Conservative two-phase locking

In computer science, conservative two-phase locking (C2PL) is a locking method used in DBMS and relational databases. Conservative 2PL prevents deadlocks. The difference between 2PL and C2PL is that C2PL's transactions obtain all the locks they need before the transactions begin. This is to ensure that a transaction that already holds some locks will not block waiting for other locks. In heavy lock contention, C2PL reduces the time locks are held on average, relative to 2PL and Strict 2PL, because transactions that hold locks are never blocked.