Editing Speculative execution (section)

{{short description|Computer optimization technique}}
'''Speculative execution''' is an [[optimization (computer science)|optimization]] technique where a [[computer system]] performs some task that may not be needed. Work is done before it is known whether it is actually needed, so as to prevent a delay that would have to be incurred by doing the work after it is known that it is needed. If it turns out the work was not needed after all, most changes made by the work are reverted and the results are ignored.

The objective is to provide more [[Concurrency (computer science)|concurrency]] if extra [[Resource (computer science)|resources]] are available. This approach is employed in a variety of areas, including [[branch predictor|branch prediction]] in [[instruction pipeline|pipelined]] [[CPU|processors]], value prediction for exploiting value locality, prefetching [[Instruction prefetch|memory]] and [[File system|files]], and [[optimistic concurrency control]] in [[Relational database management system|database systems]].<ref>{{Cite conference |last=Lampson |first=Butler |author-link=Butler Lampson |date=2006 |editor-last1=Momenzadeh |editor-first1=Mariam |editor-last2=Shvartsman |editor-first2=Alexander A. |title=Lazy and Speculative Execution in Computer Systems |url=https://link.springer.com/chapter/10.1007/11945529_1 |book-title=Principles of Distributed Systems |series=Lecture Notes in Computer Science |conference=10th International Conference on Principles of Distributed Systems |language=en |location=Bordeaux, France |publisher=Springer |volume=4305 |pages=1–2 |doi=10.1007/11945529_1 |isbn=978-3-540-49991-6|url-access=subscription }}</ref><ref name="DivisionRaghavan1998">{{cite conference
|last1=Raghavan
|first1=Prabhakar
|last2=Shachnai
|first2=Hadas
|last3=Yaniv
|first3=Mira
|title=Dynamic schemes for speculative execution of code
|url=https://ieeexplore.ieee.org/document/693711
|year=1998
|doi=10.1109/MASCOT.1998.693711
|book-title=Proceedings of the Sixth International Symposium on Modeling, Analysis and Simulation of Computer and Telecommunication Systems
|publisher=IEEE
|pages=309–314
|access-date=18 January 2011|url-access=subscription
}}</ref><ref>
{{cite conference
|author-link= H. T. Kung
|first= H. T. |last= Kung
|author2=John T. Robinson
|title= On optimistic methods for concurrency control
|book-title= ACM Trans. Database Syst.
|volume= 6
|number= 2
|date=June 1981
|url=https://apps.dtic.mil/dtic/tr/fulltext/u2/a081452.pdf|archive-url=https://web.archive.org/web/20190831230313/https://apps.dtic.mil/dtic/tr/fulltext/u2/a081452.pdf|url-status=live|archive-date=August 31, 2019}}</ref>

[[Speculative multithreading]] is a special case of speculative execution.