shardCollection is currently generating an op entry just after committing its metadata into the sharding catalog - and in order to guarantee at-least-once-delivery semantics, also in case of early exits after a stepdown event (1, 2).

Nevertheless, the current properties of the DDL do not guarantee that the timestamp of the op entry will always predate the time of the first user write within the sharded collection.

To overcome these inaccuracies, the commit may be described on the oplog through a 2-phase protocol.