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https://issues.apache.org/jira/browse/KUDU-2939?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Alexey Serbin updated KUDU-2939:
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Parent: KUDU-2935
Issue Type: Sub-task (was: Bug)
> built-in NTP client: implement stricter source selection algorithm
> ------------------------------------------------------------------
>
> Key: KUDU-2939
> URL: https://issues.apache.org/jira/browse/KUDU-2939
> Project: Kudu
> Issue Type: Sub-task
> Reporter: Alexey Serbin
> Priority: Major
>
> In the initial implementation, the built-in NTP client has a simplified NTP
> source selection/filterting algorithm: basically, it's about sanitisation of
> incoming NTP packets and ignoring falsetickers. It's necessary to make the
> source selection algorithm more robust.
> At least, it's necessary to filter out NTP servers with higher than allowed
> root distance and jitter.
> Also, as a part evaluation of the quality of a source (i.e. NTP server) in
> the source selection algorithm, it's necessary to introduce corresponding
> knobs (via gflags) to set the thresholds for the following properties of a
> source:
> * Maximum distance of a source (i.e. NTP server) from the root. The distance
> also includes the accumulated dispersion. Servers which are no longer
> synchronized might get their root distance grow high, and having this
> threshold is a way to avoid synchronising with servers which have contacted
> their own servers too long ago. By default, the maximum root distance should
> be set to 3 seconds (in the initial implementation, it's 16 seconds -- the
> maximum allowed by the RFC itself).
> * Maximum jitter (i.e. standard deviation) of time samples. This should
> prevent synchronisation with sources that have a small root distance, but
> their time is too variable. By default, this should be set to 1 second.
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