In a database management system, a transaction is a logical unit of a series of database operations that either executes all successfully or all are rolled back. As one of the most commonly used relational database management systems, MySQL provides powerful transaction support to ensure data consistency and integrity.
The concept and characteristics of transactions
Transaction definition: A transaction is a logical unit of a set of database operations (such as query, insert, update, delete, etc.), which has four basic characteristics: atomicity, consistency, isolation, and durability (ACID).
Atomicity: All operations in a transaction are either executed successfully or rolled back, and there is no partial execution.
Consistency: The state of the database must be consistent before and after the transaction is executed, and the integrity constraints of the database must not be broken at the beginning and end of the transaction.
Isolation: Concurrently executed transactions are isolated from each other, and each transaction can only see the results that other transactions have committed, and will not be affected by the results that other transactions have not committed.
Durability: Once a transaction is committed, its modifications to the database are persisted and will not be lost even if the system fails.
Running status of a transaction: A transaction in MySQL has multiple running states, including active, partially committed, partially rollback, and committed.
MySQL provides a variety of ways to manage transactions, including implicit and explicit transactions. Here's how a MySQL transaction works:
Start a transaction: Use the begin, start transaction, or set autocommit=0 statements to start a new transaction. By default, MySQL runs in auto-commit mode, i.e., each statement is executed as a transaction and automatically committed.
Perform transactional operations: Perform a series of database operations in a transaction, such as querying, inserting, updating, deleting, and so on. These operations can be performed using SQL statements (such as insert, update, and delete) or stored procedures and functions.
Commit a transaction: Use a commit statement to commit a transaction, which permanently saves all operations in the transaction to the database. Once committed, the transaction enters the committed state, and the modified data becomes visible to other transactions.
Rollback Transaction: Use the rollback statement to roll back a transaction, undo all operations in the transaction, and restore the state before the transaction started. After a rollback, the transaction enters the Rolled Back state, and the modified data will not be visible to other transactions.
Set a savepoint: You can use the s**epoint statement to set a savepoint in a transaction, marking a subset of operations in the transaction as a single logical unit. If you need to roll back to a savepoint, you can use the rollback to s**epoint statement.
Set transaction isolation level: MySQL supports multiple transaction isolation levels, and you can use the set transaction isolation level statement to set the isolation level of transactions, such as read uncommitted, read committed, repeatable read, and serializable.
End Transaction: Use the end or commit statement to end the transaction. In auto-commit mode, when a transaction is committed or rolled back, MySQL automatically starts a new transaction.
Considerations for transactions
Transaction granularity: Try to keep the granularity of transactions to a minimum to reduce the time spent locking resources and improve concurrency performance.
Locking mechanism: In the environment of concurrent execution, transactions may cause lock conflicts. Optimize the locking mechanism by choosing the locking level wisely, avoiding holding the locks for a long time, and using indexes.
Exception handling: In a transaction, you should catch and handle possible exceptions to avoid the failure to roll back the transaction due to unhandled exceptions.
Performance optimization: Designing the database structure, using indexes, avoiding long transactions, and setting transaction isolation levels can improve the performance and efficiency of transaction processing.
MySQL database provides powerful transaction support to ensure the security and integrity of data operations through the atomicity, consistency, isolation, and durability of transactions. Enable transactions, perform transaction operations, commit or roll back transactions, set save points, and set transaction isolation levels to make MySQL transaction management more flexible and controllable. At the same time, it is necessary to pay attention to key points such as transaction granularity, locking mechanism, exception handling, and performance optimization to ensure the efficient operation of transactions and data consistency.