From: | Bruce Momjian <maillist(at)candle(dot)pha(dot)pa(dot)us> |
---|---|
To: | andreas(dot)zeugswetter(at)telecom(dot)at (Andreas Zeugswetter) |
Cc: | hackers(at)postgreSQL(dot)org |
Subject: | Re: [HACKERS] sorting big tables :( |
Date: | 1998-05-22 14:24:20 |
Message-ID: | 199805221424.KAA29226@candle.pha.pa.us |
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Lists: | pgsql-hackers |
>
>
> > I have an idea. Can he run CLUSTER on the data? If so, the sort will
> > not use small batches, and the disk space during sort will be reduced.
>
> I think a real winner would be to use an existing index. This is what others do
> to eliminate a sort completely. Of course the optimizer has to choose what is cheaper
> on a per query basis (index access or sort of result set).
> result set small --> use sort
> result set large --> use available index
Keep in mind an index is going to be seeking all over the table, making
the cache of limited use. Sometime, when doing a join, the optimizer
chooses a sequential scan rather than use an index for this reason, and
the sequential scan is faster.
--
Bruce Momjian | 830 Blythe Avenue
maillist(at)candle(dot)pha(dot)pa(dot)us | Drexel Hill, Pennsylvania 19026
+ If your life is a hard drive, | (610) 353-9879(w)
+ Christ can be your backup. | (610) 853-3000(h)
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