Mongodb replication applies writes in batches with a process that looks something like the following to go from timepoint A to B:

1. Block out all readers
2. Commit a write that indicates that we are invalid and that we must reach B before becoming valid
3. Divide the writes in the batch to many threads. Each thread does its writes in arbitrary order in multiple WT commits.
4. Commit a write that marks the data as valid
5. Unblock readers

One downside to this approach is that if a server is killed at a random time, the probability of the wt log replaying to a point that is invalid is high on a system with a high throughput of writes. This is made worse by SERVER-24223.

It would be helpful if we could indicate to WT somehow when we are in a valid state, such that on startup, following log-replay we would always be valid. One (suboptimal) solution would be to create a named checkpoint with a fixed name at each valid point and roll back to that snapshot on startup.