The problem, solution, and benefits
If an administrator sets a list box as an external one in the list box manager interface, its values are fetched dynamically by running an associated script on the server side. This happens whenever an external list box is accessed (by hovering a mouse cursor, for example) by a user in a Submit, Show, or Transition form. Running that script every time while accessing the list box generally results in a delay in populating the list box values in the forms, but that depends on what the script is doing to fetch the values. To overcome this delay, a list box values cache was introduced in Rational Change Version 5.3.
Enabling a list box values cache avoids having the server run an external script every time. This results in better response time from your server while it is populating list box values.
How the external list box value cache works
This is an enhancement to the existing external list box capability. Rational Change now builds a cache of external list box values by running all of the associated list box scripts when the server starts. This helps reduce the overhead of executing the scripts every time that the list box attribute is accessed, which reduces server response time.
This list box cache is either created or updated in two situations:
- During startup of the server, the cache is created
- On reloading the configuration data, if the cache is not already present, it is created. If it is already present, it is updated by running the associated script for every external list box attribute.
When to use and not to use a cache
There are few scenarios where external list box values caching is not recommended:
- While fetching the data from an external source, such as a database
- When reading from a file where content changes frequently
- If the content is user-specific and if the script requires user information as an argument
Therefore, turning caching on is not recommended when the script is returning the data that is very dynamic in nature. Keeping caching on in such situations can return outdated data.
How to configure the external list box values cache
You can configure the external list box values cache through the pt.cfg configuration file on a Rational Change server. This configuration entry provides a way to turn the caching on or off.
Add the following configuration entry to the pt.cfg file to manage the external list box values cache:
These are the valid values for this configuration entry:
- Turns the caching on.
- Turn the caching off.
This needs to be followed by loading the configuration data from the Admin interface.
By default, this entry does not exist in the pt.cfg file. Therefore, the administrator must add it to enable this feature.
- Start at the Rational Change page on developerWorks to learn about features and benefits, get product details and information on related Rational products, and to find more technical articles and where to get support. For other detailed instructions, see Managing list boxes and the Version 5.3 information center.
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