Concurrency Control

Optimistic concurrency with CAS

Head updates use compare-and-swap semantics:

UPDATE entity_head
SET head_revision_id = :new
WHERE entity_id = :id
  AND head_revision_id = :expected

If the update fails: - The client re-reads head - Recomputes next revision - Retries

This prevents: - Head regression - Lost updates - Split-brain histories

Write serialization scope

Concurrency is controlled per entity

No global locks

High-contention entities degrade locally only