从官方文档http://cn.docs.mongodb.org/manual/ref...：
BSON Object Size
The maximum BSON object size is 16 megabytes.
这是指单文档限制16M吗？包括嵌入的子文档吗？
怪我咯2017-04-21 10:58:10
Yes, including embedded subdocuments.
This limit is to prevent a single document from being too large and occupying too much memory or network bandwidth when fully read. According to the current main developers of MongoDB, they do not plan to release this restriction, but will increase it moderately as the relative cost of computing resources decreases (cheaper memory, faster network).
Official explanation:
MongoDB limits the data size of inpidual BSON objects/documents. At the time of this writing the limit is 16MB.
This limit is designed as a sanity-check; it is not a technical limit on document sizes. The thinking is that if documents are larger than this size, it is likely the schema is not ideal. Further it allows drivers to make some assumptions on the max size of documents.
The concept is that the maximum document size is a limit that ensures each document does not require an excessive amount of RAM from the machine, or require too much network bandwidth to fetch. For example, fetching a full 100MB document would take over 1 second to fetch over a gigabit ethernet connection. In this situation one would be limited to 1 request per second.
Over time, as computers grow in capacity, the limit will be adjusted upward.