Write–read conflict

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In computer science, in the field of databases, write–read conflict (also known as reading uncommitted data and dirty read), is a computational anomaly associated with interleaved execution of transactions. Specifically, a write–read conflict occurs when "a transaction requests to write an entity, for which an unclosed transaction has already made a read request."^[1]

Given a schedule S

${\displaystyle S={\begin{bmatrix}T1&T2\\R(A)&\\W(A)&\\&R(A)\\&W(A)\\&R(B)\\&W(B)\\&Com.\\R(B)&\\W(B)&\\Com.&\end{bmatrix}}}$

T2 could read a database object A, modified by T1 which hasn't committed. This is a dirty or inconsistent 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 an inconsistent final database state, violating ACID rules.

• Concurrency control
• Read–write conflict
• Write–write conflict