Database transaction

Transaction in Database ( With basic introduction) - YouTube

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A transaction denotes a work unit performed in a database management system (or similar system) to the database, and is treated in a coherent and reliable manner independent of other transactions. A transaction generally represents any change in a database. Transactions in a database environment have two main goals:

To provide a reliable work unit that allows the correct recovery of failures and keep the database consistent even in case of system failure, when execution stops (completely or partially) and many operations on the database remain incomplete, with unclear status.
To provide isolation between programs that access the database simultaneously. If this isolation is not provided, the program results may be incorrect.

Database transactions, by definition, must be atomic, consistent, isolated, and durable. Database practitioners often refer to this property from database transactions using ACID acronyms.

The transaction provides an "all-or-nothing" proposition, stating that each work unit performed in the database must be completely complete or has no effect whatsoever. Furthermore, the system must isolate each transaction from another transaction, the results must conform to the restrictions contained in the database, and completed transactions must be written for long-lasting storage.

Video Database transaction

Destination

Databases and other data storage that treat data integrity as the most important often include the ability to handle transactions to maintain data integrity. One transaction consists of one or more independent work units, each reading and/or writing information to a database or other data storage. When this happens, it is often important to ensure that all processes leave databases or data storage in a consistent state.

An example of a double-entry accounting system often describes the concept of a transaction. In double-entry accounting each debit requires the recording of related credit. If someone writes a check for $ 100 to buy groceries, the transactional double-entry accounting system should record the following two entries to cover one transaction:

Debit $ 100 to Groceries Spending Account
$ 100 Credits for Checking Accounts

The transactional system will make both entries pass or both entries will fail. By treating the recording of multiple entries as an atomic transaction work unit, the system maintains the integrity of the recorded data. In other words, nothing ends in a situation where the debit is recorded but no related credit is recorded, or vice versa.

Maps Database transaction

Transactional database

A transactional database is the DBMS which provides the ACID properties for the set of bracketed (begin-commit) database operations. All transactions written in a transaction have an all or nothing effect, that is, whether the transaction is successful and all updates are in effect, or vice versa, the database is taken to a state that does not include any updates from the transaction. Transactions are also cautious that the effects of concurrent transactions meet certain guarantees known as isolation levels. The highest isolation level is serializability which ensures that the effects of concurrent transactions are equivalent to serial execution (ie sequentially) from them.

Most modern relational database management systems fall into the category of databases that support transactions. New categories of data storage known as NoSQL data stores have emerged over the last decade. NoSQL data stores pursue scalability and due to the lack of scalable solutions for transactional processing, they leave to provide transactions and therefore to ensure data consistency in the emergence of updates and concurrent access.

In database systems, transactions may consist of one or more data manipulation statements and queries, each reading and/or writing information in a database. The user of the database system considers the consistency and integrity of the data very important. Simple transactions are usually issued to the database system in a language like SQL wrapped in a transaction, using a pattern similar to the following:

Start transaction
Runs a set of data manipulation and/or queries
If no errors occur, please do transaction and end
If an error occurs, roll back the transaction and end

If no errors occur during the execution of the transaction then the system transacts. The transaction commit operation implements all data manipulation within the scope of the transaction and proceeds the result to the database. If an error occurs during a transaction, or if the user specifies a rollback operation, the manipulation of data in the transaction does not continue into the database. In the event that no partial transaction can commit to the database it will leave the database in an inconsistent state.

Internally, multi-user databases store and process transactions, often by using transaction ID or XID.

There are several different ways for transactions to be executed other than the simple way documented above. Layered transactions, for example, are transactions containing statements in them that start new transactions (ie sub-transactions). Multi-level transactions are variants of multilevel transactions where sub-transactions occur on different levels of layered system architecture (for example, with one operation at the machine-database level, one operation in system-level operations). The other type of transaction is a compensation transaction.

In SQL

Transactions are available in most SQL database implementations, albeit with varying degrees of resilience. (MySQL, for example, began to support transactions from version 5.5, by switching to an InnoDB storage engine.) The storage engine that was previously used, MyISAM does not support transactions.)

Transactions usually begin by using the BEGIN command (although the SQL standard specifies START TRANSACTION ). When the system processes the COMMIT statement, the transaction ends with a successful completion. The ROLLBACK statement may also terminate the transaction, canceling any work done since BEGIN TRANSACTION . If autocommit is disabled using START TRANSACTION , autocommit will also be re-enabled at the end of the transaction.

One can set the level of isolation for individual transactional operations as well as globally. At the level of COMMITMENT READ, the result of any work performed after the transaction has started, but before it expires, will remain invisible to other database users until it is complete. At the lowest level (READ UNCOMMITTED), which is sometimes used to ensure high concurrency, the changes will be visible.

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Database object

The relational database usually consists of tables with fixed-size fields and thus records. The object database consists of a variable sized clump (probably incorporating mime or serial types). The basic similarity is the beginning and commitment or rollback.

After starting the transaction, the database or object record is locked, either read-only or read-write. Reading and writing may then occur. Once the users (and apps) are happy, the changes are made or rolled back atomically, so that at the end of the transaction there is no inconsistency.

Database Transactions, part 1: Introduction - YouTube

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Distributed transactions

The database system implements distributed transactions as transactions that access data through multiple nodes. Distributed transactions enforce ACID properties through multiple nodes, and may include systems such as databases, storage managers, file systems, messaging systems, and other data managers. In a distributed transaction, there is usually an entity that coordinates all processes to ensure that all parts of the transaction are applied to all relevant systems.

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Transactional file system

The Namesys Reiser4 filesystem for Linux supports transactions, and in Microsoft Windows Vista, the Microsoft NTFS file system supports distributed transactions across the network. There has been research into more coherent data system files, such as Warp Transactional Filesystem (WTF).