mysql事务的英文简介：

The Indispensable Role of MySQL Transactions: A Comprehensive Guide In the realm of relational database management systems(RDBMS), MySQL stands out as one of the most widely used and versatile platforms. Its popularity stems from a combination of factors, including its open-source nature, robust feature set, and extensive community support. One of the cornerstone features of MySQL, and indeed any modern RDBMS, is the concept of transactions. Understanding MySQL transactions—often referred to in technical circles as MySQL Transactions or simply transactions within the MySQL context—is crucial for developing robust, reliable, and scalable database applications. This article delves into the intricacies of MySQL transactions, emphasizing their importance, mechanisms, benefits, and practical applications. What Are MySQL Transactions? At its core, a transaction in MySQL(and other RDBMS) represents a logical unit of work that is treated as a single, indivisible operation by the database system. This means that either all the operations within a transaction are successfully completed and committed to the database, or in the event of a failure, none of them are applied, and the database remains in a consistent state. Transactions encapsulate the ACID properties, which stand for: 1.Atomicity: Ensures that all operations within a transaction are treated as a single unit. If any part of the transaction fails, the entire transaction is rolled back to its initial state. 2.Consistency: Guarantees that a transaction will only bring the database from one valid state to another valid state. It enforces business rules and constraints. 3.Isolation: Ensures that the operations of concurrent transactions are isolated from one another. This prevents interference and maintains data integrity until transactions are committed. 4.Durability: Assures that once a transaction has been committed, its effects will persist even if the system crashes. Mechanisms Behind MySQL Transactions MySQL supports transactions through its storage engines, with the most notable being InnoDB and NDB(also known as NDBCLUSTER). InnoDB is the default storage engine in MySQL 5.5 and later versions, and it is designed to fully support ACID-compliant transactions. Heres a closer look at how MySQL transactions work under the hood: - Start Transaction: This is typically signaled bythe `START TRANSACTION,BEGIN`,or `BEGIN WORK` statements. It marks the beginning of a new transaction block. - Statement Execution: Within the transaction, SQL statements suchas `INSERT`,`UPDATE`, and`DELETE` are executed. These operations are queued until the transaction is committed or rolled back. - Savepoint Management: MySQL allows setting savepoints within a transaction using the`SAVEPOINT` statement. This can be useful for partially rolling back a transaction to a specific savepoint rather than abandoning all changes. - Commit: The COMMIT statement finalizes the transaction, making all changes permanent in the database. - Rollback: If something goes wrong, the`ROLLBACK` statement can be used to undo all operations performed since the start of the transaction or since the last savepoint. Isolation Levels in MySQL Transactions One of the key aspects of transaction management is isolation, which prevents concurrent transactions from interfering with each other. MySQL supports four isolation levels, defined by the SQL standard: 1.Read Uncommitted (READ-UNCOMMITTED): Allows a transaction to read changes made by other transactions even before they are committed. This can lead to dirty reads. 2.Read Committed (READ-COMMITTED): Ensures that a transaction can only read data that has been committed by other transactions. This prevents dirty reads but allows non-repeatable reads and phantom reads. 3.Repeatable Read (REPEATABLE-READ): Guarantees that within a transaction, queries will return the same data, preventing non-repeatable reads. However, phantomreads (where new rows