See http://shortn/_cUMYbNPIwg and http://shortn/_5oR17MtBpv

This is particularly visible in slow queries and CPU load. I initially thought this was an effect of readonly heartbeat, but it wasn't related to the rollout of that feature, which happened at 1:21 PM (crrev.com/i/618529), and then was rolled back briefly, from 3:33 to 3:59. Understanding this seems potentially important.