Re: Possible documentation error

OK, wording updated. Thanks.

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

Jim C. Nasby wrote:
> On Tue, Dec 26, 2006 at 07:22:21PM +0100, Martijn van Oosterhout wrote:
> > On Tue, Dec 26, 2006 at 12:49:55PM -0500, D'Arcy J.M. Cain wrote:
> > > On Tue, 26 Dec 2006 18:12:45 +0100
> > > Martijn van Oosterhout <kleptog(at)svana(dot)org> wrote:
> > > > On Tue, Dec 26, 2006 at 12:04:40PM -0500, D'Arcy J.M. Cain wrote:
> > > > > Now it certainly seems to me that it should behave as described given
> > > > > the definition of VACUUM FULL so I am a little confused by my tests.
> > > > > My test table only has two entries in it. Is that the issue? In fact,
> > > > > I find the same behaviour if I do a simple VACUUM on the table.
> > > >
> > > > On a table with two entries, VACUUM FULL is going to do nothing of
> > > > interest. Moving tuples within a page is useless, generally.
> > >
> > > I thought that that might be the issue. The docs should probably say
> > > "can" instead of "will" then.
> >
> > The doumenttion is accurate as is. It says when "moved by VACUUM FULL".
> > In your case they wern't moved. If you change the word "will" to "can",
> > it will be wrong.
>
> Howso? There's no guarantee (which is what "will" implies) that a ctid
> will change on VACUUM FULL. In fact, your example demonstrates that; 0,1
> stayed put.
>
> I'm sorry if it sounds like I'm picking nits, but using CTID to
> identify rows could provide a noticeable performance gain in some cases.
> But users can't make use of that if it's not clear exactly when and how
> CTIDs can change.
> --
> Jim Nasby jim(at)nasby(dot)net
> EnterpriseDB http://enterprisedb.com 512.569.9461 (cell)
>
> ---------------------------(end of broadcast)---------------------------
> TIP 5: don't forget to increase your free space map settings

--
Bruce Momjian bruce(at)momjian(dot)us
EnterpriseDB http://www.enterprisedb.com

+ If your life is a hard drive, Christ can be your backup. +