Start with a template. Work through each step. Ask Coach when you need a second opinion.
Company tags are community-reported. Counts on cards show how many people reported that design.
The classes and code behind the ad click aggregator: signed click tokens, a redirect that never waits on the log, and a stream counter that de-duplicates and handles late clicks. Tests run all of it.
Search a billion documents in 200 ms: inverted indexes, analysers, Lucene segments, shards and replicas, query then fetch with BM25, fed by CDC.
A key-value store like DynamoDB, from one durable node to Paxos-replicated partitions to global tables run for thousands of tenants.