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IDS Forum

Re: Do not set the PSORT_NPROCS ?

Posted By: FRANK
Date: Thursday, 25 July 2013, at 12:25 p.m.

In Response To: Re: Do not set the PSORT_NPROCS ? (Art Kagel)

Thanks Art!

One more question :-)

If
SHMVIRTSIZE is 1GB
DS_TOTAL_MEMORY is 500MB
and *PDQPRIORITY is not set in the session or server side.*

The available virtual shared memory size for all OLTP sessions is 1GB or
500MB?

Thanks,
Frank

On Tue, Jul 23, 2013 at 10:45 PM, Art Kagel <art.kagel@gmail.com> wrote:

> OK, here's the skinny on PDQPRIORITY versus PSORT_NPROCS for index builds
> and update statistics as I understand it:
>
> - If you do not or cannot set PDQPRIORITY to a positive value (ex:
>
> Workgroup Edition does not allow PDQPRIORITY) the setting PSORT_NPROCS is
>
> the only way to get multiple sort threads running.
>
> - PSORT_NPROCS - "officially" - can be set to any value from 2 to 10.
>
> Officially setting a value greater than 10 results in the equivalent of
>
> 10. The value set determines the number of parallel sort threads that are
>
> used.
>
> - My experience has been that you can set PSORT_NPROCS to any value you
>
> want and you will get that number of sort threads. I'm just saying... Try
>
> it for yourself.
>
> - If you set PDQPRIORITY to a positive value, you enable parallel
>
> processing overall and the Memory Grant Manager and parallel query manager
>
> determine the number of sort threads in an "optimal" way based on two sort
>
> threads per sort with the number of sorts equal to the number of partitions
>
> in the index for an index build. PDQPRIORITY overrides the PSORT_NPROCS
>
> setting.
>
> - The number of sorts for update statistics is not documented, but I
>
> suspect it has to do with the number of columns included in the command as
>
> well as other factors.
>
> - The percentage of resources represented by the session's effective
>
> PDQPRIORITY (throttled by MAX_PDQPRIORITY) is used to determine the amount
>
> of memory available for in-memory sorting during index builds and update
>
> statistics runs.
>
> - If PDQPRIORITY is zero, index builds use DS_NONPDQ_QUERY_MEM to
>
> determine how much memory to use for in-memory sorting. This can be up to
>
> 25% of DS_TOTAL_MEMORY. The default value if unset is 128KB. Update
>
> statistics uses DBUPSPACE still to determine memory for sorting according
>
> to the documentation. The default is 15MB.
>
> Art
>
> Art S. Kagel
> Advanced DataTools (www.advancedatatools.com)
> Blog: http://informix-myview.blogspot.com/
>
> Disclaimer: Please keep in mind that my own opinions are my own opinions
> and do not reflect on my employer, Advanced DataTools, the IIUG, nor any
> other organization with which I am associated either explicitly,
> implicitly, or by inference. Neither do those opinions reflect those of
> other individuals affiliated with any entity with which I am affiliated nor
> those of the entities themselves.
>
> On Tue, Jul 23, 2013 at 10:28 PM, FRANK <yunyaoqu@gmail.com> wrote:
>
> > Folks,
> >
> > I see the following rules on 11.70 info center.
> >
> > In rule 2: "Do not set the *PSORT_NPROCS* environment variable", What
> > negative impacts it would cause if we set the *PSORT_NPROCS* in index
> > creating process?
> >
> > Thanks,
> > Frank
> >
> > http://pic.dhe.ibm.com/infocenter/idshelp/v117/index.jsp
> >
> > You can often improve the performance of an index build by taking the
> > following steps:
> >
> > 1. Set PDQ priority to a value greater than 0 to obtain more memory than
> >
> > the default 128 kilobytes.
> >
> > When you set PDQ priority to greater than 0, the index build can take
> >
> > advantage of the additional memory for parallel processing.
> >
> > To set PDQ priority, use either the *PDQPRIORITY* environment variable
> >
> > or the SET PDQPRIORITY statement in SQL.
> >
> > 2. Do not set the *PSORT_NPROCS* environment variable. If you have a
> >
> > computer with multiple CPUs, the database server uses two threads per
> sort
> >
> > when it sorts index keys and *PSORT_NPROCS* is not set. The number of
> >
> > sorts depends on the number of fragments in the index, the number of
> >
> > keys, the key size, and the values of the PDQ memory configuration
> >
> > parameters.
> >
> > 3. Allocate enough memory and temporary space to build the entire index.
> >
> > --001a11c2bc0240d9fe04e238ab9a
> >
> >
> >
> >
>
> *******************************************************************************
> > Forum Note: Use "Reply" to post a response in the discussion forum.
> >
> >
>
> --089e0158acf0c4c8a304e238e501
>
>
>
> *******************************************************************************
> Forum Note: Use "Reply" to post a response in the discussion forum.
>
>

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