BACKUP runs a number of read commands in the past, each spanning the entire keyrange for a range. It seems to completely block any writes on the replicas executing those commands. I asked @spencerkimball if the command queue would let a write with a higher timestamp through when a long-running read command for an entire keyrange was running and he said it's possible that it doesn't. Can someone look into this?

cc @bdarnell @petermattis