Know the freshness vocabulary
Recall the core terms used to discuss real-time data freshness and finality.
Clock check EIP What are the three clocks in many streaming systems? Recall the clocks before flipping. Freshness What does freshness measure? The age of the data when a user or system relies on it. Freshness is usually measured as visible_at minus event_time or accepted_at, depending on the promise. Stale vs slow Is a stale metric the same as a slow dashboard? Different clocks, different fixes. Watermark What does a watermark communicate? An estimate of event-time progress: the system believes earlier events have mostly arrived. Watermarks allow windows to emit results despite out-of-order events. Finality Why did yesterday's "real-time" number…
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