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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 _flush(self, commit=True, using=None):
 """ Flushes the internal cache, either to the memcache or rolls back """

        if commit:
            # XXX: multi-set?
            if self._uses_savepoints():
                self._commit_all_savepoints(using)
            c = self.local.mget('%s_%s_*' %
                                (self.prefix, self._trunc_using(using)))
            for key, value in c.items():
                self.cache_backend.set(key, value, self.timeout)
        else:
            if self._uses_savepoints():
                self._rollback_all_savepoints(using)
        self._clear(using)
        self._clear_sid_stack(using)