Today’s Reminders
• Sign up for Interim Project Report slots (11/20)
Concurrency Control and Recovery
Phil Gibbons
15-712 F15
Lecture 20
2
Concurrency Control and Recovery ACID Properties [Computer Science & Engineering Handbook 1997] • Atomicity: all-or-nothing
• Consistency: preserves integrity constraints • Mike Franklin (UC Berkeley) • Isolation: as-if running alone – ACM Fellow
– Sigmod Test-of-Time award 2004 & 2013 • Durability: effects of committed transactions survive failures
3 4 Serializability Concurrency Control
• Equivalent to some serial schedule • Two-phase Locking: Each transaction acquires all its locks (i.e., a one transaction at-a-time schedule) before releasing any – Conflict serializability: Preserves order of conflicting operations – Guarantees serializability in non-aborting transactions – OCC not used because consumes more resources than locking – View serializability: Preserves semantics of operations in non- aborting transactions • Deadlock avoidance/detection – Avoidance: Impose order on locks