Update from 3.0.0.beta16 to 3.1.0.beta2

If the problem is a failure to spawn, then not only do we care about RAM and swap usage, but we care about the kernel configuration. If this appears in the logs

# WARNING overcommit_memory is set to 0! Background save may fail under low memory condition. To fix this issue add 'vm.overcommit_memory = 1' to /etc/sysctl.conf and then reboot or run the command 'sysctl vm.overcommit_memory=1' for this to take effect.

then it’s worth doing as advised. See also