Inside the Black Box: How Database INSERT Operations Really Work

This article reveals that calling INSERT triggers multiple behind-the-scenes operations that most engineers never consider. Different databases make fundamentally different architectural choices—PostgreSQL uses WAL logs and heap files, MongoDB leverages B-Trees with WiredTiger, and Cassandra employs immutable SSTables. Understanding these internal mechanisms is critical because each approach has cascading effects on write speed, read performance, crash recovery, and latency under load.