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Description

The ORA-30006 error in Oracle Database indicates that a requested resource is currently unavailable or the Distributed Transaction Processing (DTP) service is undergoing relocation. This often occurs during high transaction volume or when DTP operations are in progress.

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Error Message

ORA-30006: resource busy; acquire with WAIT timeout expired or DTP service is unavailable

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Known Causes

4 known causes

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Resource Contention

Multiple sessions are attempting to access the same resource simultaneously, leading to a lock and timeout.

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DTP Service Relocation

The Distributed Transaction Processing (DTP) service is being moved or restarted, temporarily preventing access.

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Long-Running Transactions

A transaction is holding a lock on the resource for an extended period, blocking other sessions.

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Network Issues

Temporary network disruptions can interfere with DTP service availability.

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Solutions

4 solutions available

1. Identify and Terminate Blocking Sessions medium

Find the session holding the resource and terminate it if appropriate.

1

Connect to the Oracle database as a user with sufficient privileges (e.g., SYS, SYSTEM, or a DBA role).

2

Query the `V$SESSION` and `V$LOCK` views to identify the session that is holding the resource and the session(s) waiting for it.

SELECT 
    s1.sid, 
    s1.serial#, 
    s1.username, 
    s1.program, 
    s1.status, 
    s1.event, 
    l.sid, 
    l.type, 
    l.id1, 
    l.id2, 
    l.lmode, 
    l.request, 
    l.block 
FROM 
    v$session s1, v$lock l 
WHERE 
    s1.sid = l.sid 
    AND l.request > 0 
    AND l.block = 1 
ORDER BY 
    l.request DESC;

3

Analyze the output. The session with `BLOCK = 1` is the one holding the resource. The session with `REQUEST > 0` is the one waiting. Pay attention to the `EVENT` column for the waiting session to understand what it's waiting for.

4

If the blocking session is identified and it's not critical for its current operation, you can terminate it. Use the `ALTER SYSTEM KILL SESSION` command.

ALTER SYSTEM KILL SESSION 'sid,serial#'; -- Replace sid and serial# with the values from the blocking session

5

Verify that the ORA-30006 error is no longer occurring for the waiting session.

2. Increase WAIT Timeout for Lock Acquisition advanced

Adjust the `enqueue_resources` parameter to allow more time for lock acquisition.

1

Connect to the Oracle database as a user with `SYSDBA` privileges.

2

Check the current value of the `enqueue_resources` parameter.

SHOW PARAMETER enqueue_resources;

3

If the current value is low, consider increasing it. The default is typically 10. A common recommendation for busy systems is to set it higher, e.g., 100 or 200. This parameter controls the number of enqueue resources that can be active. Increasing it can help prevent ORA-30006 errors if the system is genuinely experiencing high contention and locks are being acquired and released rapidly.

ALTER SYSTEM SET enqueue_resources = 200 SCOPE=BOTH; -- Adjust the value as needed

4

Monitor the system after the change to see if the ORA-30006 errors are reduced. Note that this is a system-wide parameter and should be increased cautiously.

3. Optimize Application Logic for Lock Contention advanced

Review and refactor application code to reduce the duration and frequency of lock requests.

1

Analyze the application code that is frequently encountering the ORA-30006 error. Identify the specific SQL statements or PL/SQL blocks that are performing operations that lead to lock contention.

2

Examine the transactions. Are they holding locks for longer than necessary? Can they be broken down into smaller, more manageable transactions?

3

Consider using appropriate isolation levels for transactions. If a lower isolation level can be used without compromising data integrity, it might reduce lock contention. However, this requires careful analysis of business requirements.

4

Optimize SQL queries. Poorly performing queries can hold locks for extended periods. Ensure that indexes are used effectively and that queries are as efficient as possible.

5

Implement optimistic locking mechanisms if feasible. This involves checking if a record has been modified before attempting an update, rather than acquiring a pessimistic lock upfront.

6

Test changes thoroughly in a development or test environment before deploying to production.

4. Investigate and Resolve DTP Service Issues advanced

Diagnose and fix problems with the Distributed Transaction Processing (DTP) service if it's implicated.

1

The 'DTP service is unavailable' part of the error message suggests a potential issue with distributed transactions or the infrastructure supporting them (e.g., Oracle Net Services, XA protocols).

2

Check the Oracle Net Services configuration (`listener.ora`, `tnsnames.ora`) for any misconfigurations that might prevent proper communication between database instances involved in distributed transactions.

3

Examine the alert logs of all involved database instances for any errors related to distributed transactions or XA.

4

Verify the health and status of any transaction managers or middleware components that participate in distributed transactions.

5

If the issue is intermittent, try to correlate it with network stability or specific application activities that trigger distributed transactions.

6

Consult Oracle documentation or support for specific troubleshooting steps related to distributed transaction processing and XA issues.

Oracle Error ORA-30006: Resource Busy