Re: long runtimes cured by cutting hash_area_size by 90% - ???

I'll second Wolfgang's call for the runtime tkprof plans.

Was this a parallel query ? Very nasty things can happen with PQ and multiple concurrent hashes. (And just plain nasty things can happen with concurrent hashes and serial queries).

Was the test repeatable ? The difference could have been due to a large amount of delayed block cleanout on the first run
that didn't happen on the second.

Was event 10053 switched on for the first query and not the second ? I've had the
'apparent optimisation time' switch between 1.05 seconds and 10 minutes on a complex query because of a very slow write to trace file.

Regards

Jonathan Lewis
http://www.jlcomp.demon.co.uk

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The Co-operative Oracle Users' FAQ
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• Original Message ----- To: "Multiple recipients of list ORACLE-L" <ORACLE-L_at_fatcity.com> Sent: 08 April 2003 05:43

> Hash_Area_Size runtime
> 10,000,000 6:16 ( 6+ mins )
> 1,000,000 0:15 ( 16 secs)
>
> Why?
> Isn't bigger always better for hash_area_size?
> Is another param affected?
>
> That's the only param that changed, via alter session.
>
> Oracle 8.1.7, Sun/Solaris, 8 cpus, lots & lots of memory,
> no other queries, or 3 concurrent: same runtime.
>
> The query joins 9 tables, one has 1.8M rows, the others under 60k
rows.
>
> Explain Plan shows 5 nested loops, 3 hash joins, and no diff between
> plans with the 2 values.
>
> Chris Barr
>

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