there any other features of the checksum I am missing besides the log
> entry?
9.4 has a new GUC parameter called data_checksums that allow you to
check with a psql client if checksums are used on a server.
Regards,
--
Michael
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