Optimistic concurrency control

A database-transaction-processing technique, named and formalized by H.T. Kung and John T. Robinson in their 1981 ACM Transactions on Database Systems paper "On Optimistic Methods for Concurrency Control." Transactions run through a read phase (working on local copies of the data) and a validation phase; a transaction commits only if validation finds no conflicting concurrent transaction, and if it does, the transaction is aborted and restarted rather than blocked up front. "Optimistic" names the bet the method makes — that conflicts will usually not occur — not an optimism about outcomes once one does.

Matters to this vault as the formal ancestor of "optimistic locking," a term now used loosely enough that it gets paired, inaccurately, with check-then-act security races it was never built to fix (claim-occ-kung-robinson-1981-detects-conflicts-after-the-fact). OCC is the database field's own answer to the "lost update" anomaly (claim-lost-update-p4-distinct-from-toctou), a detect-after-the-fact, abort-and-restart discipline — distinct in both lineage and mechanism from the TOCTOU-mitigation tradition's preference for pre-emptive locking (claim-cwe-367-362-prescribe-atomicity-locking-not-occ-or-event-sourcing).

References

• claim-occ-kung-robinson-1981-detects-conflicts-after-the-fact
• claim-lost-update-p4-distinct-from-toctou
• claim-cwe-367-362-prescribe-atomicity-locking-not-occ-or-event-sourcing
• claim-no-primary-source-prescribes-occ-event-sourcing-for-sweep-vs-write-toctou