How-To Resolve Enqueue Errors in Any Version of Oracle Database

 As an Oracle database administrator, you've likely encountered errors that make your heart skip a beat. One such error is ORA-00240: control file enqueue held for more than 120 seconds. But before you panic, let's break down what this error means and how to address it.

This error occurs when the control file enqueue is held for an extended period (over 120 seconds). The control file is a critical component of the Oracle database, managing database structure and integrity.

If you see this error occasionally, and your instance remains up and running, it's likely a fleeting glitch. Ignore it and move on.

However, if:

• The error occurs frequently
• Your instance hangs or crashes
• Performance is severely impacted

You need to be worried about it.

In my experience, ORA-00240 can be triggered by:

• High session counts conflicting with OS ulimits
• Shared pool latch contention (as noted in some MOS documents)
• Bugs in the Oracle software (resolvable with PSUs or one-off patches)

You should be checking:

• Check alert logs for frequency and patterns.
• Verify OS ulimits are adequately set.
• Monitor shared pool latch contention using

SELECT

  NAME,

  GETS,

  WAITS,

  IMP_GETS,

  IMP_WAITS

FROM

  V$LATCH

WHERE

  NAME = 'shared pool';

Don't panic over occasional ORA-00240 errors. However, frequent occurrences warrant immediate attention. By understanding the causes and taking proactive steps, you'll minimize downtime and ensure your Oracle database runs smoothly.