Every vendor claims they scale infinitely and have sub-millisecond latency. We map reality: CAP tradeoffs, structural limits, and real-world costs.
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Stop reading marketing copy. Start understanding architecture limits.
The biggest lie in modern software engineering is that you have "Big Data" on day one. 95% of applications will never exceed a few terabytes. PostgreSQL can handle JSON, geospatial data, and full-text search out of the box. Start relational.
Read Relational GuideIf you don't define a schema in the database, you implicitly define it in your application code. This leads to spaghetti code trying to handle 4 different versions of a user object. Document stores are for polymorphic data, not laziness.
Read Document GuideIn the presence of a network partition (P), you must choose between Consistency (C) and Availability (A). Vendor claims of "solving CAP" are usually exploiting clock sync tricks (Spanner) or redefining "consistency".
Understand CAP