Fw: Sub SELECTS

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I have a select query with 2 sub selects.
When I run that query CPU usage goes to 98% for postgres.
Does sub selects eat more resources and slower the queries?
Is there any alternatives to sub selects?

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Re: Fw: Sub SELECTS

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on 9/25/02 8:51 AM, waruna@nirmani.com purportedly said:

I have a select query with 2 sub selects.
When I run that query CPU usage goes to 98% for postgres.
Does sub selects eat more resources and slower the queries?
Is there any alternatives to sub selects?

That high CPU usage seems odd. I wouldn't think that even extremely complex
queries would effect CPU that much, unless there are other factors such as
low memory that would contribute.

If any case, if you post the query and table schemas we might be able to
make suggestions. Sub-selects are generally fairly efficient unless the
results from the sub-selects are particularly large. Postgres may not be
able to use indexes on sub-select results, I am not sure.

Keary Suska
Esoteritech, Inc.
"Leveraging Open Source for a better Internet"


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on 9/25/02 8:51 AM, waruna@nirmani.com purportedly said:

I have a select query wit=
h 2 sub selects.

When I run that query CPU usage goes to 98% for postgres.

Does sub selects eat more resources and slower the queries?

Is there any alternatives to sub selects?

Re: Fw: Sub SELECTS

>>>>> "Waruna" == Waruna Geekiyanage writes:

Waruna> I have a select query with 2 sub selects. When I run that
Waruna> query CPU usage goes to 98% for postgres. Does sub
Waruna> selects eat more resources and slower the queries? Is
Waruna> there any alternatives to sub selects?

You are going to have to give us a clue as to what those sub-selects
are and what they are doing. If there is an "order by" clause
anywhere, that could cause high CPU. If the query is not using
indicies, that might cause a problem. Have you tried EXPLAIN?

roland
--
PGP Key ID: 66 BC 3B CD
Roland B. Roberts, PhD RL Enterprises
roland@rlenter.com 76-15 113th Street, Apt 3B
roland@astrofoto.org Forest Hills, NY 11375

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