Nested transaction

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A nested transaction is a database transaction that is started by an instruction within the scope of an already started transaction.

A transaction symbolizes a unit of work performed within a database management system against a database, and treated in a coherent and reliable way independent of other transactions. A transaction generally represents any change in a database. Transactions in a database environment have two main purposes:

  1. To provide reliable units of work that allow correct recovery from failures and keep a database consistent even in cases of system failure, when execution stops and many operations upon a database remain uncompleted, with unclear status.
  2. To provide isolation between programs accessing a database concurrently. If this isolation is not provided, the programs' outcomes are possibly erroneous.

Nested transactions are implemented differently in different databases. However, they have in common that the changes are not made visible to any unrelated transactions until the outermost transaction has committed. This means that a commit in an inner transaction does not necessarily persist updates to the database.

In some databases, changes made by the nested transaction are not seen by the 'host' transaction until the nested transaction is committed. According to some,[ who? ] this follows from the isolation property of transactions.

The capability to handle nested transactions properly is a prerequisite for true component-based application architectures. In a component-based encapsulated architecture, nested transactions can occur without the programmer knowing it. A component function may or may not contain a database transaction (this is the encapsulated secret of the component. See Information hiding). If a call to such a component function is made inside a BEGIN - COMMIT bracket, nested transactions occur. Since popular databases like MySQL [1] do not allow nesting BEGIN - COMMIT brackets, a framework or a transaction monitor is needed to handle this. When we speak about nested transactions, it should be made clear that this feature is DBMS dependent and is not available for all databases.

In computer science, information hiding is the principle of segregation of the design decisions in a computer program that are most likely to change, thus protecting other parts of the program from extensive modification if the design decision is changed. The protection involves providing a stable interface which protects the remainder of the program from the implementation.

MySQL SQL database engine software

MySQL is an open-source relational database management system (RDBMS). Its name is a combination of "My", the name of co-founder Michael Widenius's daughter, and "SQL", the abbreviation for Structured Query Language.

Theory for nested transactions is similar to the theory for flat transactions. [2]

The banking industry usually processes financial transactions using open nested transactions,[ citation needed ] which is a looser variant of the nested transaction model that provides higher performance while accepting the accompanying trade-offs of inconsistency. [3]

Further reading

International Standard Book Number Unique numeric book identifier

The International Standard Book Number (ISBN) is a numeric commercial book identifier which is intended to be unique. Publishers purchase ISBNs from an affiliate of the International ISBN Agency.

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References

  1. ↑ "Statements That Cause an Implicit Commit". MySQL 4.1 Reference Manual. Oracle. Retrieved 5 December 2010.
  2. ↑ Resende, R.F.; El Abbadi, A. (1994-05-25). "On the serializability theorem for nested transactions". Information Processing Letters. 50 (4): 177–183. CiteSeerX   10.1.1.43.6470 . doi:10.1016/0020-0190(94)00033-6.
  3. ↑ Weikum, Gerhard; Hans-J. Schek (1992). Concepts and Applications of Multilevel Transactions and Open Nested Transactions. Database Transaction Models for Advanced Applications. Morgan Kaufmann. pp. 515–553. CiteSeerX   10.1.1.17.7962 . ISBN   978-1-55860-214-4.
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