Common scenarios and solutions for table locking in Oracle databases

Common scenarios and solutions for table locking in Oracle database

In Oracle database, table locking is a common database performance problem. When multiple sessions access it at the same time, When using the same table, it may cause the table to be locked, thus affecting the performance and stability of the system. This article will discuss some common table locking scenarios and provide corresponding solutions and code examples.

1. Scenario 1: Long-term transactions cause table locks

This scenario usually occurs when a long-term lock is occupied during the execution of a session. table, causing other sessions to be unable to operate on the table. To solve this problem, you can release the table lock by finding the long-running transaction and aborting it. The following is a sample code:

SELECT SID, SERIAL#, SQL_ID, STATUS
FROM V$SESSION
WHERE STATUS = 'ACTIVE' AND SQL_ID IS NOT NULL
ORDER BY LAST_CALL_ET DESC;

ALTER SYSTEM KILL SESSION 'SID,SERIAL#';

2. Scenario 2: Concurrent updates cause table locks

When multiple sessions try to update the same row of data at the same time , row-level locks may occur causing table locks. To avoid this situation, you can use row-level locks or add appropriate waiting times to your code. The following is a sample code:

SELECT *
FROM table_name
WHERE column_name = 'value'
FOR UPDATE;

3. Scenario 3: DDL operation causes table lock

When a session performs a DDL operation (such as ALTER TABLE , DROP TABLE, etc.), the entire table may be locked, preventing other sessions from operating on the table. To solve this problem, you can perform DDL operations during non-working hours and enable DDL locks when necessary. The following is a sample code:

LOCK TABLE table_name IN EXCLUSIVE MODE;

4. Scenario 4: Table lock caused by index

If a query does not use the index correctly, it may cause Table level locking. To avoid this situation, you can optimize the query statement to use the correct index. The following is a sample code:

CREATE INDEX index_name ON table_name(column_name);

Summary:

Table locking is a common performance problem in Oracle databases, but by understanding common locking scenarios and corresponding solutions, we can effectively avoid them Or resolve table locking issues. In practical applications, it is necessary to select the appropriate solution according to the specific situation, and adjust and optimize it according to the actual situation to ensure the stability and performance of the system.

(Note: The above code is for reference only, please adjust and test according to the actual situation.)

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