advanced~5h
System Design for the Persistence Layer — Read Replicas, Sharding & CQRS
A single database instance eventually hits a real ceiling no amount of query tuning can fix — read replicas, sharding, and CQRS are the three deliberate architectural strategies for scaling a persistence layer past that point, each with a genuinely different cost and consistency tradeoff.
Learning objectives
- Choose between read replicas, sharding, and CQRS based on whether the actual bottleneck is reads, writes, or divergent access patterns.
- Explain replication lag and identify which reads have a strict read-after-write consistency requirement.
- Design a shard key that avoids a hot-shard problem for a given access pattern.
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System Design for the Persistence Layer — Read Replicas, Sharding & CQRS