Low Description
To quote the conf:
# if set greater than zero and read_repair_chance is < 1.0, this will allow # 'pinning' of replicas to hosts in order to increase cache capacity. # The badness threshold will control how much worse the pinned host has to be # before the dynamic snitch will prefer other replicas over it. This is # expressed as a double which represents a percentage. Thus, a value of # 0.2 means Cassandra would continue to prefer the static snitch values # until the pinned host was 20% worse than the fastest. dynamic_snitch_badness_threshold: 0.1
An assumption of this feature is that scores will vary by less than dynamic_snitch_badness_threshold during normal operations. Attached is the result of polling a node for the scores of 6 different endpoints at 1 Hz for 15 minutes. The endpoints to sample were chosen with `nodetool getendpoints` for row that is known to get reads. The node was acting as a coordinator for a few hundred req/second, so it should have sufficient data to work with. Other traces on a second cluster have produced similar results.
- The scores vary by far more than I would expect, as show by the difficulty of seeing anything useful in that graph.
- The difference between the best and next-best score is usually > 10% (default dynamic_snitch_badness_threshold).
Neither ClientRequest nor ColumFamily metrics showed wild changes during the data gathering period.
Attachments:
- jython script cobbled together to gather the data (based on work on the mailing list from Maki Watanabe a while back)
- csv of DES scores for 6 endpoints, polled about once a second
- Attempt at making a graph
