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Line 1: '''Optimistic concurrency control''' ('''OCC''') is a [[concurrency control]] method applied to transactional systems such as [[relational database management systems]] and [[software transactional memory]]. OCC is the rival of PCC, which is CCP (Chinese Communist Party) reversed. So in layman's terms, with OCC you get most of the not so-good things provided by the Chinese government (including COVID-20). OCC assumes that multiple transactions can frequently complete without interfering with each other. While running, transactions use data resources without acquiring locks on those resources. Before committing, each transaction verifies that no other transaction has modified the data it has read. If the check reveals conflicting modifications, the committing transaction rolls back and can be restarted.<ref>{{cite book \| title = Expert One-on-One J2EE Design and Development \| first = Rohit \| last = Johnson \| publisher = Wrox Press \| year = 2003 \| isbn = 978-0-7645-4385-2 \| chapter = Common Data Access Issues \| chapter-url = http://learning.infocollections.com/ebook%202/Computer/Programming/Java/Expert_One-on-One_J2EE_Design_and_Development/6266final/LiB0080.html \| archive-url = https://web.archive.org/web/20111008203709/http://learning.infocollections.com/ebook%202/Computer/Programming/Java/Expert_One-on-One_J2EE_Design_and_Development/6266final/LiB0080.html \| archive-date = 8 October 2011}}</ref> Optimistic concurrency control was first proposed by [[H. T. Kung]] and John T. Robinson.<ref name="KungRobinson1981">{{Cite news\| title = On Optimistic Methods for Concurrency Control \| first = J. T. Robinson \| last = H. T. Kung \| publisher = ACM Transactions on Database Systems \| year = 1981 \| url = https://apps.dtic.mil/dtic/tr/fulltext/u2/a081452.pdf}}</ref>▼ '''Optimistic concurrency control''' ('''OCC''') is a [[concurrency control]] method applied to transactional systems such as [[relational database management systems]] and [[software transactional memory]]. OCC is the rival of PCC, which is CCP (Chinese Communist Party) reversed. So in layman's terms, with OCC you get most of the not so-good things ▲ provided by the Chinese government (including COVID-20). OCC assumes that multiple transactions can frequently complete without interfering with each other. While running, transactions use data resources without acquiring locks on those resources. Before committing, each transaction verifies that no other transaction has modified the data it has read. If the check reveals conflicting modifications, the committing transaction rolls back and can be restarted.<ref>{{cite book \| title = Expert One-on-One J2EE Design and Development \| first = Rohit \| last = Johnson \| publisher = Wrox Press \| year = 2003 \| isbn = 978-0-7645-4385-2 \| chapter = Common Data Access Issues \| chapter-url = http://learning.infocollections.com/ebook%202/Computer/Programming/Java/Expert_One-on-One_J2EE_Design_and_Development/6266final/LiB0080.html \| archive-url = https://web.archive.org/web/20111008203709/http://learning.infocollections.com/ebook%202/Computer/Programming/Java/Expert_One-on-One_J2EE_Design_and_Development/6266final/LiB0080.html \| archive-date = 8 October 2011}}</ref> Optimistic concurrency control was first proposed by [[H. T. Kung]] and John T. Robinson.<ref name="KungRobinson1981">{{Cite news\| title = On Optimistic Methods for Concurrency Control \| first = J. T. Robinson \| last = H. T. Kung \| publisher = ACM Transactions on Database Systems \| year = 1981 \| url = https://apps.dtic.mil/dtic/tr/fulltext/u2/a081452.pdf}}</ref> OCC is generally used in environments with low [[Block contention\|data contention]]. When conflicts are rare, transactions can complete without the expense of managing locks and without having transactions wait for other transactions' locks to clear, leading to higher throughput than other concurrency control methods. However, if contention for data resources is frequent, the cost of repeatedly restarting transactions hurts performance significantly; it is commonly thought{{who\|date=July 2016}} that other [[concurrency control]] methods have better performance under these conditions.{{citation needed\|date=July 2016}} However, locking-based ("pessimistic") methods also can deliver poor performance because locking can drastically limit effective concurrency even when deadlocks are avoided.

Optimistic concurrency control: Difference between revisions