Data Latency

Data latency is the gap between the moment an event happens on the site and the moment that event becomes visible in the reports.

Every analytics system has this lag, because data must be collected from the browser, reach the server, be processed and aggregated, and then land in a report; the right question is not whether latency exists but how much, and for which report. There are two distinct regimes: a live view whose latency must be seconds to a few minutes or it is useless, and a historical report whose latency of minutes or even hours does no harm because nobody makes an urgent decision on this morning's data. A common mistake is to treat a small difference between the realtime number and the historical number for the same window as a bug; it is usually just processing and finalization lag, and the two figures converge after a while. The data source matters too: a report fed from an external service inherits that service's latency.