What is the default transaction isolation level of mysql?

MySQL is a widely used relational database management system that supports transaction processing. A transaction is a set of database operations that are executed together as a logical unit. In order to ensure transaction consistency and isolation, MySQL provides different transaction isolation levels.

The operating environment of this tutorial: windows10 system, mysql8.0.16 version, DELL G3 computer.

MySQL is a widely used relational database management system that supports transaction processing. A transaction is a set of database operations that are executed together as a logical unit. In order to ensure transaction consistency and isolation, MySQL provides different transaction isolation levels.

Transaction isolation level defines the visibility and scope of influence between operations within a transaction and other transactions. MySQL provides four transaction isolation levels: READ UNCOMMITTED (read uncommitted), READ COMMITTED (read committed), REPEATABLE READ (repeatable reading) and SERIALIZABLE (serializable). These isolation levels in turn provide a higher degree of isolation, but may also result in higher concurrency performance overhead.

By default, MySQL’s transaction isolation level is REPEATABLE READ. At this level, a transaction creates a consistent view, a snapshot of the database at a point in time when the transaction began. This means that the data that a transaction sees during execution is different from the data that other transactions modify concurrently. Even if other transactions modify some data, what the transaction sees in its own consistency view is still the snapshot at the beginning of the transaction.

Under the REPEATABLE READ level, the transaction can guarantee the following points:

1. The data read is consistent with the beginning of the transaction and will not change during the execution of the transaction.

2. Changes made by other parallel transactions during the transaction are invisible to the transaction and will not affect the data read by the transaction.

3. Changes made by a transaction to other transactions are invisible, and other parallel transactions cannot read uncommitted data in the transaction.

REPEATABLE The advantage of the READ level is that it provides high data consistency and isolation, and is suitable for scenarios where multiple concurrent transactions read the same data. However, it can also result in higher concurrency performance overhead and lock contention.

In actual applications, we can choose the appropriate transaction isolation level based on specific business needs and performance requirements. If you need higher concurrency performance and lower lock contention, you can consider lowering the transaction isolation level. If you pay more attention to data consistency and isolation, you can choose a higher transaction isolation level.

MySQL provides statements to set the transaction isolation level, which can be used before the transaction starts or within the transaction. For example, you can use the following statement to set the transaction isolation level to READ COMMITTED:

SET TRANSACTION ISOLATION LEVEL READ COMMITTED;

In short, the default transaction isolation level of MySQL is REPEATABLE READ, which provides higher data consistency and isolation, but may bring higher concurrency performance overhead. According to the specific application scenario, we can flexibly choose the appropriate transaction isolation level.

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