Re: Disk Utilization Increases And Time for Vacuum Increases.

From: Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>
To: Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, "scott(dot)marlowe" <scott(dot)marlowe(at)ihs(dot)com>, Jeff Boes <jboes(at)qtm(dot)net>, pgsql-admin(at)postgresql(dot)org
Subject: Re: Disk Utilization Increases And Time for Vacuum Increases.
Date: 2003-09-05 04:32:17
Message-ID: 200309050432.h854WHZ03541@candle.pha.pa.us
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I have looked at the code and it seems VACUUM FULL does collect index
free space into the FSM via index_vacuum_cleanup(). Is that true?

---------------------------------------------------------------------------

Bruce Momjian wrote:
> Bruce Momjian wrote:
> > > > AFAIK, VACUUM doesn't reclaim space taken up by indexes. In fact, the more
> > > > deletes you do, the larger the index space gets, and the *slower* the index
> > > > performs. A periodic REINDEX cleans up a lot of problems.
> > >
> > > Note that in 7.4 the fix for this is in, so if you have a chance to test
> > > it out with your indexes and their growth problem please test it to see if
> > > it works right.
> > >
> > > I haven't tested 7.4 beta1 yet very hard, just on my workstation, with
> > > relatively low level stuff.
> >
> > I am not sure we have completely dealt with index growth in 7.4. What
> > we have new in 7.4 is the ability for non-FULL VACUUM to collect info on
> > free index pages and reuse them.
> >
> > However, VACUUM FULL does not shrink the index table unless those pages
> > are the last pages of the file. (Could it shift free pages to the end
> > and then truncate index?) Also, does VACUUM FULL on an index put the
> > empty index pages in the FSM map? It doesn't do that for heap pages
> > because there are none after vacuum, but there might be free index pages
> > that we should record.
>
> I haven't seen anyone comment on this. I think we need to address this
> for 7.4. (Collecting index free space in FSM is new in 7.4.) I am
> concerned that people who are only running VACUUM FULL at night will
> have problems with index growth. Also, why can't we move totally-empty
> index pages to the end and truncate the file?
>
> > Interesting I found a reference of doing an auto-reindex as part of
> > VACUUM FULL:
> >
> > #ifdef NOT_USED
> >
> > /*
> > * reindex in VACUUM is dangerous under WAL. ifdef out until it
> > * becomes safe.
> > */
> > if (reindex)
> > {
> > vac_close_indexes(nindexes, Irel);
> > Irel = (Relation *) NULL;
> > activate_indexes_of_a_table(onerel, false);
> > }
> > #endif /* NOT_USED */
>
> Will we ever reindex as part of VACUUM FULL?
>
> --
> Bruce Momjian | http://candle.pha.pa.us
> pgman(at)candle(dot)pha(dot)pa(dot)us | (610) 359-1001
> + If your life is a hard drive, | 13 Roberts Road
> + Christ can be your backup. | Newtown Square, Pennsylvania 19073
>
> ---------------------------(end of broadcast)---------------------------
> TIP 8: explain analyze is your friend
>

--
Bruce Momjian | http://candle.pha.pa.us
pgman(at)candle(dot)pha(dot)pa(dot)us | (610) 359-1001
+ If your life is a hard drive, | 13 Roberts Road
+ Christ can be your backup. | Newtown Square, Pennsylvania 19073

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