Design a secondary-index service for a sharded primary key-value store (sharded by user_id) that must answer…

Question

Design a secondary-index service for a sharded primary key-value store (sharded by user_id) that must answer queries by non-key attributes — 'all orders with status=PENDING' or 'all orders in region=EU' — across 200 shards at 60k index reads/sec. The base table takes 40k writes/sec. How do you build and maintain global secondary indexes, and how consistent are they with the base data?

Prep Room · Answer

Querying by a non-key attribute against a store sharded by user_id means a scatter-gather across all 200 shards, which won't hold up at 60k index reads/sec, so…

Secondary index service