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Re: Sort time

From: pginfo <pginfo(at)t1(dot)unisoftbg(dot)com>
To: Stephan Szabo <sszabo(at)megazone23(dot)bigpanda(dot)com>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, josh(at)agliodbs(dot)com,Rod Taylor <rbt(at)rbt(dot)ca>, "scott(dot)marlowe" <scott(dot)marlowe(at)ihs(dot)com>,"pgsql-performance(at)postgresql(dot)org" <pgsql-performance(at)postgresql(dot)org>
Subject: Re: Sort time
Date: 2002-11-17 06:30:28
Message-ID: 3DD73784.11ED2512@t1.unisoftbg.com (view raw or flat)
Thread:
Lists: pgsql-performance
Hi,

Stephan Szabo wrote:

> On Sat, 16 Nov 2002, pginfo wrote:
>
> > Hi,
> >
> > Tom Lane wrote:
> >
> > > Josh Berkus <josh(at)agliodbs(dot)com> writes:
> > > > Here's a question: is the total size of the column a good indicator of the
> > > > sort_mem required?   Or does the rowsize affect it somehow?
> > >
> > > It will include all the data that's supposed to be output by the sort...
> > > both the key column(s) and the others.
> > >
> >
> > Hmm it is not clear for me.Let we have all data.
> > If I make sort by S.OP ( it is INT) it take < 6 sek for sort.
> > I think we move all this data anly the number of comparation is by INT. I think
> > the number of comparation
> > is ~ n * ln(n).
> > If we sort by S.IDS_xxx we have also n*ln(n) comparations but in
> > varchar(string).
> > I don't think that it can take 50 sek.
> >
> > Is it not so?
>
> Have you tried setting up another database in "C" locale and compared the
> timings there?  I'd wonder if maybe there's some extra copying going on
> given the comments in varstr_cmp.

No, I do not have any info about it.I will see if it is possible ( the data are not
so simple).
If it is possible I will make the tests.
Have no one that have 700K row in thow tables?
It is simple to test:
1. Run query that returns ~700K rows from this tables.
2. Make sort.

It is interest only the sort time!

regards,
Ivan.



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