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From "Brandon Williams (JIRA)" <>
Subject [jira] [Commented] (CASSANDRA-4038) Investigate improving the dynamic snitch with reservoir sampling
Date Fri, 27 Jul 2012 15:20:35 GMT


Brandon Williams commented on CASSANDRA-4038:

I'm a bit concerned that shoehorning latency timings into a long from a double will always
yield zero in a healthy gigabit network where the timings are generally fractional.  But,
there's a good chance in a situation with such similar values their weight is irrelevant after
CASSANDRA-3722 anyway.

Have you done any profiling to see if this actually is cheaper than the fixed window size?
 Specifically I'm worried about receiveTiming becoming more expensive.
> Investigate improving the dynamic snitch with reservoir sampling
> ----------------------------------------------------------------
>                 Key: CASSANDRA-4038
>                 URL:
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: Brandon Williams
>            Assignee: Pavel Yaskevich
>             Fix For: 1.2
>         Attachments: CASSANDRA-4038.patch
> 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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