[转载]——Automatic Tuning of Undo_retention Causes Space Problems (文档 ID 420525.1)

Automatic Tuning of Undo_retention Causes Space Problems (文档 ID 420525.1)

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In this Document

Oracle Database - Enterprise Edition - Version 10.2.0.4 to 10.2.0.4 [Release 10.2]
Oracle Database - Enterprise Edition - Version 11.2.0.4 to 11.2.0.4 [Release 11.2]
Oracle Database Cloud Schema Service - Version N/A and later
Oracle Database Exadata Express Cloud Service - Version N/A and later
Oracle Database Exadata Cloud Machine - Version N/A and later
Information in this document applies to any platform.
Oracle Server Enterprise Edition - Version: 10.2.0.1 to 10.2.0.3 -- fixed by patchset 10.2.0.4 and no issues on this at 11g

*** Checked for currency: 01-Dec-2015 ***

You have verified that Document 413732.1 is not applicable and the problem is not a misunderstanding in the way EXPIRED/UNEXPIRED are used and reused over time.

Look for:

1. Whether the undo is automatically managed by the database by checking the following instance parameter:

UNDO_MANAGEMENT=AUTO

2. Whether the undo tablespace is fixed in size:

SQL> SELECT autoextensible
     FROM dba_data_files
     WHERE tablespace_name='<UNDO_TABLESPACE_NAME>'

This returns "NO" for all the undo tablespace datafiles.

3. The undo tablespace is already sized such that it always has more than enough space to store all the undo generated within the undo_retention time, and the in-use undo space never exceeds the undo tablespace warning alert threshold (see below for the query to show the thresholds).
4. The tablespace threshold alerts recommend that the DBA add more space to the undo tablespace:

SQL> SELECT creation_time, metric_value, message_type, reason, suggested_action
     FROM dba_outstanding_alerts
     WHERE object_name='<UNDO_TABLESPACE_NAME>';

This returns a suggested action of: "Add space to the tablespace".

Or,

This recommendation has been reported in the past but the condition has now cleared:

SQL> SELECT creation_time, metric_value, message_type, reason, suggested_action, resolution
     FROM dba_alert_history
     WHERE object_name='<UNDO_TABLESPACE_NAME>';

5. The undo tablespace in-use space exceeded the warning alert threshold at some point in time. To see the warning alert percentage threshold, issue:

SQL> SELECT object_type, object_name, warning_value, critical_value
FROM dba_thresholds
WHERE object_type='TABLESPACE';

To see the (current) undo tablespace percent of space in use:

SQL> SELECT
         ((SELECT (NVL(SUM(bytes),0))
           FROM dba_undo_extents
           WHERE tablespace_name='<UNDO_TABLESPACE_NAME>'
           AND status IN ('ACTIVE','UNEXPIRED')) * 100)/        
         (SELECT SUM(bytes)
          FROM dba_data_files
          WHERE tablespace_name='<UNDO_TABLESPACE_NAME>')
         "PCT_INUSE"
     FROM dual;

The cause of this problem has been identified in:
Bug:5387030 - AUTOMATIC TUNING OF UNDO_RETENTION CAUSING SPACE PROBLEMS

It is caused by a wrong calculation of the tuned undo retention value.

Bug:5387030 is fixed in RDBMS 11.1.

To implement a solution for Bug:5387030, please execute any of the below alternative solutions:

• Upgrade to 11.1 in which Bug:5387030 is fixed
  
  OR

• Apply patchset release 10.2.0.4 or higher in which Bug:5387030 is fixed.
  
  OR

• Download and apply interim Patch:5387030, if available for your platform and RDBMS release. To check for conflicting patches, please use the MOS Patch Planner Tool. If no patch is available, file a Service Request through My Oracle Support for your specific Oracle version and platform.
  
  OR

• Use any of the following workarounds:

1. Set the AUTOEXTEND and MAXSIZE attributes of each datafile of the undo tablespace in such a way that they are autoextensible and the MAXSIZE is equal to the current size (so the undo tablespace now has the AUTOEXTEND attribute but does not autoextend):

SQL> ALTER DATABASE DATAFILE '<datafile_flename>' AUTOEXTEND ON MAXSIZE <current_size>