The headline is about READ COMMITTED isolation level in PostgreSQL allowing lost updates. Let me rewrite this concisely.

Short summary

READ COMMITTED, PostgreSQL's default isolation level, prevents dirty reads but silently allows lost updates when concurrent transactions read and modify the same row. A concrete NestJS counter-increment example shows two simultaneous requests both reading 5 and writing 6 instead of 7 — no error, no deadlock, just a silently lost increment. The article clarifies that atomicity (all-or-nothing on failure) and isolation (concurrent access correctness) are separate ACID properties, and READ COMMITTED is weak on the isolation axis.

• •READ COMMITTED only prevents dirty reads — it does not prevent lost updates from concurrent read-modify-write cycles
• •Two simultaneous transactions can both read the same value and overwrite each other's changes with no error or deadlock
• •Atomicity and isolation are separate ACID properties; wrapping code in BEGIN/COMMIT does not guarantee concurrent-access safety

Generated with AI, which can make mistakes.