1 Reply Latest reply on Apr 10, 2014 11:51 AM by Tom321

    Redo Log mechanism in Oracle 11g on RAC and ASM

    Ketul Kapadia

      Dear Experts,


      I have my SAP installed on Oracle with RAC and ASM on two nodes. When I take the backup of Redo logs, it takes backup from two threads. Below are the details.


      ARCHIVELOGUNPROTCOARSE06-03-2014 00:0011:00:00 AMthread_1_seq_594.449.841491265257
      ARCHIVELOGUNPROTCOARSE06-03-2014 00:007:00:00 PMthread_1_seq_595.446.84151819567
      ARCHIVELOGUNPROTCOARSE06-03-2014 00:0011:00:00 AMthread_2_seq_627.448.841491265365
      ARCHIVELOGUNPROTCOARSE06-03-2014 00:007:00:00 PMthread_2_seq_628.445.84151819577
      ARCHIVELOGUNPROTCOARSE07-03-2014 00:002:00:00 PMthread_1_seq_596.442.841589007454
      ARCHIVELOGUNPROTCOARSE07-03-2014 00:007:00:00 PMthread_1_seq_597.438.84160583732
      ARCHIVELOGUNPROTCOARSE07-03-2014 00:002:00:00 PMthread_2_seq_629.441.841589065475
      ARCHIVELOGUNPROTCOARSE07-03-2014 00:007:00:00 PMthread_2_seq_630.436.84160583776


      According to the above table, Thread_1 is using the number range 594, 595, 596, 597 and Thread_2 is using 627, 628, 629, 630.


      Question / Doubt : Am I backing the duplicate redo logs i.e. the backup utility is backing up redo logs from Node 1 and Node 2 also.???


      Can anyone explain the mechanism in which the Redo logs are generated in Oracle with RAC and ASM.


      I am new to Oracle so please bear with this question. Customer wants the clarification that the backup of redo logs is fine and no duplicate records are backed up.




        • 1. Re: Redo Log mechanism in Oracle 11g on RAC and ASM

          Hi Ketul,


          in RAC each instance has a separate redo thread, that has it's own sequence number. Yes your backupsoftware IS backing up redologs from both nodes and this is required for RAC. You don't have duplicate archivelogs because of this, each of those files is unique and must be in the backup. If you connect to node 2 your session is generating redo on instance 2, instance 1 doesn't know of this session in its redo logs. If you would e.g. omit the redo logs from instance 2 from your backup, you could not recover the changes done from this (and all other) session on node 2 in case of a crash. The redo logs from node 1 could simply not know of the changes done.