Description

We have discovered a flaw in mapReduce, but we don't intend on dedicating resources to it at the moment. Performing the following actions can potentially cause a crash.

1. All concurrent mapReduces to sharded output collections with the reduce option.
2. All concurrent mapReduces to sharded output collections with the replace option that output to an empty collection.
3. All concurrent mapReduces to sharded output collections with the merge option that output to an empty collection.

Scope of changes

We should indicate that those former mapReduces are unsupported.

Include general advisory to use aggregation instead of mapreduce for operations against sharded collections.

Impact to Other Docs

MVP (Work and Date)

Resources (Scope or Design Docs, Invision, etc.)