When a student submits a problem answer, the state is stored in a
StudentModule record containing answer, score, correctness, etc. The
record, though, is updated in multiple steps within the single request
(first the grade is updated, then the state is updated separately).
Each partial save would trigger a separate StudentModuleHistory record
to be stored resulting in duplicate and inaccurate historical records.
This solution uses the RequestCache to track within a request thread
which StudentModules are updated and a single corresponding
StudentModuleHistory id. If multiple update actions occur within the
request cycle, then modify the history record that was already
generated to ensure that each submission only results in one
StudentModuleHistory record.
This issue and its solution were discussed in:
https://discuss.openedx.org/t/extra-history-record-stored-on-each-problem-submission/8081
ff0c1d57da