AW: *Max4GB or *Max1TB

Hi,

but be aware, if you create additional indexes with the same key fields,
additional access paths are created! An index with a 64K page size will not
share an access path with a logical file with a smaller page size.
Additioal access paths may affect performance as soon as a record gets
updated, because all access paths on the based table must be updated.
If there are already 250 logical files (with may be 150 different access
paths), I'd reconsider to add additional access paths.  

If you create an index first and after a logical file with the same (or
less) key fields in the same sequence the logical file will share the access
path with the index and also adopt the larger page size.

An SQL index will only share the access path with an other SQL index that
has the same key fields in the same sequence. An SQL index with less key
fields, but in the same sequence will NOT share an access path with an other
index.

An SQL index can be used with native I/O like any other keyed logical file.
That means it can specified in RPG in the F-Specs like any logical file.

In this way, I'd replace keyed logical files without joins or select/omit
clauses through SQL indexes. 

After creating all the new indexes, I'd delete all existing logical files
and recreate them, to allow them to share access path and the larger page
size with the new indexes.

Birgitta

"If you think education is expensive, try ignorance"
(Derek Bok)
 
-----Ursprüngliche Nachricht-----
Von: midrange-l-bounces@xxxxxxxxxxxx
[mailto:midrange-l-bounces@xxxxxxxxxxxx] Im Auftrag von Clare Holtham
Gesendet: Montag, 10. April 2006 10:26
An: Midrange Systems Technical Discussion
Betreff: Re: *Max4GB or *Max1TB

Not BPCS is it???
Seriously, I would certainly change them all to Max1TB, it does improve 
performance. But Walden is right, it is worth having SQL indexes for the 
most used ones too. It's well worth just running the database monitor over 
the app for a while and then creating the indexes recommended.

cheers,

Clare

Clare Holtham
Director, Small Blue Ltd - Archiving for BPCS
Web: www.smallblue.co.uk
IBM Certified iSeries Systems Professional
Email: Clare.Holtham@xxxxxxxxxxxxxxx

----- Original Message ----- 
From: <pnelson@xxxxxxxxxx>
To: "Midrange Systems Technical Discussion" <midrange-l@xxxxxxxxxxxx>
Sent: Sunday, April 09, 2006 12:05 AM
Subject: Re: *Max4GB or *Max1TB


>I think I'll rip through and change everything in one fell swoop. Next
> weekend is Easter, and they won't have anybody working.
> -- 
>
> Paul Nelson
> Arbor Solutions, Inc.
> 708-670-6978  Cell
> pnelson@xxxxxxxxxx
>
>
>
>
> Vernon Hamberg <vhamberg@xxxxxxxxxxx>
> Sent by: midrange-l-bounces@xxxxxxxxxxxx
> 04/08/2006 05:59 PM
> Please respond to
> Midrange Systems Technical Discussion <midrange-l@xxxxxxxxxxxx>
>
>
> To
> Midrange Systems Technical Discussion <midrange-l@xxxxxxxxxxxx>
> cc
>
> Subject
> Re: *Max4GB or *Max1TB
>
>
>
>
>
>
> Hi Paul
>
> I searched the iSeries support site for ACCPTHSIZ and found a couple
> things. One has to do with access path sharing--
>
> In R410, the default for Access path size (ACCPTHSIZ) changed to
> *MAX1TB rather than *MAX4GB on the CRTLF and CRTPF commands and in
> the SQL CREATE INDEX statement. Most existing access paths have an
> attribute of *MAX4GB. These access paths cannot be shared by access
> paths with an attribute of *MAX1TB. For access path sharing to occur,
> change existing access paths to ACCPTHSIZ(*MAX1TB) or specify
> ACCPTHSIZ(*MAX4GB) on the new access paths.
>
> The other is from "The System Administrator's Companion to AS/400
> Availability and Recovery"
> Redbook http://www.redbooks.ibm.com/redbooks/pdfs/sg242161.pdf
> section 16.14, where it says the 4-byte index is supposed to
> circumvent seize locks. It also says not to mix the 2 kinds of indexes.
>
> HTH
> Vern
>
> At 10:16 AM 4/8/2006, you wrote:
>
>>I've got a client experiencing performance problems with his software
>>package. Many of the files have a huge number of logicals built over them
>>for various purposes. One has over 250 logicals and joined logicals. All
>>of the files are defined as having an acces path size of 4GB.
>>
>>This system is also being hit with lots of ODBC requests that were
>>permitted to be built by the previous IT manager (windoze bigot).
>>
>>I know how to throttle back the ODBC impact, but should I change the
> acces
>>path size to 1TB for just the logicals or both the physical and its
>>associated logicals to improve the overall performance?
>>
>>Thanks
>>--
>>
>>Paul Nelson
>>Arbor Solutions, Inc.
>>708-670-6978  Cell
>>pnelson@xxxxxxxxxx
>>--
>>This is the Midrange Systems Technical Discussion (MIDRANGE-L) mailing
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