MySql concurrency control: how to avoid resource conflicts

With the rapid development of Internet technology, concurrent access to database systems has become more and more common. The question that follows is how to control concurrent access efficiently and reliably to avoid data conflicts and resource competition. MySql, as a widely used relational database system, its concurrency control mechanism has become an important research topic. This article will discuss MySql's concurrency control technology, including transactions, locks, and MVCC, and explore how to ensure the security and stability of the database in a multi-user, high-concurrency environment.

Transaction
Transaction is one of the most basic concurrency control technologies in the database. A transaction is composed of a series of database operation statements, which are either all executed or not executed at all. Transactions can ensure the consistency and integrity of the database and avoid data conflicts when multiple users modify data at the same time. In MySql, transactions are implemented using the four characteristics of ACID (atomicity, consistency, isolation, and durability). Atomicity means that the entire transaction must be regarded as a single operation, and either all executions are successful or all executions fail; consistency means that the state of the database must be consistent before and after the transaction is executed; isolation means that the execution of the transaction cannot be interrupted by other transactions Interference; and durability means that after the transaction is executed, its modified data should be permanently saved in the database.

Lock
Lock is one of the common means to control concurrent access. Its function is to lock and protect shared resources before accessing them to prevent other users from modifying the resources during this period. In MySql, commonly used locks include table-level locks and row-level locks. Table-level locks lock and protect the entire table, while row-level locks only lock certain rows in the table. Row-level locks are more fine-grained than table-level locks and can avoid resource waste and concurrency issues, but they also make management and maintenance more difficult.

MVCC
MVCC (Multi-version Concurrency Control) is a concurrency control technology. Its basic idea is to record different time versions of data and provide different data views between different users. When each transaction is executed, you will see the database state at a specific moment, and this state includes the data version generated by the committed transaction. MySql's MVCC implementation is mainly based on the InnoDB storage engine. Its basic principle is to retain a unique transaction ID for each transaction. During the transaction running, InnoDB will create row versions and save historical versions of data, as well as version numbers and Transaction ID and other related information. In MVCC, each transaction can read committed data or its own modified data, but cannot read uncommitted data of other transactions.

Summary
MySql’s concurrency control mechanism consists of three aspects: transactions, locks and MVCC. Through the application of these technologies, resource conflicts and data consistency problems can be effectively avoided, thereby ensuring the database security and stability. In actual development, we should choose appropriate technical means based on business needs and specific circumstances, and apply these technologies flexibly to meet the needs of high concurrent access and ensure system performance and reliability.

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