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Starting in Hawthorne, there was a PersistentGradesEnabledFlag flag. When enabled, grades would be persisted in dedicated MySQL tables. They would only be re-calculated from scores when necessary. This improved performance and unlocked the development of in-demand features like the write-able grade book, but the system was still opt-in for each Open edX instance. When a instance operator enabled persistent grades, they’d also need to run the backfill (described below) in order to fill up the new tables.
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