On-callHardoc-g209

Subject Clock skewLevel Senior–Staff~40 minCommon in Databases & SQL interviewsIndustries Technology, Software development

Question

You run Cassandra with last-write-wins conflict resolution. Users report that occasionally an edit they JUST made reverts to an older value seconds later. Dashboards: writes for a given key go to coordinators in two different racks; one rack's nodes are ~120ms ahead on wall clock (NTP offset alert firing on 3 hosts since a maintenance window); the older value is 'winning' over the newer edit. No app deploy. How do you triage and mitigate?

What a strong answer looks like

Stop the bleeding first (mitigate), then form hypotheses from real signals. Separate root cause from symptom, communicate status as you go, and close with what prevents a repeat.

Learn the concepts

Diagram & narrate the incident

Loading whiteboard…

Run or narrate your approach, then ask the coach.