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Stefan Podkowinski commented on CASSANDRA-11547:
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bq. With this patch, we're not trying catch things at the smallest size, a la
jHiccup, but really just want to catch things after large enough time distances.
Is this how clock drift actually happens? I was assuming clocks between systems
are drifting apart slowly over time, instead of just jumping seconds forward or
back.
> Add background thread to check for clock drift
> ----------------------------------------------
>
> Key: CASSANDRA-11547
> URL: https://issues.apache.org/jira/browse/CASSANDRA-11547
> Project: Cassandra
> Issue Type: Improvement
> Components: Core
> Reporter: Jason Brown
> Assignee: Jason Brown
> Priority: Minor
> Labels: clocks, time
>
> The system clock has the potential to drift while a system is running. As a
> simple way to check if this occurs, we can run a background thread that wakes
> up every n seconds, reads the system clock, and checks to see if, indeed, n
> seconds have passed.
> * If the clock's current time is less than the last recorded time (captured n
> seconds in the past), we know the clock has jumped backward.
> * If n seconds have not elapsed, we know the system clock is running slow or
> has moved backward (by a value less than n)
> * If (n + a small offset) seconds have elapsed, we can assume we are within
> an acceptable window of clock movement. Reasons for including an offset are
> the clock checking thread might not have been scheduled on time, or garbage
> collection, and so on.
> * If the clock is greater than (n + a small offset) seconds, we can assume
> the clock jumped forward.
> In the unhappy cases, we can write a message to the log and increment some
> metric that the user's monitoring systems can trigger/alert on.
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