Re: [PATCHES] Cleaning up unreferenced table files - Mailing list pgsql-hackers

From Bruce Momjian
Subject Re: [PATCHES] Cleaning up unreferenced table files
Date
Msg-id 200505111319.j4BDJvH04879@candle.pha.pa.us
Whole thread Raw
In response to Re: [PATCHES] Cleaning up unreferenced table files  (Tom Lane <tgl@sss.pgh.pa.us>)
List pgsql-hackers
Tom Lane wrote:
> Heikki Linnakangas <hlinnaka@iki.fi> writes:
> > On Tue, 10 May 2005, Bruce Momjian wrote:
> >> The current code is nice and localized and doesn't add any burden on our
> >> existing code, which is already complicated enough.  I think we either
> >> fix checkfiles.c, or we remove it and decide it isn't worth checking for
> >> unrefrenced files.
> 
> > Let's pull the patch for now.
> 
> FWIW, I was OK with the idea of adding something similar to the given
> patch to find out whether we had a problem or not.  With sufficient
> evidence that lost files are a big problem, I'd be in favor of a
> mechanism of the kind proposed in Heikki's latest messages.  The
> disconnect for me at the moment is that there's no evidence to justify
> that amount of effort/risk.  A startup-time patch would have provided
> that evidence, or else have proven that it's not worth spending more
> time on.

Agreed.  Imagine a backend creates a table file, then the operating
system crashes.  I assume WAL wasn't fsync'ed, so there is no way that
WAL can discover that unreferenced file.  

While I think WAL can correct some cases, I don't think it can correct
them all, so it seems it is necessary to check the file system against
pg_class to catch all the cases.  The transaction and file system
semantics are just different and need to be checked against each other.

--  Bruce Momjian                        |  http://candle.pha.pa.us pgman@candle.pha.pa.us               |  (610)
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