In
database
In computing, a database is an organized collection of data stored and accessed electronically. Small databases can be stored on a file system, while large databases are hosted on computer clusters or cloud storage. The design of databases ...
technologies, a rollback is an operation which returns the database to some previous state. Rollbacks are important for database
integrity
Integrity is the practice of being honest and showing a consistent and uncompromising adherence to strong moral and ethical principles and values.
In ethics, integrity is regarded as the honesty and truthfulness or accuracy of one's actions. In ...
, because they mean that the database can be restored to a clean copy even after erroneous operations are performed. They are crucial for recovering from database server crashes; by rolling back any
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
transaction log
In the field of databases in computer science, a transaction log (also transaction journal, database log, binary log or audit trail) is a history of actions executed by a database management system used to guarantee ACID properties over crashes ...
, but can also be implemented via
multiversion concurrency control
Multiversion concurrency control (MCC or MVCC), is a concurrency control method commonly used by database management systems to provide concurrent access to the database and in programming languages to implement transactional memory.
Description
...
.
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,
ROLLBACK is a command that causes all data changes since the last
START TRANSACTION or
BEGIN 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.
A
ROLLBACK statement will also release any existing
savepoint
A savepoint is a way of implementing subtransactions (also known as nested transactions) within a relational database management system by indicating a point within a transaction that can be " rolled back to" without affecting any work done in ...
s that may be in use.
In most SQL dialects,
ROLLBACKs are connection specific. This means that if two connections are made to the same database, a
ROLLBACK made in one connection will not affect any other connections. This is vital for proper
concurrency.
See also
*
Savepoint
A savepoint is a way of implementing subtransactions (also known as nested transactions) within a relational database management system by indicating a point within a transaction that can be " rolled back to" without affecting any work done in ...
*
Commit
*
Undo
Undo is an interaction technique which is implemented in many computer programs. It erases the last change done to the document, reverting it to an older state. In some more advanced programs, such as graphic processing, undo will negate the las ...
*
Schema migration
Notes
References
*
"ROLLBACK Transaction" Microsoft SQL Server.
MySQL.
{{Authority control
Database theory
Transaction processing
Reversible computing