It might be useful in larger deployments to have the ability to lazily bootstrap cold tablets.
Currently, WAL replay consumes a significant amount of bootstrapping time. If we know certain tablets are read infrequently, we ought to be able to indicate that we only want to bootstrap and replay the WALs for tablets that have been accessed recently.
This patch gave us a metric for hotness and coldness at the replica level – we might want to consider aggregating this on the master to determine what partitions are hot and cold, and have the master signal to the appropriate tablet servers upon registering that certain replicas should be bootstrapped. We might also consider bootstrapping when a client first calls OpenTable().