How to Populate the Access Gen Caches after Installation (aka Configuring the Task Manager)

The Access Gen Task Manager is a batch utility provided to supplement the daytime activity of Access Gen users. Its primary function is to extract or refresh the model structure data and action diagrams out of normal working hours into the cache structures that are used by Access Gen . Help on using the Task Manager is available in the Task Manager User Manual or can be called directly from the software.

To understand how to configure the Task Manager to get the most out of Access Gen an explanation of how the Access Gen 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 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 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 is first installed there would need to be a Model Structure Cache extract performed for each model to be browsed.

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 request is made, Access Gen 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 does find the action diagram in the cache, then it first checks the last updated timestamp of the cached version against the encyclopedia version and 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 then 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 It is therefore not possible to see an out of date version of an action diagram.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 (note, make sure that the Use A/B Cache check box is checked under the Cache menu drop down in the client - this will be defaulted to checked each time the client is opened. If this check box is cleared then Access Gen will extract the action diagram from the encyclopedia every time a browse request is made).

The Model Structure Cache is stored in a directory called 'Models' located under the directory where the Access Gen server has been installed. Further sub-directories of that directory store the Action Diagram Cache. The directories and files are identified primarily by the model ID they apply to.

The primary function of the Access Gen Task Manager 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. It allows the administrator to maintain and execute schedules, which are made up of tasks. Each task is set up to extract information from a specific model. A task can extract information in four different ways:

Model Structure Cache Refresh. This will extract any changes made to the model structure since the last extract, also known as an Incremental Refresh.

Model Structure Cache Refresh with Force. This will re-extract all structure information for the chosen model, also known as a Forced Extract.

Action Diagram Cache Refresh. This will extract new and changed action diagrams to the Action Diagram Cache up to the limit set at execution.

Action Diagram Cache Refresh with Force. This will extract action diagrams to the Action Diagram Cache up to the limit set at execution regardless of whether that action diagram already exists in the Action Diagram Cache.

A task can also be set up to run daily (a Recurring task) or once only (a Single Run task). When Access Gen is first installed, both parts of the cache are empty. As previously explained, 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 client on a model-by-model basis or in batch via the Task Manager, with a task for each model. 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 use the Task Manager to set up daily incremental Model Structure Cache extract tasks for all models, scheduled to process out of normal hours.

For the Action Diagram Cache, a different strategy needs to be adopted. As stated, when Access Gen 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 will have to extract the action diagram from the encyclopedia until the cache is brought up to date.

When setting up tasks under the Task Manager to populate the Action Diagram Cache, there are a couple of options that need to be taken into account. One is the Force Extract option and the other is the limit of processed action diagrams to impose for the task execution (since extracting action diagrams can be a lengthy process, this limit can be used to make sure that an action diagram cache extract task does not run for an unacceptably long time). When the Force Extract option is checked and the task executes, the contents of the Action Diagram Cache are ignored and the task simply extracts the first n number of action diagrams that it finds, where n is the limit of action diagrams to process. So if you have a daily task set up with the Force Extract option checked and the extract limit is set to say twenty, then each night when that task executes, it will extract the same twenty action diagrams. If you do not have the Force Extract option checked then the task will execute each night extracting only new or changed action diagrams - an incremental extract. So if you had one hundred action diagrams to extract in total and a daily task to extract twenty each night with the Force Extract option not checked, after five nights the Action Diagram Cache would be full and up to date and subsequent executions of the task would just re-extract action diagrams that have changed since the last extract was made or new ones that have been added.

When you first install Access Gen , a good strategy is to use the Task Manager to perform some 'Single Run' incremental Action Diagram Cache extracts that run at a period of quiet encyclopedia usage (e.g. over a weekend) where the Action Diagram extract limit is set to a high number. In this way a few once off tasks will bring the Action Diagram Cache up to date in a short time. Subsequent daily incremental tasks can be set up with a low limit to take care of day-to-day action diagram changes.