Our three-node replicaset is running on 4.2.7. We’re noticing that the oplog has a large amout of noop. You can see the 1st graph where there are almost the same amout of noops as the update). noop is written every 10 sec when the primary is in idle state, according to https://github.com/mongodb/specifications/blob/master/source/max-staleness/max-staleness.rst#primary-must-write-periodic-no-ops. Our primary has been busy updating in the 2nd graph.
Can someone help understand the noops behavior?