What are the reasons and solutions for table locks in Oracle?

Title: Reasons and solutions for table locking in Oracle

In Oracle database, table locking is one of the common problems in database operations. Table locks can cause database performance to degrade and applications to not function properly. This article will introduce the reasons why tables are locked in Oracle and provide specific code examples to solve this problem.

Cause

The reasons why the table is locked usually include the following points:

1. Transaction is not committed: When a transaction is operating on the table, other transactions are also If you hope to modify the same table, the table will be locked.
2. Concurrent access: Multiple users modify the same table at the same time, which may cause the table to be locked.
3. Database deadlock: When two transactions wait for each other to release resources, a deadlock will occur, and the table may also be locked by one of the transactions.

Solution

For different reasons, we can adopt different solutions to solve the problem of table being locked. The following are some common solutions and specific code examples:

1. The transaction is not submitted

If the table is locked because the transaction is not submitted, it can be solved by the following methods:

-- 查找当前正在运行的事务
SELECT username, sid, serial# 
FROM v$session
WHERE blocking_session IS NOT NULL;

-- 查找正在运行的 SQL 语句
SELECT SQL_TEXT
FROM v$sql
WHERE sql_id = (SELECT sql_id FROM v$session WHERE sid = :sid);

Find the cause of the lock by querying the running transactions and SQL statements, and submit or roll back the transaction in a timely manner.

2. Concurrent access

If the table is locked due to multiple users modifying the table at the same time, the problem can be solved by adjusting the transaction isolation level or optimizing the SQL statement.

-- 调整事务隔离级别为READ COMMITTED
SET TRANSACTION ISOLATION LEVEL READ COMMITTED;

By adjusting the transaction isolation level to READ COMMITTED, you can reduce the possibility of the table being locked.

3. Database deadlock

If a database deadlock occurs and the table is locked, you can solve it through the following methods:

-- 查看死锁信息
SELECT a.sid, a.serial#, b.sid, b.serial#
FROM v$session a, v$session b
WHERE a.blocking_session = b.sid;

-- 终止导致死锁的会话
ALTER SYSTEM KILL SESSION 'sid,serial#';

Find out the cause of the deadlock by viewing the deadlock information session and terminate the session to release the table lock.

Conclusion

Table locking is a common problem in databases, but through reasonable investigation and solution, the impact of table locking can be effectively avoided or solved. In daily database operations, it is recommended to understand table locks and choose appropriate solutions according to the actual situation to improve database performance and stability.

Through this article’s introduction to the reasons and solutions for table locks in Oracle, I believe that readers will have a more comprehensive understanding of this problem and be able to better solve related database locking problems in actual work. .

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