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Posted to commits@cassandra.apache.org by "Pavel Yaskevich (JIRA)" <ji...@apache.org> on 2012/07/13 13:32:35 UTC
[jira] [Commented] (CASSANDRA-4038) Investigate improving the
dynamic snitch with reservoir sampling
[ https://issues.apache.org/jira/browse/CASSANDRA-4038?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13413662#comment-13413662 ]
Pavel Yaskevich commented on CASSANDRA-4038:
--------------------------------------------
I think it's worth pursuing as that would remove the work we are doing now by restricting sampling to window size and number of updates in the interval, calculating age of each response arrival, as well as improve sampling by moving to exponential decay function. There is already implementation available by Apache 2.0 License https://github.com/codahale/metrics/blob/master/metrics-core/src/main/java/com/yammer/metrics/stats/ExponentiallyDecayingSample.java
> Investigate improving the dynamic snitch with reservoir sampling
> ----------------------------------------------------------------
>
> Key: CASSANDRA-4038
> URL: https://issues.apache.org/jira/browse/CASSANDRA-4038
> Project: Cassandra
> Issue Type: Improvement
> Components: Core
> Reporter: Brandon Williams
> Assignee: Pavel Yaskevich
> Fix For: 1.2
>
>
> Dsnitch's UPDATES_PER_INTERVAL and WINDOW_SIZE are chosen somewhat arbitrarily. A better fit may be something similar to Metric's ExponentiallyDecayingSample, where more recent information is weighted heavier than past information, and reservoir sampling would also be an efficient way of keeping a statistically significant sample rather than refusing updates after UPDATES_PER_INTERVAL and only keeping WINDOW_SIZE amount.
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