WE SOLVE INFINITYPostgreSQL vs MongoDB
Postgres vs MongoDB decision: ACID transactions, JSONB vs BSON, vector search, multi-tenancy, replication, cost. Production guidance for SaaS founders.
Pick PostgreSQL if…
Use Postgres for 95% of new B2B SaaS in 2026 — strong consistency, JSONB columns, pgvector for AI, row-level security for multi-tenancy.
Best for: B2B SaaS, fintech, AI/RAG apps, anything that needs joins or strong consistency.
Pick MongoDB if…
Use MongoDB when documents are deeply nested, the write pattern is append-mostly (analytics events, logs), or sharding from day 1 is a hard requirement.
Best for: Event-sourced systems, content stores with deep nesting, products that need horizontal scaling from day 1.
Across 8 criteria: PostgreSQL wins 6, MongoDB wins 2, ties 0.
| Criterion | PostgreSQL | MongoDB | Winner |
|---|---|---|---|
| ACID transactions | Strong, multi-row, multi-table | Single-document strong, multi-doc weaker | PostgreSQL |
| JSON/document storage | JSONB with GIN indexes | Native BSON | MongoDB |
| Full-text search | tsvector + pg_trgm | Atlas Search (paid) | PostgreSQL |
| Vector search | pgvector (in-DB) | Atlas Vector Search | PostgreSQL |
| Horizontal scale | Citus, Aurora Limitless | Native sharding | MongoDB |
| Managed options | RDS, Aurora, Supabase, Neon, Crunchy | Atlas (single vendor) | PostgreSQL |
| Multi-tenancy isolation | Row-level security (RLS) | App-layer + DB-per-tenant | PostgreSQL |
| License | Open-source (PostgreSQL) | SSPL (server) — restrictive | PostgreSQL |
PostgreSQL pros
- +ACID + relational + JSON in one DB
- +pgvector for AI/embeddings
- +Row-level security for multi-tenancy
- +Huge managed-options market
PostgreSQL cons
- −Vertical scaling limits without Citus
- −Sharding is harder than MongoDB
MongoDB pros
- +Native sharding for horizontal scale
- +Schema-on-read flexibility
- +Atlas product is polished
MongoDB cons
- −Atlas is the only first-class managed option
- −SSPL license is restrictive
- −Cross-document transactions are slower
Frequently asked
Can Postgres replace MongoDB?⌄
For 95% of MongoDB use cases yes — JSONB + GIN indexes give you document-shape storage with relational guarantees. For deep nested updates or extreme horizontal scale, MongoDB still wins.
Which is cheaper to run?⌄
Postgres on RDS or Aurora typically beats Atlas at similar capacity. Atlas wins when you actually need its sharding/replicaset automation.
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