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Unless the customer has legal or business requirements to keep track of what operations has been performed you can simply delete all entries before a certain date to reduce the file size, as they are not used for anything after they have been processed. Deleting an entry will delete the XML for that entry, so it will not leave any "orphaned records".
If you wan't want to periodically perform this clean up, then you can create a scheduled SQL job to perform the clean up as desired intervals.
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