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https://issues.apache.org/jira/browse/CASSANDRA-14252?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16382756#comment-16382756
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Simon Zhou commented on CASSANDRA-14252:
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Talked with [~dikanggu] offline. Previously I thought that timeout wouldn't be
counted as part of latency score. Actually it is, so setting replica score as 0
by default is less of a problem but only exposes a small vulnerability window:
Say if you have multiple replicas in a remote data center and you don't have
score for one of them, thus it will be assigned score 0. This might cause
traffic burst on this replica, for a short period of time and most of time it
won't even be noticed.
This can be mitigated by assigning a larger score (such as maximum score of all
the replicas) to the replica with null score. I'd defer this decision to
[~dikanggu]. Otherwise the patch looks good to me.
> Use zero as default score in DynamicEndpointSnitch
> --------------------------------------------------
>
> Key: CASSANDRA-14252
> URL: https://issues.apache.org/jira/browse/CASSANDRA-14252
> Project: Cassandra
> Issue Type: Bug
> Components: Coordination
> Reporter: Dikang Gu
> Assignee: Dikang Gu
> Priority: Major
> Fix For: 4.0, 3.0.17, 3.11.3
>
>
> The problem I want to solve is that I found in our deployment, one slow but
> alive data node can slow down the whole cluster, even caused timeout of our
> requests.
> We are using DynamicEndpointSnitch, with badness_threshold 0.1. I expect the
> DynamicEndpointSnitch switch to sortByProximityWithScore, if local data node
> latency is too high.
> I added some debug log, and figured out that in a lot of cases, the score
> from remote data node was not populated, so the fallback to
> sortByProximityWithScore never happened. That's why a single slow data node,
> can cause huge problems to the whole cluster.
> In this jira, I'd like to use zero as default score, so that we will get a
> chance to try remote data node, if local one is slow.
> I tested it in our test cluster, it improved the client latency in single
> slow data node case significantly.
> I flag this as a Bug, because it caused problems to our use cases multiple
> times.
> ==== logs ===
> _2018-02-21_23:08:57.54145 WARN 23:08:57 [RPC-Thread:978]:
> sortByProximityWithBadness: after sorting by proximity, addresses order
> change to [ip1, ip2], with scores [1.0]_
> _2018-02-21_23:08:57.54319 WARN 23:08:57 [RPC-Thread:967]:
> sortByProximityWithBadness: after sorting by proximity, addresses order
> change to [ip1, ip2], with scores [0.0]_
> _2018-02-21_23:08:57.55111 WARN 23:08:57 [RPC-Thread:453]:
> sortByProximityWithBadness: after sorting by proximity, addresses order
> change to [ip1, ip2], with scores [1.0]_
> _2018-02-21_23:08:57.55687 WARN 23:08:57 [RPC-Thread:753]:
> sortByProximityWithBadness: after sorting by proximity, addresses order
> change to [ip1, ip2], with scores [1.0]_
>
>
>
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