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Alejandro Vargas' Blog

  • March 2, 2008

How To Resize the Online Redologs on a RAC Environment

Alejandro Vargas
Technical Leader, ACS Global Delivery, Infrastructure & BigData

Resizing the online redologs on a RAC environment is a simple task, that require a little more attention than that of a single instance.



Usually we do resize when redolog switches happen too frequently. Take care to add all the new larger groups, then switch over until the current redolog for each instance is on the new larger groups before starting to remove the old groups.



You can find a step by step description of the procedure on this document: How to Resize the Online Redologs on a RAC Environment



In some cases it may happen that you have only one instance of the RAC database up:





SQL> select inst_id,thread#,status,enabled,groups,instance,sequence# from gv$thread
/



   INST_ID    THREAD# STATUS ENABLED      GROUPS INSTANCE    SEQUENCE#
---------- ---------- ------ -------- ---------- ---------- ----------
         1          1 CLOSED PUBLIC            3 sati1              41
         1          2 OPEN   PUBLIC            3 sati2              58



You will still see that both threads have a current redolog with status active:





SQL> select inst_id,group#,thread#,sequence#,bytes,members,status from gv$log
  2  /



   INST_ID     GROUP#    THREAD#  SEQUENCE#      BYTES    MEMBERS STATUS
---------- ---------- ---------- ---------- ---------- ---------- ----------------
         1          1          1          0   10485760          2 UNUSED
         1          2          1          0   10485760          2 UNUSED
         1          3          1          0   10485760          2 UNUSED
         1          4          2         59   10485760          2 CURRENT
         1          5          2          0   10485760          2 UNUSED
         1          6          2          0   10485760          2 UNUSED
         1         10          1         39   52428800          2 INACTIVE
         1         11          2         56   52428800          2 INACTIVE
         1         12          1         40   52428800          2 INACTIVE
         1         13          2         57   52428800          2 INACTIVE
        
1         14          1         41   52428800          2 CURRENT
         1         15          2         58   52428800          2 INACTIVE



In this case you will not be able to remove the current group of the thread belonging to the instance that is down until you start the instance and switch over this thread to the new groups; if you try to remove the current group of a down instance you will get the following error:





SQL> alter database drop logfile group 14;
alter database drop logfile group 14
*
ERROR at line 1:
ORA-01623: log 14 is current log for instance sati1 (thread 1) - cannot drop
ORA-00312: online log 14 thread 1: '+DATADG/sati/onlinelog/group_14.303.648232897'
ORA-00312: online log 14 thread 1: '+DATADG/sati/onlinelog/group_14.289.648232903'



 



 





 



 



 

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Comments ( 1 )
  • Santosh Loke Monday, March 17, 2008
    Nice explanation.
    Could you write something on redo recovery in case one of the redo files from either instances is missing?
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