Description
The current limits page at http://docs.mongodb.org/manual/reference/limits/ does not contain the upper limit on the document count that can be part of the chunk for moveChunk to happen.
Based on the following code base, this looks to be 250,000 and should be reflected in the limits:
- https://github.com/mongodb/mongo/blob/master/src/mongo/s/chunk.cpp#L82
- https://github.com/mongodb/mongo/blob/master/src/mongo/s/d_migrate.cpp#L463-L501
This is mainly an issue when the user has small documents (sometimes along with low cardinality shard key) and the number of documents with same shard key exceed this limit.