Re: Estimating the Time required to Build Access Paths

[John Earl <johnearl@xxxxxxxxxxx>]

I've never seen any good algorithm that will predict path
rebuild times.  The information contained in EDTACCRBD
command is the closest I've seen, but it's accurracy can
vary wildly depending on the current system load.

If you have another box available you could copy the PF and
LF's to tape and practice on a similar box, but that would
only be a rough estimate.

We have done re-orgs like this in the past and some of the
things that we do are:

a)      It's faster to remove the logicals before the reorg and
then build them separately after the PF has been restored
(we actually do a RMVM rather than a DLTF).

b)      For Some strange reason, a CPYF to a new file is almost
always faster than a reorg (assuming you have the disk
space).  This is especially if the new file has no access
paths built over it (Just another reason not to key PF's!  
...but that's a debate for another time :)

c)      If you have removed the access paths, then you can manage
the rebuild order.  This will alow you to gaurantee acccess
path sharing (where possible), but also allow you to bring
the most important logicals online first.  This could have
the effect of lengthening the two hour window.

d)      If you're able to get a exclusive read only lock on the
PF before the two hour window, you can actually start the
CPYF ahead of time so that the new version of the file is
ready to be moved into production as soon as the two hour
window starts.


Hth,

jte



Al Barsa, Jr. wrote:
> 
> Hi,
> 
> I am currently working on a system that is very over utilized from both a
> performance and disk space perspective.  We are currently purging old data
> (delete phase), and then will have to reorganize files. Of course the
> system has many to many LFs.
> 
> I have a two hour window nightly from end of batch/backup to when the
> system has to be back for the users.
> 
> I am looking for any kind of algorithm or formula to help me assess how
> long the access path build portion of the re-org will take.
> 
> Any ideas?
> 
> Al
> 
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--
John Earl                       PowerTech Toolworks
johnearl@toolnet.com            www.toolnet.com
253-858-7388                    206-575-0711
PowerLock Network Security for the AS/400
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