Re: VACUUM touching file but not updating relation

On 14 October 2011 12:12, Thom Brown <thom(at)linux(dot)com> wrote:
> Hi,
>
> I just noticed that the VACUUM process touches a lot of relations
> (affects mtime) but for one file I looked at, it didn't change.  This
> doesn't always happen, and many relations aren't touched at all.
>
> I had the following relation:
>
> -rw-------  1 thom  staff      40960 13 Oct 16:06 11946
>
> Ran MD5 over the file:
>
> MD5 (11946) = d6626f930f1fb6d77c3907d3279fe693
>
> Then VACUUM ANALYSE'd all databases in full.
>
> This relation was supposedly affected:
>
> -rw-------  1 thom  staff      40960 14 Oct 11:27 11946
>
> But then I ran MD5 back over it:
>
> MD5 (11946) = d6626f930f1fb6d77c3907d3279fe693
>
> This is the same as before.  What is it doing?  Does this happen
> often?  And I can't find out what this particular OID relates to
> either.
>
> I'm using 9.2devel btw.

Does anyone know what happened here? I'm just wondering if there's
some action being performed on the file which can be avoided. Of
course I haven't determined how often this happens.

--
Thom Brown
Twitter: @darkixion
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Registered Linux user: #516935

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