Thread: Info on explain output

Hi,

I am trying to optimise a complex query adding explicit joins and creating
indices. I am going through the EXPLAIN output (~70 lines) but am fairly new
at reading these.

Are there any good rules of thumb of things one should be looking out for in
EXPLAIN output? ie <blah> means that an index would be good here etc

I have read through the docs for EXPLAIN, but I was wondering if there were
any more detailed descriptions or docs on the subject.

Thanks for any help

adam


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Adam Witney wrote:
> Hi,
>
> I am trying to optimise a complex query adding explicit joins and creating
> indices. I am going through the EXPLAIN output (~70 lines) but am fairly new
> at reading these.
>
> Are there any good rules of thumb of things one should be looking out for in
> EXPLAIN output? ie <blah> means that an index would be good here etc
>
> I have read through the docs for EXPLAIN, but I was wondering if there were
> any more detailed descriptions or docs on the subject.
>
> Thanks for any help
>
> adam
>
>
> --
> This message has been scanned for viruses and
> dangerous content by MailScanner, and is
> believed to be clean.
>
>
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>

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Adam,

> > Are there any good rules of thumb of things one should be looking
> out for in
> > EXPLAIN output? ie <blah> means that an index would be good here
> etc

Also try:
1) Various articles on Techdocs.postgresql.org
2) Ewald G.'s PostgreSQL Book

Explain output is not that easily converted into a plan of action ...
otherwise, Postgres would have automated it, neh?   You have to get a
feel for what looks good and bad dynamically.

-Josh Berkus