Rollback segment number not shown with name " not shown " too small

Question

Hi,
we have a table TABLE1 with a BLOB field FIELD1 on a Oracle 10g database. Today we found out that there is one record in that table that make problems. if we try to read the BLOB data from that record, Oracle shows the error:
ORA-01555: snapshot too old: rollback segment number  with name "" too small
The strange thing about it, that the message shows neither the segment number nor the segment's name. Like it has lost the reference to it.
Could you help please.
Notes:
The TABLE1 and the BLOB data are really not big.
The UNDO tablespace is 2Gb big and just 1% used.
Thank you very much
Igor

Answer 1

Out-of-row LOB undo is maintained in the LOB segment. So the UNDO tablespace and undo retention is not associated with most LOB ORA-1555 issues. Instead the LOB column is created using either PCT_VERSION or RETENTION to manage how much space within blocks or time transpires before the LOB undo is overwritten. In environments with high updates, deletes on rows including LOBs, the chances of ORA-1555 on LOB undo is very high.
Source:http://blogs.oracle.com/db/entry/troubleshooting_ora_1555
In the above link you will get plenty of good metalink notes to understand and solve the issue.
There is no undo segment name in the error message means this error has no relation with undo tablespace/parameter/segment. This might mean that your LOB table is corrupted. Can you drop and recreate/re-populate this table and try again ?
Srini Chavali     @ Another "snapshot too old: rollback segment number  with name "" too small"
Regards
Girish Sharma