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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _doCleanup(self):
 """ Perform any periodic database cleanup tasks. @returns: Deferred """

        # pass on this if we're not configured yet
        if not self.configured_url:
            return

        d = self.changes.pruneChanges(self.master.config.changeHorizon)
        d.addErrback(log.err, 'while pruning changes')
        return d