Howard:
The method you describe is perfect. You can kill the client at any
time. Whatever block it was working on will be reassigned to you or
to another client. Killing the client soon after a new keyspace
begins means few wasted cycles on your machine.
To elaborate on a previous response you received...
Currently, unreturned keyspaces expire and are reassigned when I
rotate the logs. I have been rotating the logs about 2 hours after
midnight, and expiring all unreturned keys issued during the
previous midnight-to-midnight period. The shortest time before
a key expires is thus about 2 hours. The longest time is about
26 hours. As the load on the server increases, I will probably
start rotating the logs more than once per day, and I will try
to get a more uniform sliding timeout period of (say) 6 hours.
-- Rocke