Resolving ORA-00054: Resource Busy and Acquire with NOWAIT Specified

Introduction
Understanding the Cause
Step-by-Step Solutions
Example Scenario
Conclusion

Introduction

The ORA-00054: Resource Busy and Acquire with NOWAIT Specified error in Oracle Database occurs when a resource, such as a table or a row, is busy and a NOWAIT request is made to acquire it. This error can be disruptive, especially in environments that require high availability and performance. In this blog post, we'll explore the reasons behind this error and provide detailed steps to resolve it effectively.

Understanding the Cause

The ORA-00054 error happens when a session tries to access a resource that is already locked by another session, with the NOWAIT option specified. This means the request is set to fail immediately if the resource is not available, instead of waiting for the resource to be released. Common scenarios include:

- Attempting to lock a table or row for an update while another session is performing an operation on the same resource.
- Executing DDL statements like ALTER TABLE or DROP TABLE when the resource is in use.

Step-by-Step Solutions

### 1. Identify the Locking Session First, identify which session is holding the lock on the resource. You can use the following query to find this information: 

SELECT
    s.sid,
    s.serial#,
    s.username,
    s.osuser,
    l.type,
    l.id1,
    l.id2
FROM
    v$session s,
    v$lock l
WHERE
    s.sid = l.sid
AND
    l.block = 1;
### 2. Resolve the Lock Once you have identified the locking session, you can either wait for it to complete its operation or manually intervene by killing the session. To kill a session, use the following command: 

ALTER SYSTEM KILL SESSION 'SID,SERIAL#';
Replace SID and SERIAL# with the values obtained from the previous query.

### 3. Retry the Operation After resolving the lock, retry the operation that caused the ORA-00054 error. Ensure that you do not specify the NOWAIT option if you can afford to wait for the resource to be released.

Example Scenario

Let's go through an example scenario to illustrate these steps.

#### Step 1: Identify the Locking Session Suppose you encounter the ORA-00054 error while trying to execute an ALTER TABLE statement. Run the following query to identify the locking session: 

SELECT
    s.sid,
    s.serial#,
    s.username,
    s.osuser,
    l.type,
    l.id1,
    l.id2
FROM
    v$session s,
    v$lock l
WHERE
    s.sid = l.sid
AND
    l.block = 1;
Assume the query returns the following result: 
SID   SERIAL#   USERNAME   OSUSER
----  -------   --------   ------
123   45678     DBDOCS     oracle
#### Step 2: Kill the Locking Session Execute the following command to kill the session: 

ALTER SYSTEM KILL SESSION '123,45678';
#### Step 3: Retry the Operation After the session is killed, retry your ALTER TABLE statement: 

ALTER TABLE employees ADD (email VARCHAR2(100));
This time, the operation should complete successfully without encountering the ORA-00054 error.

Conclusion

The ORA-00054 error can interrupt database operations, but with the right approach, it can be resolved efficiently. By identifying and managing the locking sessions, you can ensure that your operations proceed smoothly. Regular monitoring and understanding of your database's locking behavior can also help in preventing such issues from occurring frequently.

By following these steps, you can effectively troubleshoot and resolve the ORA-00054 error, maintaining the high availability and performance of your Oracle Database.

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Last updated in July, 2024

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