FAQ
Friends ,
I have a question (sorry if I sound too naive) .

11gR2 manuals say : "The standby redo log must have at least one more redo log group than the redo log at the redo source database, for each redo thread at the redo source database."

It means - we need 3 standby redo log groups on the standby db if there are 2 redo log groups on the primary db . why so ? what is the purpose of that one extra group ?

Regards,
~ JP ~

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  • ZhangLeyi (Kamus) at Sep 26, 2011 at 3:33 am
    Hi Prem

    Incase has no enough time to transfer the redo data from primary to
    standby, plus 1 is more reliable.

    But ... in the real world, if you have network issue, plus 1 will not do
    any help, and if you have perfect network, actually only 1 or 2 standby
    redo log will be used on the standby site.

    So ... IMOHO, you can safely ignore it.

    Prem wrote:
    Friends ,
    I have a question (sorry if I sound too naive) .

    11gR2 manuals say : "The standby redo log must have at least one more redo log group than the redo log at the redo source database, for each redo thread at the redo source database."

    It means - we need 3 standby redo log groups on the standby db if there are 2 redo log groups on the primary db . why so ? what is the purpose of that one extra group ?

    Regards,
    ~ JP ~


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    Zhang Leyi (Kamus) <kamusis@gmail.com>

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  • Prem at Sep 27, 2011 at 6:30 am
    Thanks Maureen , Yong and Kamus . Your replies helped .
    I can think of contention for redo log switch (while db peak hours) on primary but not on standby .If the primary (with all the load) is fine with the no. of redo logs - obviously standby (with less load) should be fine too . I could not think of a good (strong) reason for oracle recommending so . Hope oracle wants us to avoid even the least possibility of getting stuck.

    I just wanted to make sure that I am not missing any good reason for having these extra
    SRL group . Anyway - thanks everyone.

    Regards,
    ~ JP ~
  • Ram Srinivasan at Sep 26, 2011 at 9:41 pm
    Prem: You don't have to follow blindly the manuals. If you have 2 redo log
    groups on the primary, 2 redo log groups on the secondary (standby) will
    suffice.
    Ram Srinivasan
    ================
    On Sat, Sep 24, 2011 at 3:23 AM, Prem wrote:

    Friends ,
    I have a question (sorry if I sound too naive) .

    11gR2 manuals say : "The standby redo log must have at least one more redo
    log group than the redo log at the redo source database, for each redo
    thread at the redo source database."

    It means - we need 3 standby redo log groups on the standby db if there are
    2 redo log groups on the primary db . why so ? what is the purpose of that
    one extra group ?

    Regards,
    ~ JP ~


    --
    http://www.freelists.org/webpage/oracle-l


    --
    Sincerely
    Ram Srinivasan


    --
    http://www.freelists.org/webpage/oracle-l
  • Yong Huang at Sep 27, 2011 at 4:29 pm
    Prem,

    You seem to forget the case where the standby could have inferior hardware, for example slower storage, fewer CPUs, etc., and in case of active data guard, expensive queries. According to my test
    http://www.freelists.org/post/oracle-l/Why-extra-standby-redo-log-group,8
    it *is* possible that the extra SRL becomes active.

    But I think it's only best practice, not requirement.

    Yong Huang

    --- On Tue, 9/27/11, Prem wrote:

    If the primary (with all the load) is fine with the no. of redo logs - obviously standby (with less load) should be fine too .
  • Prem at Sep 28, 2011 at 5:39 am
    True Yong . inferior h/w , active standby with huge load can cause trouble.
    Regards,
    ~ JP ~

    -------------------------------------------------

    Yong Huang wrote :

    Prem,

    You seem to forget the case where the standby could have inferior hardware, for
    example slower storage, fewer CPUs, etc., and in case of active data guard,
    expensive queries. According to my test
    http://www.freelists.org/post/oracle-l/Why-extra-standby-redo-log-group,8
    it *is* possible that the extra SRL becomes active.

    But I think it's only best practice, not requirement.

    Yong Huang

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