Database transaction

A database transaction is a unit of work performed against a database management system or similar system that is treated in a coherent and reliable way independent of other transactions. A database management system ( DBMS) is Computer software designed for the purpose of managing Databases DBMSes may use any of a variety of Data models A database transaction, by definition, must be atomic, consistent, isolated and durable. In Database systems a consistent transaction is one that does not violate any Integrity constraints during its execution In Database systems isolation is a property that defines how/when the changes made by one operation become visible to other concurrent operations In Database systems durability is the ACID property which guarantees that transactions that have committed will survive permanently These properties of database transactions are often referred to by the acronym ACID. In Computer science, ACID ( Atomicity Consistency Isolation Durability) is a set of properties that guarantee that Database transactions are

Transactions provide an "all-or-nothing" proposition stating that work units performed in a database must be completed in their entirety or take no effect whatsoever. Further, transactions must be isolated from other transactions, results must conform to existing constraints in the database and transactions that complete successfully must be committed to durable storage.

In some systems, transactions are also called LUWs for Logical Units of Work.

1 Purpose of transaction
2 Transactional databases
- 2.1 In SQL
3 Distributed transactions
4 Transactional filesystems
5 See also
6 External links

Purpose of transaction

Databases and other data stores in which the integrity of data is paramount often include the ability to handle transactions to ensure the integrity of data is maintained. A Computer Database is a structured collection of records or data that is stored in a computer system Data integrity is a term used in Computer science and Telecommunications that can mean ensuring data is "whole" or complete the condition in which data are A single transaction is composed of one or more independent units of work, each reading and/or writing information to a database or other data store. When this happens it is often important to ensure that the database or data store is left in a consistent state.

The concept of transactions are often demonstrated via double-entry accounting systems. In double-entry accounting every debit requires an associated credit be recorded. If you wrote a check for $100 to buy groceries at the local store a transactional double-entry accounting system would record the following two entries to cover the single transaction:

Debit $100 to Groceries Expense Account
Credit $100 to Checking Account

In a transactional system both entries would be made, or both entries would fail. By treating the recording of multiple entries as an atomic transactional unit of work you maintain the integrity of the data recorded. In other words, you will not end up with a situation in which a debit is recorded but no associated credit is recorded, or vice versa.

Transactional databases

Databases that support transactions are called transactional databases. Most modern relational database management systems fall into this category. A Relational database management system (RDBMS is a Database management system (DBMS that is based on the Relational model as introduced by E

In a database system a single transaction might be composed of one or more data manipulation statements and queries, each reading and/or writing information in the database. Consistency and integrity of data is considered highly important in database systems. The term database system is typically used to encapsulate the constructs of a Data model, database Management system ( DBMS) and Database. A simple transaction is usually issued to the database system in a language like SQL wrapped in a transaction, using a pattern similar to the following:

Begin the transaction
Execute several data manipulations and queries
If no errors occur then commit the transaction
If errors occur then rollback the transaction

If no errors occurred during the execution of the transaction the transaction is committed. A transaction commit operation applies all data manipulations within the scope of the transaction and persists the results to the database. If an error occurs during the transaction, or if the user specifies a rollback operation, the data manipulations within the transaction are not persisted to the database. In Database technologies a rollback is an operation which returns the database to some previous state In no case can a partial transaction be committed to the database since that would leave the database in an inconsistent state.

In SQL

A BEGIN WORK statement in SQL or, on some systems, any statement that will modify data, starts a transaction within a relational database management system (RDBMS). A Relational database management system (RDBMS is a Database management system (DBMS that is based on the Relational model as introduced by E

Any work done after this point will not be visible to other users, until a COMMIT statement is issued. In the context of Computer science and Data management, commit refers to the idea of making a set of tentative changes permanent A ROLLBACK statement can also be issued, which will undo any work performed since the BEGIN WORK command. In Database technologies a rollback is an operation which returns the database to some previous state Both COMMIT and ROLLBACK will end the transaction: another BEGIN WORK will need to be issued to start a new one.

Some database systems allow the synonyms BEGIN and BEGIN TRANSACTION, and may have other options available.

Distributed transactions

Distributed transactions are implemented as transactions against multiple applications or hosts. A distributed transaction is an Operations bundle, in which two or more network hosts are involved A distributed transaction enforces the ACID properties over multiple systems or data stores, and might include systems such as databases, file systems, messaging systems, and other applications. In a distributed transaction a coordinating service ensures that all parts of the transaction are applied to all relevant systems. As with database and other transactions, if any part of the transaction fails, the entire transaction is rolled back across all affected systems.

Transactional filesystems

The Namesys Reiser4 filesystem for Linux [1] and the newest version of the Microsoft NTFS filesystem both support transactions [2], but file system transactions are rarely used in practice due to lack of compatibility with older systems. Reiser4, named after creator Hans Reiser, is a Computer File system, a new "from scratch" successor to the ReiserFS file system Linux (commonly pronounced ˈlɪnəks NTFS (New Technology File System Is the standard File system of Windows NT, including its later versions Windows 2000, Windows XP, Windows

External links

Transaction Processing

A distributed transaction is an Operations bundle, in which two or more network hosts are involved With reference to a Database transaction, a nested transaction occurs when a new transaction is started by an instruction that is already inside an existing transaction In Computer science, ACID ( Atomicity Consistency Isolation Durability) is a set of properties that guarantee that Database transactions are In Computer science, software transactional memory (STM is a Concurrency control mechanism analogous to Database transactions for controlling access to Long-running transactions are computer Database transactions that avoid locks on non-local resources use compensation to handle failures potentially aggregate smaller For other meanings see the disambiguation page at Transaction.

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