Non-strict two-phase locking

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In computer science, non-strict two-phase locking, also 2PL, is a locking method used in concurrent systems.

The rules for 2PL are similar to those of Strict 2PL:

  1. If a transaction T wants to read/write an object, it must request a shared/exclusive lock on the object.
  2. A transaction cannot request additional locks on any object once it releases any lock, and it can release locks at any time (not only at commit time as in Strict 2PL).

So, every transaction has a growing phase (it acquires locks) and a shrinking phase (it releases locks). 2PL allows only conflict serializable schedules.

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