The beginning of heartbeats for pessimistic locks may be too late

[ekexium]

Current process:

1. lock all keys
2. start heartbeat

Consider we lock a lot of keys in a single command, which takes a long time. Before the heartbeat begins, some of the locks may be stale and removed.

A possible improvement:

1. lock the primary key if it's not locked
2. start heartbeat
3. lock other keys