- cache usage reaches 100% and continues climbing, reaching 145% by the end of the data
- doesn't look like a long-running transaction (range of ids pinned doesn't grow)
- no problem with amount of dirty data
& checkpoints are proceeding at a regular pace, taking no more than about 10 s
- at about the point where cache usage began to climb we see lag on secondary member 3 growing (but not on secondary member 2). This suggests maybe related to
SERVER-23622, but when member 3 is restarted at D it is able to catch up quickly, and cache growth does not stop, actually appears to accelerate at that point. Not clear why it began lagging but was able to catch up quickly when it was restarted.