PostgreSQL as the reliable truth store. MongoDB for document-oriented workloads. Redis for caching and session management.

ElasticSearch sat behind the NLP-backed search built at Publicis Sapient, paired with Google Dialogflow, and behind a recommendation system fed from MongoDB through Node.js. Couchbase came with the Marriott engagement. Supabase is the side-project default when a project needs a database and not a database team.

Data has structure whether or not you model it. Choosing where that structure lives — the schema, the index, or the application code — is most of the design.