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poor join performance

poor join performance

2007-01-29       - By Becker, Holger

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Reply:     1     2  

Eduard M wrote:

> I have a query that does a simple join from 2 tables, on a
> foreign key. Both
> tables are about 1,000,000 rows each. The query takes about
> 11 seconds. It
> seems like way too long.
>
> select kar.id from per_karte kar, per_nodarbosanas nod where nod.id > kar.per
_nodarbosanas_id
>
> The query is executed from SQL Studio.
> If I limit the query to rowno < 500, it executes very fast.
>
> I wonder why the big query takes so long. Is it somehow related to
> transaction isolation level? Is database copying aside any
> temporary data,
> or looking into rollback segment while making that join?
>
> Eduard

Hi,

join selects always creates a result set in MaxDB.

So if in your case each row from one table hits one in the other
you gets a result set with 1 million rows and this might take 11
seconds.

Kind regards
Holger

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