Re: fragment elimination on query
Art S. Kagel wrote:
> For fragment elimination to take place you have to run with PDQPRIORITY
> >= 1
Are you sure this is correct Art? Here is a query I just ran to check
with PDQPRIORITY set to zero:
QUERY:
------
select * from customer where id=3
Estimated Cost: 1
Estimated # of Rows Returned: 1
1) informix.customer: INDEX PATH
(1) Index Keys: serialno (Serial, fragments: 3)
Lower Index Filter: informix.customer.id = 3
Ben.
That query didn't use PDQ or Fragment elimination, it did an index lookup to
get the required data.
PDQPRIORITY needs to be set so enough threads will be started which will
scan each fragment. Note that you need to use fragment by expression to take
advantage of fragment elinination and not round robin as the optimiser
doesn't know which fragment the data it in.
How is your table and indices built?
Regards
Colin
There are 10 types of people in the world, those that understand binary and
those that don't
>From: Ben Thompson <ben@nomonitorsoftspam.com>
>To: informix-list@iiug.org
>Subject: Re: fragment elimination on query
>Date: Fri, 07 Jul 2006 09:20:49 +0100
>
>Art S. Kagel wrote:
>
> > For fragment elimination to take place you have to run with PDQPRIORITY
> > >= 1
>
>Are you sure this is correct Art? Here is a query I just ran to check
>with PDQPRIORITY set to zero:
>
>QUERY:
>------
>select * from customer where id=3>
>Estimated Cost: 1
>Estimated # of Rows Returned: 1
>
> 1) informix.customer: INDEX PATH
>
> (1) Index Keys: serialno (Serial, fragments: 3)
> Lower Index Filter: informix.customer.id = 3
>
>Ben.
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Ben Thompson wrote:
> Art S. Kagel wrote:
>
>> For fragment elimination to take place you have to run with
>> PDQPRIORITY >= 1
>
>
> Are you sure this is correct Art? Here is a query I just ran to check
> with PDQPRIORITY set to zero:
Apparently not as sure as I once was. John Miller agrees with you, and
obviously it worked below. IB I was thinking of parallel fragment scan
which is invoked when PDQPRIORITY is set to 1 or LOW or greater.
<SIGH!> Only 51 and my mind is already going! Very sad... ;-{
Art S. Kagel
> QUERY:
> ------
> select * from customer where id=3>
> Estimated Cost: 1
> Estimated # of Rows Returned: 1
>
> 1) informix.customer: INDEX PATH
>
> (1) Index Keys: serialno (Serial, fragments: 3)
> Lower Index Filter: informix.customer.id = 3
>
> Ben.