Chapter 18: Problem 2

What are some variations of the two-phase locking protocol? Why is strict or rigorous two-phase locking often preferred?

Short Answer

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There are four variations of the two-phase locking protocol: Basic, Conservative, Rigorous, and Strict two-phase locking. Each serves different needs, with unique features in how they handle transactions. Strict and rigorous two-phase locking are usually preferred as they prevent cascading rollbacks, a situation where a single transaction failure leads to multiple transaction rollbacks, as they ensure locks are held until the transaction is entirely completed.

Step by step solution

Identifying Variations of Two-Phase Locking

In concurrency control, the two-phase locking protocol (2PL) is a method that guarantees conflict-serializability. Two-phase locking has several variations which include: Basic two-phase locking, Conservative two-phase locking,Rigorous two-phase locking, Strict two-phase locking. Each comes with distinct features in tune with various needs.

Detailing Variations of Two-Phase Locking

In Basic 2PL, a transaction holds all the locks until it commits or aborts. In Conservative 2PL, a transaction locks all the data items it accesses before the transaction begins to prevent deadlock. In Rigorous 2PL, all locks held by a transaction are released when the transaction is completely finished. That is, locks are held until the commit point and released under single operation, unlike Basic 2PL where locks can be released at any time. In Strict 2PL, all locks held by a transaction are released when the transaction is completed, slightly different with Rigorous 2PL where locks are released as soon as they are no longer needed.

Understanding Preference for Strict or Rigorous Two-Phase Locking

Strict and rigorous two-phase locking are typically preferred due to their ability to prevent cascading rollbacks, which are scenarios where a single transaction failure can lead to a series of transaction rollbacks. Both Strict and Rigorous 2PL limit the possibilities of this occurring by ensuring locks are tightly controlled and held until either the transaction is completely completed.

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What are some variations of the two-phase locking protocol? Why is strict or rigorous two-phase locking often preferred?

Short Answer

Step by step solution

Identifying Variations of Two-Phase Locking

Detailing Variations of Two-Phase Locking

Understanding Preference for Strict or Rigorous Two-Phase Locking

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