From: | Jean-Luc Lachance <jllachan(at)nsd(dot)ca> |
---|---|
To: | Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> |
Cc: | Oleg Bartunov <oleg(at)sai(dot)msu(dot)su>, Shaun Thomas <sthomas(at)townnews(dot)com>, Gunther Schadow <gunther(at)aurora(dot)regenstrief(dot)org>, pgsql-general(at)postgresql(dot)org |
Subject: | Re: Critical performance problems on large databases |
Date: | 2002-04-12 15:52:36 |
Message-ID: | 3CB702C4.64C1EFE5@nsd.ca |
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Lists: | pgsql-general |
Bruce Momjian wrote:
>
> Oleg Bartunov wrote:
> > The big issue with LIMIT,OFFSET is that it still use all rows
> > for sorting. I already suggested to use partial sorting to avoid
> > sorting all rows if one selected only first 20 row, for example.
> > It's very important for Web applications because web users usually
> > read first 1-2 pages. Our experimnets have shown 6 times performance
> > win when using partial sorting.
>
> We do have this TODO item:
>
> * Allow ORDER BY ... LIMIT to select top values without sort or index
> using a sequential scan for highest/lowest values
It may not be wise to disregard the index if there is one for the ORDER
BY.
JLL
>
> --
> Bruce Momjian | http://candle.pha.pa.us
> pgman(at)candle(dot)pha(dot)pa(dot)us | (610) 853-3000
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