Database Hangs Because SMON Is Taking 100% CPU Doing Transaction Recovery (Doc ID 414242.1)

Last updated on JANUARY 31, 2017

Applies to:

Oracle Database - Enterprise Edition - Version 8.1.7.0 to 11.2.0.3 [Release 8.1.7 to 11.2]
Oracle Database - Enterprise Edition - Version 11.2.0.4 to 11.2.0.4 [Release 11.2]
Information in this document applies to any platform.

Goal

Checked for relevance on 24-Oct-2011

After killing a large running transaction, either by killing the process or aborting the database, the database may appear to hang and/or the SMON background process is taking all the available cpu. Basically SMON is in the progress of rolling back this terminated large transaction, which can be time consuming. As a result of this users often try to restart the database, but because a shutdown immediate will hang, the database is often aborted. Please note that stopping the database will actually make things worse and will not decrease the amount of work SMON needs to perfom to complete the rollback.

The message 'Waiting for smon to disable tx recovery' will be posted in the alert log as well.

You may also see alert log  messages:

SMON: about to recover undo segment 12
SMON: mark undo segment 12 as available
SMON: about to recover undo segment 12
*** 2009-11-12 10:08:11.389
SMON: mark undo segment 12 as available

Solution

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