At 07:21 AM 7/8/99 -0700, Michael L Gueterman wrote:
>  Even with Adager for your Image dataset, you're essentially unloading
>and reloading that particular dataset to decrease the capacity (with
>some assumptions thrown in there :)

While I cannot speak for Adager, this is not quite how the leading-edge
IMAGE database tools approach this task.

<plug alert>

For detail datasets, DBGeneral (and Adager I believe) utilize some
low-level file system routines to adjust the existing dataset's
file limit as well as allocating space to the file.  So essentially
the file is adjusted in-place without any movement of data.  The
time involved is basically the amount of time needed by the file
system to allocate/initialize the additional space added to the
file.

Decreasing capacity for details is essentially checking some
conditions and if the results will meet IMAGE requirements,
the detail set is simply 'trimmed' by pointing to the where
the new EOF should be and doing the appropriate FCLOSE.  Once
done, some housekeeping has to be done, but there is no data
movement.  Under some circumstances it may be necessary for
the user to reorganize the detail set to lower the high-water-mark
in order to achieve the desired reduced capacity.

For master datasets, the basic technique for changing capacity
involves building a new dataset with the appropriate attributes
and then simply reading the entries from the old set, calculating
their new hash location based upon the capacity change, and placing
them in the new file. Once done, the files are swapped around and
a number of other housekeeping activities are performed.

So while handling master sets may, on the surface, seem like an
unload/reload, the 3rd party tools use much more sophisticated
technology in conducting this task, which is why DBGeneral,
Adager and others are quite a bit faster then the old fashion
dbunload/dbload approach provided by IMAGE.

I hope my friends at Adager will chime-in to correct anything
I may have implied which is incorrect from their perspective.

<\plug>




/jf
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