We recently started using a modify log record in WiredTiger, which has the interesting property that it's not idempotent. i.e: if the record is re-applied on top of a data change that already includes a change, or if a log record is applied multiple times we would end up with invalid data.
We should inspect the code looking for cases where log records might be applied when they shouldn't be to ensure there aren't any bugs. We should also extend our recovery testing to cover cases where modify records are logged. The log record types are WT_LOGOP_ROW_MODIFY and WT_LOGOP_COL_MODIFY