Database Management Systems · Transactions and concurrency

Lock-based concurrency control

Transactions acquiring then releasing locks on data, in two strict phases, to enforce serializability in practice.

Also known as: two-phase locking, 2PL.

Start a lesson on Lock-based concurrency control

Learn first

• Conflict-serializability: Checking whether an interleaved schedule of transactions could have happened in some one-at-a-time order instead.

Leads to

• Deadlock detection and prevention: Two transactions each waiting on a lock the other holds, and how the database detects or prevents that standoff.
• ARIES recovery algorithm: The specific three-phase algorithm (analysis, redo, undo) real databases use to recover using the write-ahead log.

Related topics

• Deadlock detection and prevention: Two transactions each waiting on a lock the other holds, and how the database detects or prevents that standoff.
• Isolation levels: How much of those concurrency anomalies a database is willing to allow, chosen as a tradeoff against speed.