ExpressionRef Library context_values performance issue

[AymericGrassart]

A performance slowdown has been identified when executing referenced CQL statements under certain conditions.

Assumptions

• Execution results of ExpressionDef expressions are cached in their library context.
• ExpressionRef expressions use those cached results.

Issue

The CQL below performs in a degraded, non-cached way. We suspect the wrong context is used to store or lookup the cached context values when ExpressionRefs cross library contexts.

Test

CommonLib3:

library Common3
using Simple version '1.0.0'
context Patient

define function ExpensiveFunction():
  First(expand Interval[1, 100000])

define ExpensiveStatement:
  ExpensiveFunction()

define ExpensiveStatementRef:
  ExpensiveStatement union 
  ExpensiveStatement union 
  ExpensiveStatement union 
  ExpensiveStatement union 
  ExpensiveStatement

Using CommonLib3:

using Simple version '1.0.0'
include Common3 called common3
context Patient

define ExpensiveStatementRef: common3.ExpensiveStatementRef

The result of the library-test shows the perf degradation as if ExpensiveStatement was not being cached:

$ npm test

  CommonLib3
    ✔ should be able to execute an expensive expression (123ms)

  Using CommonLib3
    ✔ should execute expression from included library at similar cost (565ms)
    ✔ should execute expression directly from included library at similar cost (291ms)

Solution

?

Please note there are no changes to src code, only tests were added to demonstrate the perf issue. Looking for feedback.

We hope that a fix can be identified and included with this PR.

Pull requests into cql-execution require the following.
Submitter and reviewer should ✔ when done.
For items that are not-applicable, mark "N/A" and ✔.

Submitter:

• This pull request describes why these changes were made
• Code diff has been done and been reviewed (it does not contain: additional white space, not applicable code changes, debug statements, etc.)
• Tests are included and test edge cases
• Tests have been run locally and pass
• Code coverage has not gone down and all code touched or added is covered.
• Code passes lint and prettier (hint: use npm run test:plus to run tests, lint, and prettier)
• All dependent libraries are appropriately updated or have a corresponding PR related to this change
• cql4browsers.js built with npm run build:browserify if source changed.

Reviewer:

Name:

• Code is maintainable and reusable, reuses existing code and infrastructure where appropriate, and accomplishes the task’s purpose
• The tests appropriately test the new code, including edge cases
• You have tried to break the code