Editing Rollback (data management)

{{Short description|Database operation that restores a previous state}}
In [[database]] technologies, a '''rollback''' is an operation which returns the database to some previous state. Rollbacks are important for database [[data integrity|integrity]], because they mean that the database can be restored to a clean copy even after erroneous operations are performed.<ref>{{Cite web|url=https://soaringeagle.biz/what-is-a-database-rollback/|title=Database Rollback – What and Why|date=3 November 2019|access-date=16 April 2022}}</ref> They are crucial for recovering from database server crashes; by rolling back any [[Database transaction|transaction]] which was active at the time of the crash, the database is restored to a consistent state.

The rollback feature is usually implemented with a [[Database log|transaction log]], but can also be implemented via [[multiversion concurrency control]].

==Cascading rollback==
A cascading rollback occurs in database systems when a transaction (T1) causes a failure and a rollback must be performed. Other transactions dependent on T1's actions must also be rollbacked due to T1's failure, thus causing a cascading effect. That is, one transaction's failure causes many to fail.

Practical database recovery techniques guarantee cascadeless rollback, therefore a cascading rollback is not a desirable result. Cascading rollback is scheduled by dba.

==SQL==
SQL refers to Structured Query Language, a kind of language used to access, update and manipulate database.
In [[SQL]], <code>ROLLBACK</code> is a command that causes all data changes since the last <code>START TRANSACTION</code> or <code>BEGIN</code> to be discarded by the [[relational database management systems]] (RDBMS), so that the state of the data is "rolled back" to the way it was before those changes were made.<ref>{{Cite web|url=https://www.sqlshack.com/rollback-sql-rolling-back-transactions-via-the-rollback-sql-query/|title=Rollback SQL: Rolling back transactions via the ROLLBACK SQL query|author=Ben Richardson|date=26 December 2019|access-date=16 April 2022}}</ref>

A <code>ROLLBACK</code> statement will also release any existing [[savepoint]]s that may be in use.

In most SQL dialects, <code>ROLLBACK</code>s are connection specific.  This means that if two connections are made to the same database, a <code>ROLLBACK</code> made in one connection will not affect any other connections.  This is vital for proper [[Concurrent programming|concurrency]].

==Usage outside databases==
Rollbacks are not exclusive to databases: any [[stateful]] [[distributed system]] may use rollback operations to maintain [[Consistency (database systems)|consistency]]. Examples of distributed systems that can support rollbacks include [[message queue]]s and [[workflow management system]]s. More generally, any operation that resets a system to its previous state before another operation or series of operations can be viewed as a rollback.

==See also==
*[[Savepoint]]
*[[Commit (data management)|Commit]]
*[[Undo]]
*[[Schema migration]]

==Notes==
{{Reflist}}

==References==
*{{cite book |author = Ramez Elmasri |author-link = Ramez Elmasri |title= Fundamentals of Database Systems |publisher= [[Pearson Addison Wesley]] |year= 2007|isbn= 978-0-321-36957-4 }}
*[http://msdn2.microsoft.com/en-us/library/ms181299.aspx "ROLLBACK Transaction"], Microsoft SQL Server.
*[https://www.pantz.org/software/mysql/mysqlcommands.html "Sql Commands"], MySQL.

{{Databases}}
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[[Category:Database theory]]
[[Category:Transaction processing]]
[[Category:Reversible computing]]
[[Category:Database management systems]]