D1 read replicas returned stale data for 6 seconds — here's what I measured and how I designed around it

At p99, a D1 read replica in Tokyo was 6.1 seconds behind a write that landed on the Eastern NA primary. I found this out not from the docs, but from a Korean ad-ops campaign tracker silently throttling the wrong impressions.

D1's architecture is straightforward: one SQLite primary, read replicas pushed to edge POPs, writes always hit the primary, reads go to the nearest replica. The docs acknowledge eventual consistency but give you no number to plan around. So I built a staleness probe — write a row with a UUID and epoch, poll the replica until it appears, record the delta. Across 200 probes from ap-northeast-1:

p50: ~800ms

p95: ~3,400ms

p99: ~6,100ms