Write-Read conflict

In computer science, in the field of Databases, Write-Read Conflict, also known as reading uncommitted data, is a computational anomaly associated with interleaved execution of transactions.

Given a schedule D

:D = egin{bmatrix} T1 & T2 \ R(A) & \ W(A) & \ & R(A) \ & W(A)\ & R(B) \ & W(B) \ & Com. \ R(B) & \ W(B) & \ Com. & end{bmatrix}

T2 could read a database object A, modified by T1 which hasn t committed. This is a dirty read .

T1 may write some value into A which makes the database inconsistent. It is possible that interleaved execution can expose this inconsistency and lead to inconsistent final database state, violating ACID rules.

Strict two-phase locking, overcomes this inconsistency by locking T2 out from A. Unfortunately, deadlocks is something Strict 2PL does not overcome as well.