code: def search(self, start_ts, end_ts):
          
          for _id in self.doc_dict:
              entry = self.doc_dict[_id]
              if entry.ts <= end_ts or entry.ts >= start_ts:
                  yield entry.meta_dict
docs: Searches through all documents and finds all documents that were
          modified or deleted within the range.
  
          Since we have very few documents in the doc dict when this is called,
          linear search is fine. This method is only used by rollbacks to query
          all the documents in the target engine within a certain timestamp
          window. The input will be two longs (converted from Bson timestamp)
          which specify the time range. The start_ts refers to the timestamp
          of the last oplog entry after a rollback. The end_ts is the timestamp
          of the last document committed to the backend.