In
computer science
Computer science is the study of computation, automation, and information. Computer science spans theoretical disciplines (such as algorithms, theory of computation, information theory, and automation) to Applied science, practical discipli ...
, in the field of
database
In computing, a database is an organized collection of data stored and accessed electronically. Small databases can be stored on a file system, while large databases are hosted on computer clusters or cloud storage. The design of databases sp ...
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
In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a sequ ...
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
deadlock
In concurrent computing, deadlock is any situation in which no member of some group of entities can proceed because each waits for another member, including itself, to take action, such as sending a message or, more commonly, releasing a lo ...
s.
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 computing, concurrent operations a ...
*
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.
Given a schedule S
:S = \begin
T1 & T2 \\
R(A) & \\
& R( ...
*
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.
Given a schedule S
S = \begin
T1 & T2 \\
W(A) & ...
References
{{DEFAULTSORT:Write-Read Conflict
Data management
Transaction processing