The ShardingDDLComponent infrastructure includes a state document to keep track of the progress of its execution; this object may be accessed by multiple threads, such as:

• the executor running the coordinator itself (r/w)
• $currentOps requests (r)

The DDL infrastructure also defines a mutex to protect the access to the doc, but it is still the responsibility of each implementation to enforce the right semantics.

The DDL infrastructure could instead provide a set of higher level primitives for accessing the recovery document object that implements the following semantics:

• the DDL executor thread is the only one allowed to write onto the recovery document
• no reads are allowed while a write is in progress