Details
Major Description
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.