CQRS

Command Query Responsibility Segregation separates the write model from one or more read models optimised for queries, kept in sync by events. Reads scale independently, at the cost of eventual consistency.

Where it shows up in real systems

  • Search engine

    Documents become searchable after the next refresh, so search is eventually consistent with your primary database. Queries are CPU-heavy; add nodes and replicas for throughput, and keep the source of truth elsewhere.

    In production: Elasticsearch, OpenSearch, Apache Solr, Algolia, Meilisearch

See it break, then fix it

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