ORA-01555: snapshot too old

Question

Hi,
We have audit component, one responsibility of which is to archive audit messages from Oracle database. The component fails on a simple select statement (provided below) that retrieves number of records to be archived based on age parameter:
SELECT COUNT(*) FROM blobobjtable blbt, auditmessagetable msgt WHERE msgt.blobobjtablepk = blbt.blobobjtablepk AND trunc(to_number(substr((SYSTIMESTAMP-msgt.credtimeutc),1,instr(SYSTIMESTAMP-msgt.credtimeutc,' ')))) >= age
We tried the following 3 select statements directly from SQL Plus. The result was that the first two succeeded and the last one failed with "ORA-01555: snapshot too old" exception. We tried these select statements after restart of Oracle database but still got last select statement failed. One thing that we noticed was that the last select statement takes extremely long time to complete. Also, analyzing the index table used during the join failed with the same exception. The same is true when the primary key indices are analyzed.
1) select count(*) from blobobjtable
2) select count(*) from auditmessagetable
3) select count(*) from blobobjtable blbt, auditmessagetable msgt WHERE msgt.blobobjtablepk = blbt.blobobjtablepk
Can somebody explain what might be the cause of ORA-01555 exception for such simple select statement? Does Oracle persists information of UNDO buffers before restart? Is there any way to clean UNDO buffers manually?
If somebody has experience in resolving "ORA-01555: snapshot too old" exception problem please share you experience with us. Any help will be appreciated.
Thanks,
Aleks

Answer 1

how many rows in ur tables.
select count(*) from blobobjtable blbt
SQL> show parameter undo
NAME                                 TYPE        VALUE
undo_management                      string      AUTO
undo_retention                       integer     300
undo_tablespace                      string      UNDOTBS1
SQL> select count(*) from sm;
  COUNT(*)
   1326661
Elapsed: 00:00:03.53
SQL> select count(*) from sm;
  COUNT(*)
   1326661
Elapsed: 00:00:03.45
SQL> select count(*) from sm ss,ac_taj@taj ac
  2  where ss.nserial = ac.nserial;
  COUNT(*)
     88763
Elapsed: 00:00:38.35
SQL> show parameter db_name
NAME                                 TYPE        VALUE
db_name                              string      db02
SQL>i have some configuration of undo tbs. but i am not getting any error. also i am just startup my database if right know i am only one user connected to database.
SQL> select  bytes/1024/1024 "UNTO MB" from dba_data_files
  2  where tablespace_name = 'UNDOTBS1'
  3  /
   UNTO MB
       930