What is the phenomenon of mysql deadlock?

Mysql deadlock phenomenon: 1. The database connection thread will become unresponsive during a deadlock; 2. Deadlock events are reported in the database log; 3. The deadlock detection mechanism is triggered; 4. Database performance decreases .

The operating system of this tutorial: Windows 10 system, mysql version 8.0, Dell G3 computer.

MySQL is a widely used relational database management system that is efficient, stable and reliable. However, due to the need for concurrent access to the database, MySQL may experience deadlocks, which can negatively impact the performance and overall operation of the database. This article will explore the MySQL deadlock phenomenon and its characteristics.

Deadlock refers to a situation where two or more concurrent transactions hold the resources required by each other and wait for the other party to release the resources. When this happens, these transactions cannot continue to execute, forming a deadlock.

In MySQL, deadlock usually occurs under the following circumstances:

1. Concurrent transactions perform reverse locking order: When two transactions obtain different After obtaining the resource, a deadlock will occur when trying to obtain the resource already held by the other party.

2. Concurrent transactions request the same resource at the same time: When multiple transactions request the same resource at the same time, only one transaction can successfully obtain the resource, and other transactions will be blocked, which may lead to death. lock occurs.

The deadlock phenomenon has some characteristics in MySQL:

1. When deadlock occurs, the database connection thread will become unresponsive: If a deadlock occurs, the database connection thread will It will be in a waiting state and no more requests will be sent to the database.

2. The deadlock event is reported in the database log: The MySQL log will record the specific information of the deadlock event, including the transaction ID participating in the deadlock, the deadlock chain, and the blocked thread, etc. .

3. The deadlock detection mechanism is triggered: MySQL has a deadlock detection mechanism that can automatically detect and relieve deadlocks. When the deadlock detection mechanism is triggered, the database will automatically select a transaction to roll back to relieve the deadlock.

4. Database performance degradation: Deadlock will cause database performance degradation, because deadlock will block the execution of concurrent transactions, causing other transactions to wait longer to complete.

How to deal with MySQL deadlock?

1. Deadlock avoidance: Avoid conflicts caused by concurrent transactions by reasonably designing the order of transactions and locks. Database locking mechanisms, transaction isolation levels, and reasonable index design can be used to reduce the occurrence of deadlocks.

2. Deadlock detection and release: MySQL has a deadlock detection mechanism, but this does not guarantee that the deadlock can be released. Therefore, you can use database logging and monitoring tools to detect deadlocks in time and take appropriate measures.

3. Optimize database performance: Optimizing database performance can reduce the occurrence of deadlocks. By optimizing query statements, increasing the hardware resources of the database server, and adjusting database configuration parameters, the concurrent processing capabilities of the database can be improved.

In short, MySQL deadlock is a common problem when accessing the database concurrently. Understanding the deadlock phenomenon and its characteristics is critical to troubleshooting and solving deadlock problems. Through reasonable design, monitoring and tuning, the probability of deadlock can be reduced and the performance and stability of the database can be improved.

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