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
