Re: VACUUM FULL

On Sat, 11 May 2002, Tom Lane wrote:

>
> Brian McCane <bmccane(at)mccons(dot)net> writes:
> > It appeared while the VACUUM FULL was occurring, that the index files were
> > sort of rewritten in place.
>
> No, it just has to make new index entries for the rows it moves. It
> seems highly unlikely to me that this would somehow improve the index
> structure substantially. Puzzling...
>
> regards, tom lane
>

This is what I thought that it was doing to the indexes as well. I
believe, but I am not sure because I didn't record an 'ls -l' of all the
tables involved, that my datafile shrunk about 2x the freed space that I
got back (ie. about 2 less 1GB files). I guess this could be from the
rewritten index information possibly growing the actual index files a
little? Would I possibly see another performance boost if I rebuilt the
indexes involved like I used to in 7.1.3? I still have the Perl script
sitting around here some place, but assumed from things said by you and
Bruce in the past few months about 7.2.x that it wouldn't be necessary
anymore. I guess I'll give it a try this weekend and see what happens.

Also, I disabled my nightly VACUUM ANALYZE from cron while I was doing
this because I was unsure what would happen with multiple VACUUM's
running. And looking back at the command that I ran, it was only a
"VACUUM FULL foo". This would mean that no statistics were updated,
right? If so, all of my post-vacuum testing has been with pre-vacuum
stats. Just to be sure, (and because I just realized I had forgot), I
re-enabled the VACUUM ANALYZE and checked my stats. They are nearly
identical.

stranger and stranger ;)
- brian

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