Lock Managers, Two-Phase Locking, and Optimistic Concurrency Control: Intention Locks, Lock Escalation, Wait-For Graphs, Silo's OCC, and Serializable Snapshot Isolation (SSI)

Deep End Era. Engineering with Sankalp · Oct 29, 2026 · 1h 15m

Two concurrent margin withdrawal requests at a London clearing house each verify that a client has two million pounds across two sub-accounts, each withdraws one point five million pounds from a different sub-account, and both commit under Snapshot Isolation—leaving the client a million pounds underwater without ever touching the same row. To understand why Snapshot Isolation allowed that bug, why classic Two-Phase Locking would have prevented it at the cost of blocking and deadlocks, and how Silo's OCC and PostgreSQL's Serializable Snapshot Isolation achieve true serializability at scale, we…