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9 Replies Latest reply: Dec 10, 2013 1:50 AM by CKPT RSS

Is DG reliable?

petra-K Expert
Currently Being Moderated

Hi all,

 

11.2.0.1

 

We have DG physical standby created for our disaster recovery site. While performing and monitoring this standby db, sometimes I encounter gaps error for archivelogs not created on the standby. For unknown reason it is missing (mostly 1 arch log) but the succeeding logs like 5 or more are waiting or un-applied. To resolve the problem, I then  copy the missing archivelog from Primary to Standby and resume auto recovery.


My question is, what if during this gap issue period, a disaster strike wiping everything our Primary server? So this means I have lots of transaction lost?


Your views and comments are highly appreciated.



Thanks,

pK

  • 1. Re: Is DG reliable?
    Anar Godjaev Expert
    Currently Being Moderated

    Hello,

     

    If in your secondary side 5 or more archivelog gap occurs, for my opinion it is likely network problem. First of all check the network speed between two networks. Then you can see what the problem is in the message column after give select * from v$dataguard_Status; select in secondary side...

     

    Thank you

  • 2. Re: Is DG reliable?
    petra-K Expert
    Currently Being Moderated

    Thanks anar,

     

    I know everybody's network is not perfect and so are the hardware and software. So there will be a time that because of this there will be missing archivelogs and gaps.

    What I say is, even with dataguard you are not guarranteed of 100% no data loss? or even 99%

  • 3. Re: Is DG reliable?
    CKPT Guru
    Currently Being Moderated

    I know everybody's network is not perfect and so it the hardware and software. So there will be a time that because of this there will be missing archivelogs and gaps.

    What I say is, even with dataguard you are not guarranteed of 100% no data loss? or even 99%

    If you do not have good bandwidth/network then it is not really an Oracle issue, Oracle recommends to have good enough badwidth. Even though you have bad bandwidth still you can tune the networking by setting SDU size (Session data unit) so that you can control size of the data you are sending over network.

     

    http://www.oracle.com/technetwork/database/features/availability/maa-wp-10gr2-dataguardnetworkbestpr-134557.pdf

    http://www.oracle.com/technetwork/database/features/availability/dataguardnetwork-092224.html

     

    If you configured in proper way which meets the requirement, YES you can protect.

  • 4. Re: Is DG reliable?
    MahirM.Quluzade Guru
    Currently Being Moderated

    f55237a7-2c38-4db3-a7a3-1d77256f0730 wrote:

     

    Thanks anar,

     

    I know everybody's network is not perfect and so it the hardware and software. So there will be a time that because of this there will be missing archivelogs and gaps.

    What I say is, even with dataguard you are not guarranteed of 100% no data loss? or even 99%

    Hi,

     

    First what is data guard ?
    As you see from name, Data guard is must be guard your data.


    Why  we create a standby database?

    We need create a database contains same data.


    How the standby database is changing when primary  is change?

    Transport service send changes from primary and standby receive this changes and applying to standby database.


    What is protection mode ?

    Protection mode  is depend transport mode of changes. (SYNC, ASYNC)..

     

    When GAP  is occurs and Data  guard is cannot resolve GAP automatically?

    Note :  Maximum protection mode is not occur GAP.


    If your not transported archived logs is deleted or corrupted, then occurs GAP and Data Guard is cannot resolve this GAP automatically.

    If you have this archived logs backups, then restore and wait data guard will transport this archived logs to standby (Apply must be stated)

    if you haven't any backup of this archived logs, then you  must Roll Forward standby database with RMAN incremental backups.

     

    When you cannot resolve GAP?

    If your standby database have GAP , and primary database is failed, corrupted and you cannot recover primary database with  backups.

    If you have GAP and you cannot resolve GAP then it means you  will lost data 100%.

     

     

    Regards

    Mahir M. Quluzade

  • 5. Re: Is DG reliable?
    Anar Godjaev Expert
    Currently Being Moderated

    Hi,

     

    Using of dataguard does not mean that you will not have any data loss in archivelogs. (Oracle supported DataGuard). If you have any GAP and you cannot resolve GAP then it means you  will lost data 100%. (as said Mahir)

     

    Thank you

  • 6. Re: Is DG reliable?
    petra-K Expert
    Currently Being Moderated

    Thanks Chkpt, Mahir, Anar,

     

    TRUE or FALSE.

     

    If you configured in proper way which meets the network requirement, YOU WILL NEVER ENCOUNTER GAPS?

    This means your archivelog transport will always be perfect?


    Has anybody of you not yet encountering gaps?


    Thanks

  • 7. Re: Is DG reliable?
    MahirM.Quluzade Guru
    Currently Being Moderated

    f55237a7-2c38-4db3-a7a3-1d77256f0730 wrote:

     

    Thanks Chkpt, Mahir, Anar,

     

    TRUE or FALSE.

     

    If you configured in proper way which meets the network requirement, YOU WILL NEVER ENCOUNTER GAPS?

    This means your archivelog transport will always be perfect?


    Has anybody of you not yet encountering gaps?


    Thanks

    It is very difficult question, we cannot say what is wait us in the future

    But if your data guard running well and you  monitoring, checking every thing, there haven't any GAP, 

    then we can say you can guard your data with Data Guard technology.

     

    Regards

    Mahir

  • 8. Re: Is DG reliable?
    petra-K Expert
    Currently Being Moderated

    Thanks all,

     

    So the bottomline is....as dba you have to be ready 24/7   to resolve rightaway gaps issues and hoping that disaster will not happen while this gap is occurring.

    This is in a form of LUCK?

  • 9. Re: Is DG reliable?
    CKPT Guru
    Currently Being Moderated

    This is in a form of LUCK?

    No way!!!

    GAP's can encounter either with

    1) Configuration problem (Ex: FAL parameters not set or improper)

    2) netowrk between two sites.

    3) Bugs so that processes will wait at "Arch wait for Sendreq" events

     

    & many..

     

    If you are sure you are confident that you have configured in proper way and network bandwidth is good enough and then better to contact with Oracle support for any bugs, Still those bugs are fixed in higher versions & releases.

    I had similar issues with 11.1/11.2 and many of them fixed in 11.2.0.4 and of course 12c Database as well.

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