How to solve deadlock in Oracle? How to avoid it?

In the process of using Oracle database recently, you may have encountered a deadlock situation. These deadlocks can cause connections to fail, queries to fail to complete, and even the entire database system to crash. Therefore, resolving deadlock problems is a very important task for Oracle database administrators.

In this article, we will introduce the basic concepts, causes and solutions of Oracle deadlocks. We'll also cover some best practices to avoid deadlocks.

What is deadlock?

Deadlock is a situation that occurs when multiple processes try to monopolize resources held by other processes. In Oracle, it is usually caused by waiting for each other to lock rows. If process A locks row If row Y is now locked by another process C, and C attempts to monopolize row X owned by process A, then all three processes will be blocked, resulting in a deadlock.

In Oracle, deadlocks usually cause processes waiting for resources to be unable to continue, and in some cases, may cause the entire database system to crash.

Causes of Deadlock

Deadlock is often caused by multiple processes trying to access the same database object at the same time. Two or more processes are required for a deadlock to occur. For example, when two or more processes write to the same table at the same time, the processes wait for each other's locks. They cannot proceed due to the circular dependency between them.

The following are several possible causes of deadlock:

1. Use different resources to operate at the same time

For example, one department may try to update a When another department is trying to sell this product, the two processes will wait for each other to release the lock.

2. The lock duration is too long

If a process occupies the lock for a long time and other processes need to access the lock, a deadlock may occur.

3. Excessive number of processes

In some cases, there may be a large number of processes accessing the same resource. The dependencies between these processes can be complex, leading to deadlocks.

How to solve deadlock?

If you often encounter deadlock problems, then you should take some actions to solve the problem. The following are some methods that can be used to solve deadlocks:

1. Optimizing the database system

Optimizing the database system can reduce the occurrence of deadlocks, for example, dividing the number of users who need to access the same resource into Processes are merged into a single process group.

2. Adhere to best practices

Adopting best practices can reduce the occurrence of deadlocks. For example, taking only the shortest possible time when writing to the database, distributing the workload appropriately, etc.

3. Avoid excessive occupation of resources

When a process occupies a resource, it should clearly specify the length of time it will occupy, and ensure that it is released immediately after the occupation time is over. this resource.

4. Use the deadlock detection function provided by Oracle

Oracle provides some deadlock detection functions based on SQL queries and performance monitoring tools. These tools can quickly locate and resolve deadlock problems, helping you manage your database system more efficiently.

Summary

In the process of using the Oracle database system, it is very common to encounter deadlock problems. These deadlock issues can severely impact database performance and reliability. You should take the steps listed above to resolve these issues to ensure that your Oracle database operates efficiently.

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