How does oracle lock the table

Oracle database is an open standard relational database system, which has the ability to manage data in enterprise applications. In Oracle database, table is the key object of data storage, and table locking is one of the problems that database administrators must face. This paper will introduce the knowledge about table locking in Oracle database, including the types of table locking, the usage scenarios of locking, and how to lock tables.

I. Table Lock Types There are two types of table locks in Oracle database: exclusive locks and shared locks.

Exclusive lock: Also known as mutex lock, it is an exclusive lock. Once a transaction locks a table, other transactions cannot do anything on the table until the locked transaction ends. Exclusive locks are used to modify the table structure, add, delete and update data.

Shared lock: Also known as shared lock, multiple transactions can hold the lock at the same time because they will not affect each other. Shared locks are used for read-only operations.

Second, the use scenarios of locking In practical applications, table locking includes the following common use scenarios:

Concurrent transactions lock tables: When multiple transactions access the same table, concurrency problems may occur. Transaction A is accessing the record on the table, and transaction B needs to access the same record. If concurrency is not handled, two transactions will access the table at the same time, resulting in data conflict. The solution is to use exclusive locks to lock tables and records and prevent other transactions from accessing them. Database backup locking table: When database backup is performed, the table must be locked to prevent data from being modified during backup. After the backup is completed, you can release the table lock. Maintain table structure and lock the table: when modifying, adding or deleting the table structure, it is necessary to lock the table to prevent other operations from interfering with the table structure. Third, how to lock the table Oracle database provides a variety of ways to lock the table. We can use the ALTER TABLE statement to add or delete the command to lock the table, or we can add a FOR UPDATE or FOR SHARE clause in the query to specify the lock type.

Here are some SQL examples to illustrate how to use Oracle to lock tables:

Use ALTER TABLE statement: LOCK TABLE table name IN SHARE MODE; -shared lock mode LOCK TABLE table name IN EXCLUSIVE MODE; -exclusive locks model

Use the FOR UPDATE or FOR SHARE clause in the SELECT statement: SELECT column name FROM table name WHERE condition FOR UPDATE; -exclusive lock SELECT column name FROM table name WHERE condition FOR SHARE; -shared lock

In the process of using the lock table, you need to pay attention to the following points:

Locking the table will reduce the performance of the database. Therefore, when using table locks, we should minimize the use time and release the locks when they are not needed. If you know the release time of table locks, you can use shared locks to improve system concurrency while waiting for exclusive locks. When locking tables, you should pay attention to the consistency of transactions. If multiple transactions try to modify the same record at the same time, only one transaction can succeed, and the other transactions will fail. To sum up, table locking in Oracle database not only ensures data security, but also needs to pay attention to database performance and transaction consistency. For large enterprise applications, any decision to lock a table needs careful consideration and evaluation. Of course, after mastering the basic knowledge of table locking, we can better use Oracle database to complete function development and operation and maintenance.