[jira] [Resolved] (KUDU-3048) Add time/clock synchronization metrics

["Alexey Serbin (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/KUDU-3048?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Alexey Serbin resolved KUDU-3048.
---------------------------------
    Fix Version/s: 1.12.0
       Resolution: Fixed

> Add time/clock synchronization metrics
> --------------------------------------
>
>                 Key: KUDU-3048
>                 URL: https://issues.apache.org/jira/browse/KUDU-3048
>             Project: Kudu
>          Issue Type: Improvement
>          Components: clock, master, tserver
>            Reporter: Alexey Serbin
>            Assignee: Alexey Serbin
>            Priority: Major
>              Labels: clock
>             Fix For: 1.12.0
>
>
> For better visibility, it would be great to add metrics reflecting time/clock synchronization parameters:
> * the stats on the max_error sampled while reading the underlying clock
> * the stats on time intervals when the underlying clock was extrapolated instead of using the actual readings: number of such intervals and stats on the interval duration
> * whether hybrid clock timestamps are generated using interpolated clock readings instead of real ones
> * if using the {{built-in}} time source:
> ** difference between tracked true time and local wallclock
> ** most recently computed true time
> ** the stats on the maximum error of the computed true time
> As for the rationale behind the new metrics:
> * max_error shows how far the clock is from the true time, and maybe it's time to use other set of NTP servers or instead increase the {{\-\-max_clock_sync_error_usec}} flag value
> * presence of the extrapolation intervals for the hybrid clock signals about periods of non-availability for NTP servers, and possible action would be re-visiting the set of NTP servers
> * if hybrid timestamps are being extrapolated for some time, Kudu masters and tablet servers might crash if the clock errors eventually goes beyond the configured threshold: it's time to start troubleshooting the issue to avoid possible non-availability of the cluster
> * the delta between true time tracked by the built-in NTP client and the local system clock is useful to understand how the log timestamps are related to the HybridClock timestamps (in case of using the built-in NTP client those might diverge)
> * the stats on true time computed by the built-in NTP client give insights on the quality of the reference NTP servers
> The new metrics can be used for monitoring and alerting, allowing for pro-active maintenance of a Kudu cluster.



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