i'm not suggesting that Postgres should necessarily be able to repair a
corruption in the WAL, my issue is that there is no way of knowing that there
was a corruption in the WAL because the normal detection of the end of the WAL
is reported the same way as a corruption in the middle of the WAL.
i'd like some unequivocal indication that the WAL was corrupted.
thanks.
From: Jeff Davis pg...@j-davis.com
To: Jameison Martin jameis...@yahoo.com
Cc: pgsql-general@postgresql.org pgsql-general@postgresql.org
Sent: Wednesday, March 14, 2012 3:55 PM
Subject: Re: [GENERAL] xlog corruption
On Mon, 2012-02-27 at 16:30 -0800, Jameison Martin wrote:
I'd like to get some clarification around an architectural point about
recovery. I see that it is normal to see unexpected pageaddr errors
during recovery because of the way Postgres overwrites old log files,
and thus this is taken to be a normal termination condition, i.e. the
end of the log (see
http://doxygen.postgresql.org/xlog_8c.html#a0519e464bfaa79bde3e241e6cff986c7).
My question is how does recovery distinguish between the actual end of the
log as opposed to a log file corruption (e.g. torn page)?
I'd like to be able to distinguish between a corruption in the log vs.
a normal recovery condition if possible.
If you have a power failure, a torn page in the WAL is expected. Torn
pages in the data pages are fixed up using WAL; but WAL doesn't have
anything under it to prevent/fix torn pages (unless your filesystem
prevents them).
Of course, checksums are used to prevent recovery from attempting to
play a partial or otherwise corrupt WAL record.
What kind of corruption are you trying to detect?
Regards,
Jeff Davis
