使用 pymongo 时有时会遇到提示如下的错误:
File "/usr/local/lib/python2.7/dist-packages/pymongo/cursor.py", line 1090, in next
if len(self.__data) or self._refresh():
File "/usr/local/lib/python2.7/dist-packages/pymongo/cursor.py", line 1022, in _refresh
self.__uuid_subtype))
File "/usr/local/lib/python2.7/dist-packages/pymongo/cursor.py", line 958, in __send_message
self.__compile_re)
File "/usr/local/lib/python2.7/dist-packages/pymongo/helpers.py", line 113, in _unpack_response
error_object)
OperationFailure: database error: Executor error: Overflow sort stage buffered data usage of 33597009 bytes exceeds internal limit of 33554432 bytes
为什么会出现这样的错误呢？ 原来 mongodb 限制了在内存中进行 sort 操作（无法使用索引的情况下）时所使用的最大内存大小，默认是 32 M(33554432 bytes)。
如果要修改这个限制的话，可以通过如下的 mongo 命令进行修改，比如修改为 50 M(52428800 bytes):
> use admin
> db.adminCommand({setParameter: 1, internalQueryExecMaxBlockingSortBytes: 52428800})
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