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How to fix ORA01555

Posted on 2010-01-09
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Oralce ORA01555 error in oracle 10g  How to fix it.
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Question by:yendluri
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by:yendluri
ID: 26273323
ORA 01555  Error in Oracle.
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Author Comment

by:yendluri
ID: 26273328
Oracle ORA 01555 Error
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Shaju Kumbalath earned 1000 total points
ID: 26273405
The UNDO tablespace is too small. Increase the size of the UNDO tablespace.
The UNDO tablespace should be large enough to store the undo data generated by
active transactions as well as those preserved to honor the undo retention setting.
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by:it-rex
it-rex earned 1000 total points
ID: 26276221
ORA01555 is the infamous snapshot too old error!
1- are using automatic undo mangamanet

The following initialisation parameters can be used to enable and control AUM (do a "show parameters undo" to see your settings):

UNDO_MANAGEMENT (MANUAL or AUTO)
- One MUST set this parameter to AUTO to enable Automatic Undo Management. The default is MANUAL for both Oracle 8i and Oracle 9i databases. One must restart the database to switch between MANUAL and AUTO mode.

UNDO_TABLESPACE (valid UNDO-type tablespace name)
- Specifies which undo tablespace to use.

if you are not using it  see this link in how to set it up
http://www.orafaq.com/node/73

if it is already used then as shajukg said
UNDO_RETENTION (time in seconds)
- Specifies the amount of undo the instance should attempt to retain. The default is 9000 seconds or 15 minutes. If the UNDO tablespace is too small compared to the retention time, one can still get the famous ORA-1555 errors.

UNDO_SUPPRESS_ERRORS (TRUE or FALSE)
- Specifies whether or not to return an exception when DDL and "SET TRANSACTION USE ROLLBACK SEGMENT" statements are issued. The default is FALSE.
 
values for both needs to be reconsidered!

========why do you get old snapshot is because

roll back segments work in a circular fashion by looping around to reuse the extents which have been released by committed transactions. Thus in case of long running queries if data is changed while the query is running, rollback segments created for that change are needed to make a read consistent image for the lon running query. When these extents are reused while these were still need by the query, this error occurs, because oracle can no longer provide a read consistent image of the data.

To avoid this error you need to postpone the reuse of extents. Thus increasing the size of rollback segments and the value of OPTIMAL parameter should do the trick. Comitting less often would be other solution. As until transaction is comitted rollback segment can not be reused thus reducing the chances of a snapshot too old error.

details for how to avoid this issue is in here
http://www.ixora.com.au/tips/admin/ora-1555.htm


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