Sharding & partitioning Study Portal

Key takeaways

• Shard for write throughput and storage; scale reads with replicas and caches first.
• Hash for even spread, range for scans, directory for flexible placement.
• Never hash mod N if N will change: consistent hashing with virtual nodes, or many fixed partitions.
• Shard key = the field most queries filter on, with high cardinality and even load.
• Hot keys: cache, replicate, split with suffixes, or isolate.
• Resharding: copy, catch up, fence and cut over, verify, clean up.
• Cross-shard queries: avoid by key choice, else scatter-gather, global indexes or denormalised copies.