From: | Justin Clift <justin(at)postgresql(dot)org> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | "Jeffrey W(dot) Baker" <jwbaker(at)acm(dot)org>, Postgres general mailing list <pgsql-general(at)postgresql(dot)org> |
Subject: | Re: Meaning of vacuum output |
Date: | 2002-01-17 02:47:26 |
Message-ID: | 3C463B3E.9ECFC71C@postgresql.org |
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Lists: | pgsql-general |
Tom Lane wrote:
>
> "Jeffrey W. Baker" <jwbaker(at)acm(dot)org> writes:
> > I shut down all connections, and vacuum has a different output:
>
> > NOTICE: Pages 33639: Changed 226, Empty 0; Tup 128819: Vac 2840812,
> > Keep 0, UnUsed 96275.
> > Total CPU 14.29s/28.69u sec elapsed 233.02 sec.
>
> Ah-hah, you did have open transactions.
>
> > So I conclude from these two data points that Keep means tuples that are
> > still visible to a transaction, Vac means tuples that are not visible to
> > any transaction. But, what is UnUsed?
>
> Looking at the code:
>
> Tup # tuples remaining after vacuum
> Vac # tuples removed by vacuum
> Keep # dead tuples kept because some xact can still see 'em
> Unused # unused item pointers
>
> "Keep" is included in the "Tup" total.
>
> The unused item pointers may get recycled later; it looks like that
> hasn't been determined yet at the point where these stats are printed.
I think this explanation would be worth mentioning in the documentation
for the VACUUM command (maybe as OUTPUT?).
???
Regards and best wishes,
Justin Clift
>
> regards, tom lane
>
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