Concurrency Control Techniques: Methods to ensure isolation and serializability when multiple transactions execute concurrently.

Techniques:

• Lock-Based: 2PL (growing/shrinking), Strict 2PL, Shared (S) and Exclusive (X) locks, prevents dirty read/write. Example: before read acquire S, before write acquire X.

• Timestamp Ordering: Assign timestamp TS(T), ensure conflict order follows timestamp via W-timestamp/R-timestamp, Thomas write rule for obsolete writes.

• Validation/Optimistic: Read phase, validation (check conflicts), write phase - no locking, abort if conflict (good for low contention).

• Multiversion (MVCC): Keep multiple versions for reads without locking, readers read snapshot.

• Granularity: Multiple granularity locks (IS, IX, SIX) for hierarchy.

Goal: Prevent anomalies: lost update, dirty read, non-repeatable read, phantom. Provide serializable schedule.