The Great Migration from MongoDB to PostgreSQL

Original Article ↗ Hacker News Discussion ↗

State of MongoDB vs PostgreSQL and Others

  • Many commenters see PostgreSQL as the “default” general-purpose database now, with MongoDB and other NoSQL systems relegated to niches.
  • Some argue MongoDB is “on life support”; others counter with its strong revenue growth and large installed base.
  • MySQL is viewed as still widely used but technically behind Postgres; MariaDB is seen as MySQL’s spiritual continuation.

Document Databases vs Relational Databases

  • Strong view that most application data is inherently relational; using a document DB as the primary store often backfires.
  • Repeated stories of painful migrations from MongoDB/CouchDB/RethinkDB back to Postgres for relational and reporting needs.
  • A minority emphasize that document DBs have valid use cases (e.g., form wizards, replicated logs/queues, read-heavy workloads).

MongoDB: Licensing, Business Metrics, and Maturity

  • License changes are widely seen as damaging to MongoDB’s ecosystem and long‑term goodwill.
  • Debate over how to judge health: revenue growth vs large and persistent losses vs cash flow.
  • Some say MongoDB has matured (transactions, joins, better tooling), but distrust remains from earlier instability and marketing overreach.

Postgres Features and JSON Support

  • Postgres praised for robustness, rich SQL, extensions (e.g., PostGIS, FDWs), JSON/JSONB columns, and plugin ecosystem.
  • Discussion that JSON updates in Postgres rewrite the whole object, can cause race conditions, and are not field-atomic like Mongo’s operators.
  • Others argue large JSON blobs in Postgres are usually a design smell; you should model predictable structure relationally.

Scaling, HA, and Operational Issues

  • MongoDB clustering and replica sets seen as “easy out of the box.”
  • Postgres criticized for lacking native, turnkey HA/sharding; real deployments often rely on third-party tools and custom scripts.
  • Counterpoint: vertical scaling + basic replication covers 99% of real-world needs; specialized distributed SQL/NoSQL only for extreme scale.

Hype Cycles and Tool Choice

  • Many frame the NoSQL era as a hype-driven overreaction, now swinging back to relational DBs with JSON support.
  • Consensus that picking MongoDB for relational workloads, or any DB based on fashion/PR alone, leads to expensive rewrites.
  • Recurrent heuristic: “Use Postgres by default; deviate only with a very clear, scale- or workload-driven reason.”