The following is intended to help Access Gen (TSO) administrators gain an
understanding of the purpose of the Access Gen (TSO) Batch Extract Utility and
how it can be used to help get the most out of Access Gen (TSO). It does not
contain instructions on how to configure the utility which can be found in the
User and Technical Manual that was supplied with the software. There is also
an electronic copy of this manual on the installation CD.
The Batch Utility has been designed to supplement the online daytime activity
of Access Gen (TSO) users. Its primary function is to maintain the cache
structures that are used by Access Gen (TSO) to deliver up to date information
in response to browse requests. To best explain its significance, an
explanation of how the Access Gen (TSO) caching works is first required.
The cache actually consists of two parts, the Model Structure Cache and the
Action Diagram Cache. In order to use Access Gen (TSO) to browse a specific
model, then its structure has to have been extracted into the Model Structure
Cache beforehand. The Model Structure Cache allows Access Gen (TSO) to search
for objects very quickly and also allows for the fast object expansion. All
other functions that are performed (e.g. version, impact analysis, checkout
info etc.) get their information directly from the encyclopedia via highly
optimised queries.
When Access Gen (TSO) is first installed there would need to be a Model
Structure Cache extract performed for each model to be browsed. Once this
initial extract has been performed, subsequent extracts of a model will only
refresh the Model Structure Cache with the changes that have been applied
since the extract was last run.
The Action Diagram Cache is different from the Model Structure Cache in that
it does not need to be populated to allow a user to browse a model. It only
gets used in response to a user browse or compare request for an action
diagram.
When this browse or compare request is made, Access Gen (TSO) first looks in
the Action Diagram Cache for that action diagram. If it does not find it then
it goes to the encyclopedia and extracts it. This process can take a
relatively long time, but once extracted, the cache is updated with the action
diagram and it is then presented to the user. If Access Gen (TSO) does find
the action diagram in the cache, then it checks the last updated timestamp of
the cached version against the encyclopedia version – if the timestamps match
it displays the action diagram from the cache straight away. If the timestamps
do not match then the action diagram is re-extracted from the encyclopedia,
the cached version is updated and the action diagram is displayed. It is
therefore not possible to see an out of date version of an action diagram.
To see how fast browsing an action diagram is via the cache compared to an
extract from the encyclopedia, browse one that has not been extracted and then
browse it again straight after. The second browse should be very fast compared
to the first. The Model Structure Cache is stored in the TLIB Access Gen (TSO)
dataset. The Action Diagram cache is stored in the ADLIB Access Gen (TSO)
dataset.
The primary function of the Access Gen (TSO) Batch Utility is to supplement
daytime activity by refreshing the Model Structure Cache and the Action
Diagram Cache out of normal working hours without the need for user
intervention.
When Access Gen (TSO) is first installed, both parts of the cache are empty.
As explained overleaf, the Model Structure Cache has to be extracted for a
model to be browsed. This can be initiated either on-line from the Access Gen
(TSO) front panel using the Refresh Model Cache option or in batch via the
Batch Utility.
A typical approach on day one of installation may therefore be to request
on-line Model Structure Cache extracts for the models likely to be browsed
that day and then configure the Batch Utility to run nightly incremental
extracts for all models to be browsed, scheduled to process out of normal
hours (incremental means that only the changes made to a model since the last
time the cache was refreshed are extracted).
The SYSIN dataset is used to maintain a list of the models to be processed by
the Batch Utility.
For the Action Diagram Cache, a different strategy needs to be adopted. When
Access Gen (TSO) is first installed the action diagram cache is empty. This
means that in most cases browse requests for action diagrams are going to take
longer than normal, as Access Gen (TSO) will have to extract the action
diagram from the encyclopedia until the cache is brought up to date.
When running the Batch Utility a parameter can be used to govern the maximum
number of action diagrams that are extracted in a single run. This parameter
is called the ADLIM parameter and its default value at installation is 100.
When you first install Access Gen (TSO), a good strategy is to use the ADLIM
parameter to schedule and control large Action Diagram Cache extracts at times
of quiet encyclopedia usage (e.g. over a weekend) since an elapsed time of
several hours can be expected to process the action blocks for a large number
of models. Once the Action Diagram Cache is up to date the ADLIM parameter can
be reduced again. For a large and busy encyclopedia, 100 is usually enough to
keep up with the day to day changes to action diagrams that occur or the
occasional addition of a new model.