If the gearman server vanishes (e.g. due to a VM crash) some clients
like the merger may not notice that it is gone. They just wait forever
for data to be received on an inactive connection. In our case the VM
containing the zuul-scheduler crashed and after the restart of the
scheduler all mergers were waiting for data on the stale connection
which blocked a successful scheduler restart. Using tcp keepalive we
can detect that situation and let broken inactive connections be
killed by the kernel.