Documentation Request Summary:

I suggest completely removing all mentions of the old OP_MSG from this page https://docs.mongodb.com/manual/reference/mongodb-wire-protocol/, across all versions of our documentation. It will make it less confusing once https://docs.google.com/document/d/1-h7Y3E9PYyvFNP0McbfSyI4WiAtaacW84bQLnA2MvYA/ is done.

Engineering Ticket Description:

The old OP_MSG format has been deprecated since at least mongodb version 1.2 (https://github.com/mongodb/mongo/blob/v1.2/db/instance.cpp#L204) and has never worked in mongos. Clearing it out will make room for the new OP_MSG format.