Editing Write–write conflict

{{short description |Interleaved transaction conflict}}
{{Use British English |date=February 2024}}
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{{More citations needed |date=February 2024}}
In [[computer science]], in the field of [[database]]s, '''write–write conflict''', also known as '''overwriting [[commit (data management)|uncommitted]] data''' is a computational anomaly associated with interleaved execution of [[Database transaction|transactions]]. Specifically, a '''write–write conflict''' occurs when "transaction requests to write an entity for which an unclosed transaction has already made a write request."<ref name="stro81" />

Given a [[database transaction schedule|schedule]] S

<math>S = \begin{bmatrix}
T1 & T2 \\
W(A) & \\
 & W(B) \\
W(B) & \\
Com. & \\
 & W(A)\\
 & Com. \end{bmatrix}</math>

note that there is no read in this schedule. The writes are called '''''blind writes'''''.

We have a '''''dirty write'''''.<ref name="sql-isolation">
{{cite web
| url = http://www.cs.umb.edu/~poneil/iso.pdf
| title = A Critique of ANSI SQL Isolation Levels
| access-date = 29 July 2012 }}
</ref>  Any attempts to make this schedule serial would give off two different results (either T1's version of A and B is shown, or T2's version of A and B is shown), and would not be the same as the above schedule.  This schedule would not be [[Serializability|serializable]].

[[Strict two-phase locking|Strict 2PL]] overcomes this inconsistency by locking T1 out from B.  Unfortunately, [[deadlock (computer science)|deadlock]]s are something Strict 2PL does not overcome all the time.

== See also ==
* [[Concurrency control]]
* [[Read–write conflict]]
* [[Write–read conflict]]

==References==
{{reflist |refs=
<ref name="stro81">{{cite conference |title=Distributed database concurrency controls using before-values |last1=Stearns |first1=Richard E. |author1-link=Richard E. Stearns |last2=Rosenkrantz |first2=Daniel J. |year=1981 |pages=74–83 |url=https://dl.acm.org/doi/pdf/10.1145/582318.582330 |conference=1981 ACM SIGMOD International Conference on Management of Data |publisher=[[Association for Computing Machinery]] |location=New York, USA |doi=10.1145/582318.582330 |isbn=0-89791-040-0 |url-access=subscription }}</ref>
}}

{{DEFAULTSORT:Write-write conflict}}
[[Category:Data management]]
[[Category:Transaction processing]]