SERVER-19122 and SERVER-18983 describe two separate cases where table inserts on a MongoDB primary are done in-order on the primary but are done out-of-order on the secondary, and the result is that the secondary may not be able to keep up with the primary, apparently due to the performance difference between these cases in WT. It may be difficult to address the issue in mongod, so this ticket is to track whether the performance difference can be addressed in WT.

Stack traces seem to indicate that the primary difference is that inserts in the disordered case are delayed by evictions due to page splits, but not in the ordered case. Will attach data.