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Posted to commits@cassandra.apache.org by "Benjamin Lerer (Jira)" <ji...@apache.org> on 2021/07/15 08:51:00 UTC
[jira] [Updated] (CASSANDRA-13577) Fix dynamic endpoint snitch for
sub-millisecond use case
[ https://issues.apache.org/jira/browse/CASSANDRA-13577?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Benjamin Lerer updated CASSANDRA-13577:
---------------------------------------
Status: Open (was: Patch Available)
> Fix dynamic endpoint snitch for sub-millisecond use case
> --------------------------------------------------------
>
> Key: CASSANDRA-13577
> URL: https://issues.apache.org/jira/browse/CASSANDRA-13577
> Project: Cassandra
> Issue Type: Bug
> Components: Legacy/Streaming and Messaging
> Reporter: Simon Zhou
> Assignee: Simon Zhou
> Priority: Normal
> Fix For: 3.0.x
>
>
> This is a follow up of https://issues.apache.org/jira/browse/CASSANDRA-6908. After disabling severity (CASSANDRA-11737/CASSANDRA-11738) in a few production clusters, I observed that the scores for all the endpoints are mostly 0.0. Through debugging, I found this is caused by that these clusters have p50 latency well below 1ms and the network latency is also <0.1ms (round trip). Be noted that we use p50 sampled read latency and millisecond as time unit. That means, if the latency is mostly below 1ms, the score will be 0. This is definitely not something we want. To make DES work for these sub-millisecond use cases, we should change the timeunit to at least microsecond, or even nanosecond. I'll provide a patch soon.
> Evidence of the p50 latency:
> {code}
> nodetool tablehistograms <keyspace> <table>
> Percentile SSTables Write Latency Read Latency Partition Size Cell Count
> (micros) (micros) (bytes)
> 50% 2.00 35.43 454.83 20501 3
> 75% 2.00 42.51 654.95 29521 3
> 95% 3.00 182.79 943.13 61214 3
> 98% 4.00 263.21 1131.75 73457 3
> 99% 4.00 315.85 1358.10 88148 3
> Min 0.00 9.89 11.87 61 3
> Max 5.00 654.95 129557.75 943127 3
> {code}
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