You may want to delete historical performance data if the up.time Archive process has timed out and data older than the Archive Policy still exists in the data store. You may also choose to manually delete historical performance data to free up the threads for regular monitoring that the up.time Archive process would occupy. Another reason to manually delete historical performance data is to shrink the size of the data store DataStore which is covered in the Shrinking your MySQL DataStore knowledge base article.
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