Understanding Application-Based Assembly mode

The Application-Based Assembly (ABA) mode of operation provides significant runtime performance advantages over the alternative Rules Assembly (RA) cache approach.

Applications can operate using:

• Fully Application-Based Assembly cache mode - the default for new applications
• Fully Rules Assembly cache mode - the equivalent to normal operations in PRPC V6.2 SP2 and prior versions
• Mixed mode - used for applications transitioning towards fully ABA operation.

Note: Pega 7 applications should use virtual rules table (VTable) mode. This is because the assembly cache engine blends the benefits of VTable with ABA:

• UI (stream aspect) rules run using the Application-Based Assembly mode
• All other rule types run in VTable

Prconfig settings

Like other prconfig settings, the set prconfig value can be saved in the prconfig.xml file or as a specially-formatted Dynamic System Setting data instance. See How to create or update a prconfig setting.

• If the prconfig setting is RA for Rules Assembly mode, the Disable application-based assembly and use legacy caching check box is ignored and the requestor operates in Rules Assembly mode.
• Similarly, if the prconfig setting is AC for ABA mode, the Disable application-based assembly and use legacy caching check box is ignored and the requestor operates in ABA mode.
• If the prconfig setting is missing or Mixed, the Disable application-based assembly and use legacy caching check box determines the mode: cleared for ABA mode or selected for Rules Assembly mode.

Caution: This setting must have the same value for all nodes in a cluster.

Fully Application-Based Assembly cache mode

Fully ABA cache mode is sometimes referred to as AppCentric mode.

An application operates in Fully ABA cache mode if:

• The Revert check box on the Settings tab is not selected for every access group that references the application
• The prconfig.xml setting fua/assemblyCacheMode is set to AC

Note: The default setting of fua/assemblyCacheMode is AC. When using this default setting, you cannot revert back to any previous generation caching mode, such as Rules Assembly mode.

When operating in this mode, the ruleset list is ordered using the ABA model for all requestors and all other operations that use a ruleset list. The ABA cache is used to retrieve assembled rules.

ABA operation provides a marked performance improvement over Rules Assembly mode.

Fully Rules Assembly cache mode

An application operates in Fully Rules Assembly cache mode if:

• The Revert check box on the Settings tab is selected for all access groups that reference the application
• The prconfig.xml setting fua/assemblyCacheMode is set to RA

This mode exactly matches ruleset list ordering and caching on that was implemented prior to PRPC V6.3. Run-time execution is normally slower than ABA mode. The Rules Assembly cache is used, and the ABA cache is not used.

This mode is suitable for applications that do not meet the restrictions of ABA mode.

Mixed mode

An application operates in Mixed mode if:

• The Revert check box on the Settings tab is selected on some, but not all, of the access groups that reference the application
• The fua/assemblyCacheMode is set to Mixed

Mixed mode is suitable for applications that meet the requirements of ABA mode, but are in transition towards fully ABA operation. Users in either mode will experience identical functional results, but those accessing the application in Rules Assembly mode may experience poorer performance.

Restrictions

All newly created Pega 7 applications are structured to work properly with both ABA mode and VTable. Additionally, any existing applications developed in versions prior to PRPC V6.3 are also qualified to use full ABA mode and VTable.

Note: Override rulesets are not supported in ABA. For any access group that refers to an application with override rulesets:

1. Run Mixed mode.
2. Set Previous generation caching mode.

For localized and branch rulesets, the order of the ruleset list differs slightly when in ABA mode and when in Rules Assembly mode. This means that although it is highly unlikely when following localization best practices, it is still possible that rule resolution can pick a different rule when in ABA mode compared to Rules Assembly mode, leading to unexpected and incorrect results.

For details on how the ruleset lists differ, see How the system assembles and uses your RuleSet list.

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