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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 bulk_upsert(self, docs, namespace, timestamp):
 """Insert multiple documents into Elasticsearch."""

        def docs_to_upsert():
            doc = None
            for doc in docs:
                # Remove metadata and redundant _id
                index, doc_type = self._index_and_mapping(namespace)
                doc_id = u(doc.pop("_id"))
                document_action = {
                    '_index': index,
                    '_type': doc_type,
                    '_id': doc_id,
                    '_source': self._formatter.format_document(doc)
                }
                document_meta = {
                    '_index': self.meta_index_name,
                    '_type': self.meta_type,
                    '_id': doc_id,
                    '_source': {
                        'ns': namespace,
                        '_ts': timestamp
                    }
                }
                yield document_action
                yield document_meta
            if doc is None:
                raise errors.EmptyDocsError(
                    "Cannot upsert an empty sequence of "
                    "documents into Elastic Search")
        try:
            kw = {}
            if self.chunk_size > 0:
                kw['chunk_size'] = self.chunk_size

            responses = streaming_bulk(client=self.elastic,
                                       actions=docs_to_upsert(),
                                       **kw)

            for ok, resp in responses:
                if not ok:
                    LOG.error(
                        "Could not bulk-upsert document "
                        "into ElasticSearch: %r" % resp)
            if self.auto_commit_interval == 0:
                self.commit()
        except errors.EmptyDocsError:
            # This can happen when mongo-connector starts up, there is no
            # config file, but nothing to dump
            pass