In
computer science
Computer science is the study of computation, information, and automation. Computer science spans Theoretical computer science, theoretical disciplines (such as algorithms, theory of computation, and information theory) to Applied science, ...
, in the field of
database
In computing, a database is an organized collection of data or a type of data store based on the use of a database management system (DBMS), the software that interacts with end users, applications, and the database itself to capture and a ...
s, 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."
Given a schedule S
:
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
An acid is a molecule or ion capable of either donating a proton (i.e. Hydron, hydrogen cation, H+), known as a Brønsted–Lowry acid–base theory, Brønsted–Lowry acid, or forming a covalent bond with an electron pair, known as a Lewis ...
rules.
Strict 2PL overcomes this inconsistency by locking T2 out from performing a Read/Write on A. Note however that
Strict 2PL can have a number of drawbacks, such as the possibility of
deadlocks.
See also
*
Concurrency control
In information technology and computer science, especially in the fields of computer programming, operating systems, multiprocessors, and databases, concurrency control ensures that correct results for concurrent operations are generated, whil ...
*
Read–write conflict
In computer science, in the field of databases, read–write conflict, also known as unrepeatable reads, is a computational anomaly associated with interleaved execution of transactions. Specifically, a read–write conflict occurs when a "trans ...
*
Write–write conflict
In computer science, in the field of databases, write–write conflict, also known as overwriting uncommitted data is a computational anomaly associated with interleaved execution of transactions. Specifically, a write–write conflict occurs ...
References
{{DEFAULTSORT:Write-Read Conflict
Data management
Transaction processing