How to lock table in oracle

In Oracle database, when multiple users access the same table at the same time, data confusion may occur. At this time, we may need to lock the table to avoid this situation. There are multiple lock mechanisms in Oracle, including shared locks and exclusive locks. This article will introduce how to lock tables in Oracle.

1. Shared lock

Shared lock is the most common locking method. It allows multiple users to read the same data block or record at the same time, but does not allow the data block or record to be read at the same time. to modify.

The basic syntax of shared lock is as follows:

LOCK TABLE table_name IN SHARE MODE;

Among them, table_name is the name of the table that needs to be locked.

Shared locks will not block other users' shared locks, but will block exclusive locks. When a user holds a shared lock, other users can only acquire shared locks and cannot acquire exclusive locks.

2. Exclusive lock

Exclusive lock is another common locking method, which allows users to modify data rows and prevents other users from modifying the same data row at the same time.

The basic syntax of exclusive lock is as follows:

LOCK TABLE table_name IN EXCLUSIVE MODE

Similar to shared lock, table_name is the name of the table that needs to be locked.

Exclusive locks will block other users' exclusive locks and shared locks. When a user holds an exclusive lock, other users cannot obtain shared locks or exclusive locks.

3. How to use table locks

In Oracle, we can use the LOCK TABLE command to perform table locks. It should be noted that locking a table may prevent other users from performing operations, so you need to consider carefully before using table locks.

If you need to use table locks, it is best to perform it during off-peak periods to reduce the impact on other users.

When locking tables, you also need to follow the following principles:

1. Keep the locking time as short as possible and only lock when necessary.

2. Avoid deadlock. Deadlock refers to a state in which two or more processes wait for each other due to competition for resources. In order to avoid the occurrence of deadlock, it is necessary to determine the order of acquiring locks before locking the table, and acquire smaller locks first and then larger locks in the transaction.

3. When locking a table, you should lock the entire table instead of locking certain rows or columns in the table, which can minimize the locking time.

4. Before using a locked table, you should ensure that you have sufficient permissions. If not, you need to contact the database administrator.

Summary:

In Oracle database, table locking is an effective way to protect data integrity. However, table locking can also affect other users, so it needs to be used with caution. When using table locking, you should follow principles to minimize the impact on other users and prevent deadlocks from occurring.

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