Domain relational calculus: Difference between revisions

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In [[computer science]], in the field of [[database]]s, '''Write-Read Conflict''', also known as '''reading uncommitted data''', is a computational anomaly associated with interleaved execution of transactions.
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Given a schedule S
 
:<math>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}</math>
 
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|Strict 2PL]] overcomes this inconsistency by locking T2 out from performing a Read/Write on A.  Note however that [[Strict two-phase locking|Strict 2PL]] can have a number of drawbacks, such as the possibility of [[deadlock]]s.
 
== See also ==
 
* [[Concurrency control]]
* [[Read-Write conflict]]
* [[Write-Write conflict]]
 
==References==
{{reflist}}
{{Unreferenced|date=August 2009}}
 
{{DEFAULTSORT:Write-Read Conflict}}
[[Category:Data management]]
[[Category:Transaction processing]]

Latest revision as of 12:19, 30 May 2014

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