Oracle Deadlock: Check & Resolve Methods

1 year ago
Sophia Anderson
2 minutes

There are various methods available in Oracle database to query and handle deadlocks. Some common methods include:

  1. To check for deadlocks, you can use the following SQL query to see if there are any current deadlocks.
SELECT DISTINCT l1.sid || ',' || l1.serial# || ',' || l1.username blocker,
                l2.sid || ',' || l2.serial# || ',' || l2.username waiter,
                w.event,
                w.p1 || ',' || w.p2 || ',' || w.p3 AS resource
FROM v$lock l1, v$lock l2, v$session w
WHERE l1.block = 1
  AND l2.request > 0
  AND l1.id1 = l2.id1
  AND l1.id2 = l2.id2
  AND l2.sid = w.sid;

This query will return information related to deadlocks, including the session ID, username, waiting event, and resource of the blocking and blocked processes.

  1. To resolve a deadlock: Once a deadlock is identified, it can be resolved by using one of the following methods:
  2. Waiting for unlock: If deadlock is caused by resource contention, waiting for the release of resources may be necessary. This could involve modifying the application to prevent resource contention.
  3. Rollback of transactions: If a deadlock is caused by contention between transactions, one of the transactions can be rolled back to release resources and resolve the deadlock.
  4. Force session termination: If deadlock cannot be resolved through other means, you can use the following statement to terminate the blocked process: ALTER SYSTEM KILL SESSION ‘sid,serial#’;

    Where ‘sid’ and ‘serial#’ are the session ID and serial number of the blocked process.

  5. Optimizing queries and transactions: Deadlocks are often caused by poorly designed or improperly executed queries and transactions. By optimizing queries and transactions, the occurrence of deadlocks can be reduced. For example, ensuring transactions are committed promptly, avoiding operations that hold locks for extended periods within transactions, and correctly utilizing transaction isolation levels.

It is important to note that deadlock is a complex issue, and resolving deadlock may require analysis and adjustments based on the specific business environment and database design. Therefore, when dealing with deadlock issues, it is recommended to consult with a database administrator or a professional Oracle support team to obtain more accurate and targeted advice.

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