Oracle Database is a powerful relational database management system (RDBMS) that allows organizations to store and manage large amounts of data efficiently. However, like any complex software, Oracle databases can encounter various errors that may disrupt normal operations. One such error is ora-00054: resource busy and acquire with nowait specified or timeout expired. This error typically occurs when a database resource (like a table or index) is locked by another session, and an attempt is made to acquire it with a NOWAIT clause or a timeout setting.
This article explores what ora-00054: resource busy and acquire with nowait specified or timeout expired is, its causes, and how to resolve it. Whether you are a database administrator, developer, or someone trying to troubleshoot the error, this guide will help you understand and handle it effectively.
What Is ora-00054: resource busy and acquire with nowait specified or timeout expired?
The ora-00054: resource busy and acquire with nowait specified or timeout expirederror is an Oracle Database error message indicating that a resource is currently locked by another session. When you attempt to acquire this resource (for example, during a DDL operation or when trying to access a table), Oracle detects that the resource is busy. The NOWAIT option or a specific timeout setting you applied means that the operation cannot wait for the lock to be released. As a result, Oracle raises the ora-00054: resource busy and acquire with nowait specified or timeout expired.
Here’s the general syntax of the error message:
The NOWAIT keyword in an SQL command tells Oracle not to wait if the resource is locked by another session. Similarly, if a timeout is specified and the resource is not available within that time frame, the error will be triggered.
Causes of ora-00054: resource busy and acquire with nowait specified or timeout expired
1. Locked Resources
The most common cause of ora-00054: resource busy and acquire with nowait specified or timeout expired. Oracle uses various types of locks (such as row-level locks, table-level locks, and system-level locks) to ensure data integrity and prevent conflicts. When one session holds a lock on a resource (e.g., a table) and another session tries to access it using NOWAIT, the database cannot wait for the lock to be released and raises the ora-00054: resource busy and acquire with nowait specified or timeout expired.
2. DDL Operations and Locking
Certain Data Definition Language (DDL) operations in Oracle require exclusive locks on database objects. For example, when you perform operations like ALTER TABLE, DROP TABLE, or CREATE INDEX, Oracle locks the table or index involved in the operation. If another session is accessing the same object, the second session may encounter the ora-00054: resource busy and acquire with nowait specified or timeout expired if it specifies NOWAIT or a timeout setting.
3. Long-Running Transactions
If there is a long-running transaction that holds a lock on a resource for an extended period, other sessions may experience delays in accessing that resource. This could be especially problematic in high-concurrency environments where multiple sessions are trying to access the same resources simultaneously.
4. Hotspot Resources
Certain high-demand resources (like popular tables or frequently queried indexes) may experience frequent locking, especially during peak usage times. When these resources are locked, attempts to access them by other sessions can lead to the ORA-00054 error if the timeout or NOWAIT is applied.
How ORA-00054 Affects Database Operations
The ORA-00054 error can have a significant impact on your database operations, especially in environments that require high availability and minimal downtime. When this error occurs, the following issues may arise:
- Transaction Failures: If you are performing critical operations, such as updates or inserts, your transaction could fail, leading to a rollback.
- Application Downtime: Applications relying on database access could experience delays or failures, affecting end-users.
- Performance Bottlenecks: Multiple sessions trying to acquire a locked resource can lead to performance degradation, affecting the overall efficiency of the database.
How to Resolve ORA-00054
Now that we understand the causes and effects of ORA-00054, let’s explore the ways to resolve this error. There are several strategies and best practices that can be applied to minimize or eliminate occurrences of ORA-00054.
1. Use the FOR UPDATE Clause with Proper Locking
If you are performing SELECT queries and intending to lock rows, using the FOR UPDATE clause is a good way to control the locking behavior. The FOR UPDATE clause locks the rows in a transaction, ensuring that no other sessions can modify the rows while your transaction is ongoing.
For example:
This will lock the rows returned by the query until the transaction is committed or rolled back.
2. Increase the Timeout Value
If you encounter ORA-00054 due to a timeout expiration, you may consider increasing the timeout value. This gives the database more time to wait before raising the error. You can specify the TIMEOUT parameter to define how long the session should wait for the lock to be released.
For example:
This command waits for 30 seconds before throwing an error if the rows are still locked.
3. Use the NOWAIT Option Cautiously
The NOWAIT option can be useful when you want to ensure that a session does not wait indefinitely for a resource. However, it should be used with caution. If you encounter frequent occurrences of the ORA-00054 error, you may want to reconsider using NOWAIT or adjust its usage based on your database environment.
If you must use NOWAIT, try to identify and eliminate unnecessary locking conflicts. Otherwise, remove NOWAIT to allow the session to wait for a lock to be released.
4. Identify and Kill Long-Running Sessions
One of the most effective ways to resolve resource contention and prevent ORA-00054 is by identifying long-running sessions that are holding locks for extended periods. You can query the Oracle system views to identify such sessions and then terminate or resolve them.
Use the following query to find blocking sessions:
After identifying the problematic session, you can either wait for it to complete or terminate it using:
This will release the lock and allow other sessions to proceed.
5. Avoid Excessive Locking with DDL Operations
Whenever possible, try to avoid performing DDL operations during peak usage times, as these operations can place locks on resources that prevent other users from accessing them. If you must perform a DDL operation, consider scheduling it during off-peak hours to minimize the chances of encountering the ora-00054: resource busy and acquire with nowait specified or timeout expired.
6. Monitor and Optimize Database Performance
Regularly monitor and optimize your Oracle Database’s performance to avoid resource contention. Ensure that your database schema is well-designed, with appropriate indexing and partitioning. This can help minimize lock conflicts and reduce the chances of encountering the ora-00054: resource busy and acquire with nowait specified or timeout expired.
7. Set Appropriate Isolation Levels
Transaction isolation levels define how transactions interact with each other. In environments where lock conflicts are frequent, consider adjusting the isolation level. For example, using READ COMMITTED isolation level might reduce the likelihood of encountering locked resources.
This will reduce the chances of encountering ora-00054: resource busy and acquire with nowait specified or timeout expired in some scenarios, but it should be used carefully as it could affect transaction consistency.
8. Resolve Locking Issues at the Application Level
If your application is generating frequent locking conflicts, consider revising your code to handle concurrency better. For example, you could use optimistic locking or implement a queuing mechanism that ensures that resources are accessed in an orderly fashion.
Conclusion
The ora-00054: resource busy and acquire with nowait specified or timeout expired specified or timeout expired” — can be a frustrating issue for Oracle Database users, but it is not insurmountable. By understanding the causes and following best practices such as using proper locking techniques, increasing timeouts, and optimizing database performance, you can significantly reduce or eliminate occurrences of this error.
By carefully managing locking mechanisms, monitoring long-running transactions, and applying the correct isolation levels, you can improve concurrency and keep your database running smoothly. With these strategies in mind, you will be better equipped to handle ora-00054: resource busy and acquire with nowait specified or timeout expired and ensure that your Oracle Database performs optimally in any scenario.
