我正在使用MongoDB来聚合一些数据。查询也可以在错误消息中看到。虽然我使用$out将结果导出到另一个集合，但聚合失败。有什么建议吗？
OperationFailure: command SON([('aggregate', u'h'), ('pipeline',
[{'$unwind': '$hashtags'}, {'$group': {u'replied': {'$push': u'$replied'},
u'retweeted': {'$push': u'$retweeted'}, u'followers': {'$push':
u'$followers'}, u'user': {'$push': u'$user'}, u'date': {'$push':
u'$date'}, '_id': '$hashtags', '_ids': {'$push': u'$_id'}}}, {'$out':
'Hashtags'}]), ('allowDiskUse', True)]) failed: exception: BufBuilder
attempted to grow() to 134217728 bytes, past the 64MB limit.