Excerpts from Nejc Saje's message of 2014-09-01 07:48:46 +0000: > Hey guys, > > in Ceilometer we're using consistent hash rings to do workload > partitioning[1]. We've considered generalizing your hash ring > implementation and moving it up to oslo, but unfortunately your > implementation is not actually consistent, which is our requirement. > > Since you divide your ring into a number of equal sized partitions, > instead of hashing hosts onto the ring, when you add a new host, > an unbound amount of keys get re-mapped to different hosts (instead of > the 1/#nodes remapping guaranteed by hash ring). I've confirmed this > with the test in aforementioned patch[2].
I am just getting started with the ironic hash ring code, but this seems surprising to me. AIUI we do require some rebalancing when a conductor is removed or added (which is normal use of a CHT) but not for every host added. This is supported by the fact that we currently dont have a rebalancing routine, so I would be surprised if ironic worked at all if we required it for each host that is added. Can anyone in Ironic with a bit more experience confirm/deny this? > > If this is good enough for your use-case, great, otherwise we can get a > generalized hash ring implementation into oslo for use in both projects > or we can both use an external library[3]. > > Cheers, > Nejc > > [1] https://review.openstack.org/#/c/113549/ > [2] > https://review.openstack.org/#/c/113549/21/ceilometer/tests/test_utils.py > [3] https://pypi.python.org/pypi/hash_ring > Thanks, Greg _______________________________________________ OpenStack-dev mailing list OpenStack-dev@lists.openstack.org http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev
