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I have read some notes about the two but yet still confused about why there is a need for the strict 2phase locking. Based on some slides,

Two Phase Locking and Strict Two Phase Locking

They have a single difference which is :

  1. If transaction T releases any lock, it can acquire no new locks. <- 2PL
  2. Hold all locks until end of transaction. <- S2PL

I will like a practical example of a Transaction in both strict and normal.Highlighting the differences.

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There are mainly two reasons for adopting Strict 2PL rather than Basic 2PL, explained in [1].

  • The first reason is about the time when a 2PL scheduler can release some (read/write) lock owned by some transaction on some data item.

  • A second reason for the scheduler to keep a transaction’s locks until it ends, and specifically until after the DM processes the transaction’s Commit or Abort, is to guarantee a strict execution. Strict executions are recoverable and avoid cascading aborts (ACA).

[1] Chapter 3 "Two Phase Locking" in the Book "Concurrency Control and Recovery in Database Systems"; Page 59. By Bernstein et al., 1987.

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