NOTE
Read/Write Separation Architecture
Separating write authority from read replicas/projections and handling replication lag, read-your-writes, routing, and failover.
This is a historical learning note and may contain outdated or incomplete understanding.
Read/write separation sends mutations to an authoritative writer while reads can be served from replicas or derived read models to scale/query independently.
Asynchronous replication introduces lag: a just-committed write may not be visible on a replica. Products needing read-your-writes must route, wait on a replication position/version, or otherwise provide a consistency mechanism rather than sleep for a fixed time.
Plan failover/promotion, stale reads, cache interaction, and how clients discover the current write/read topology.