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Support Article

Declare rule execution is very slow for a use case



System Hangs for one particulare use case in PRPC 6.2sp2 after DSM( Decision Strategy Manager ) upgrade; This issue was intermittent but after DSM upgrade this is always happening. Before DSM upgrade issue was encountered, but after DSM upgrade it is failing because of stuck threads.

Error Messages

No Error ( slow response )

Steps to Reproduce

Issue is consistently reproduced for a particular use case. In a screen flow user enter all the details before the submission and it taks about 3-5mins for the screen to return.

Root Cause

The root cause of this problem is a defect in Pegasystems’ code/rules.

Forward chaining is an algorithm executed between activity steps which analyzes property value changes and executes Rule-Declare-Expressions rules (and other forward chaining rules like Rule-Declare-OnChange and Rule-Declare-Constraints). This process requires aggregating all of the property changes since the last forward chaining, resolving which Expressions need to be evaluated due to a change in one or more of their input properties, and putting these Expressions into the correct and efficient order. The resulting list is then handed off for execution in the Pega engine.

The forward chaining algorithm is well suited for many use cases and permutations, but does not deal well with this use cases. This application makes heavy use of context-free forward chaining, using Reference Properties inside page lists or page groups. There is a non-linear growth in elapsed time needed to evaluate these chains as the number of properties and references grows. this is why higher degrees of performance degradation is observed. 


HFIX-20276 & HFIX-20203 address the problem. same use case returned within 20-25secs after the HFIXes.

Published January 31, 2016 - Updated October 8, 2020

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