How to detect table locks in Oracle database

In Oracle database, table lock is a locking operation on the database table to ensure the integrity and consistency of the data. Table locks are divided into shared locks and exclusive locks. Shared locks allow multiple sessions to read data at the same time, but do not allow other sessions to modify the data; exclusive locks only allow one session to write operations, and other sessions cannot read or modify the data. . In practical applications, we often need to detect table lock situations to ensure the smooth progress of database operations.

In Oracle database, table locks can be detected through the following methods:

1. Use DBA_LOCKView: By querying DBA_LOCK View, you can view all lock information in the current database, including lock type, session ID holding the lock, etc. The following is a sample code:

SELECT * FROM DBA_LOCK WHERE LOCK_TYPE = 'TM' AND MODE_HELD IS NOT NULL;

This query statement can list all current table lock information, where LOCK_TYPE = 'TM' represents a table lock, MODE_HELD IS NOT NULL indicates that the current session holds the lock.

2. Use V$LOCK view: V$LOCKThe view contains all lock information in the current database. You can view the specific lock information by querying this view. , including the type of lock, the session ID holding the lock, etc. The following is a sample code:

SELECT * FROM V$LOCK WHERE TYPE = 'TM';

This query statement can list all current table lock information, where TYPE = 'TM' indicates table locks.

3. Use DBA_BLOCKERS and DBA_WAITERS views: By querying these two views, you can view all session information that is blocked and waiting for locks in the current database. The following is sample code:

SELECT /*+gather_plan_statistics*/
 SHOLDING_SESSION SEQ POS TSYM LMODE REQUEST PCB
FROM 
 DBA_LOCK_INTERNAL A,
 DBA_LOCK_INTERNAL B,
 V$SESSION S1, 
 V$SESSION S2
WHERE 
 A.SID1 = S1.SID AND
 B.SID1 = S2.SID AND
 S1.USERNAME IS NOT NULL AND
 S2.USERNAME IS NOT NULL AND
 A.SID1 = B.SID1 AND
 A.SID2 = B.SID2;

By analyzing the DBA_BLOCKERS and DBA_WAITERS views, you can understand which sessions are blocked by locks and which sessions are waiting for locks.

Through the above methods, table locks can be detected in the Oracle database, potential lock conflicts can be discovered and resolved in a timely manner, and normal database operations can be ensured.

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