Scaling & Sharding Study Portal

Key takeaways

• Replication scales reads and provides failover; only sharding scales writes.
• Async replication means read-your-own-writes anomalies. Route post-write reads to the primary or track the log position.
• The shard key is effectively permanent. Derive it from access patterns and atomicity needs, not from even distribution alone.
• hash % N remaps almost everything when N changes; consistent hashing limits it to 1/N.
• Virtual nodes are what make consistent hashing distribute evenly and allow weighting.
• Even row counts do not imply even load. Measure operations per shard.
• Prefer choosing a key that avoids cross-shard transactions over implementing them.