Recovering Online Redo Log Files
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Thread: Recovering Online Redo Log Files

  1. #1
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    Nov 2003
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    Recovering Online Redo Log Files

    Setting up a standby database, manual recovery with Oracle Server Standard 8i:

    Can an online redo log file be stored on an NFS share and if so, is it only recoverable if the database is shutdown properly. I was told that an online redo log file can be applied to a standby database if the primary is still accessible so that's why I'm wondering if its possible to store this files on another server (I understand the database will hang if the network connection is down so the situation is not optimal but it was a question posed to me and I want to make sure I go back with an educated answer). In either case though, are there only certain conditions that the online redo log files are recoverable (ie. only when primary db is shutdown AND shutdown gracefully)? Was also told the way you recover these files is by "recover standby database" and pointing to the online redo log file...I assume once you transfer it over. Thanks

  2. #2
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    Do you understand yourself what the the heck are you talking about?
    One, who thinks that the other one who thinks that know and does not know, does not know either!

  3. #3
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    Angry

    I'm sorry...that is supposed to help me out how? I have been a DBA for all of 2 months now and I'm still learning. I don't know how else to clarify my problem so if there is a specific question you can ask to help me do so, I'd be more than happy to explain.

    Essentially, I have been told I can recover online redo log files on my standby db if I need to failover to it. I've also been told I can do so but "recover standby database" redirecting to the online redo log file. What I'd like to know is:
    a) do I just transfer the current redo file from my primary to my standby and then recover
    b) is it possible to locate these redo files on another server via NFS?
    c) is it even really possible to recover online redo log files on a standby database?

  4. #4
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    Originally posted by jpt6366

    a) do I just transfer the current redo file from my primary to my standby and then recover
    b) is it possible to locate these redo files on another server via NFS?
    c) is it even really possible to recover online redo log files on a standby database?
    a) You never transfer current redo log files anywhere because they are being written into. You transfer archived redo logs.
    b) There is no reason to make online redo logs available via NFS . It serves no purpose.
    c)Standby database does not need online redo logs. Only archived redo logs are being transferred and applied to standby database. If standby database activated, it will create new (own) set of online redo logs.

    I did not want to discourage you from asking a questions, besides I am not a moderator and have no power to restrict you, but I would ask you next time:
    a) Find out as much as you can on your own
    b) Ask your questions in a way that everybody can understand

    Thanks
    One, who thinks that the other one who thinks that know and does not know, does not know either!

  5. #5
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    Nov 2003
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    Understood...its is often difficult to communicate a problem with others when you know what you are talking about.

    a) You never transfer current redo log files anywhere because they are being written into. You transfer archived redo logs.

    Yes, I have a cron job grabbing the archive log files every 20 min. But I specified, in the need of failover I would need to activate the standby. In an effort to recover as much of the primary as possible, I was told the primary's current redo log file can also be recovered onto the standby after primary shutdown but before standby activation. I'd like to know how.

    b) There is no reason to make online redo logs available via NFS . It serves no purpose.

    It was suggested by a non-DBA as a way of preserving the redo logs in the database was destroyed...of course, if the server the redo logs reside on was destroyed...well, I don't even want to think about that.

    c)Standby database does not need online redo logs. Only archived redo logs are being transferred and applied to standby database. If standby database activated, it will create new (own) set of online redo logs.

    Right...but as I mentioned under a) wanted redo logs for recovering as much of primary as possible.

    Just want to know if I am only backed up as far as my latest archive files or can I get anything from the online redo log file as well...and if so, how?

    Thanks for your help

  6. #6
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    Nov 2001
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    Yes, you can. On primary Oracle will read online redo logs after crash and you do not have to worry about it. On a standby site
    just continue to provide file name in a recovery process. Oracle will not know difference between archived and online redo log. The trouble is that you may not always know which online redo log should go next and you may have to try one by one. This will work only you have transferred all your archived redo logs which could be a problem if primary server crashed.
    One, who thinks that the other one who thinks that know and does not know, does not know either!

  7. #7
    Join Date
    Jun 2001
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    Create standby redologs on Standby database , should be of same size and number as u have redlogs on Primary database.(assuming u r using 9i)

  8. #8
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    Nov 2003
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    No, I am using Oracle Server 8i Standard. I have set up a cron job which is successfully transferring and applying archive log files every 20 minutes from the primary to the standby database.

    Are standby redo logs special at all, or can I not just create redo logs on the standby server in the same folders as located on primary server? I assume the location of these redo logs are stored in the data dictionary (system.dbf) and since I have also transferred the data dictionary to the standby, I should have the redo logs set up as they are with the primary.

    For activating the standby database, please verify these steps:

    1) shutdown primary (is shutdown immediate ok?)
    2) transfer primary's current redo log file from primary to standby
    3) recover standby database and indicate the transferred redo log file as the next file to be applied.
    4) activate the standby database

    Please let me know if I've misunderstood or am missing anything. Thanks!!

  9. #9
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    Nov 2001
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    You are missing the fact that you only need to activate standby database in case some kind of emergency and most likely some archived redo logs will be lost which in turns will prevent online redo logs from using.
    What you have described is very well documented by Oracle procedure called Gracefull Switchover. It designed for Oracle 8.1 (I beleive 9i has it built in Data Guard). In case of gracefull switchover when all archived redo logs are available you do not need to activate standby database . Instead you can transfer online redo logs and regenerate control file and you standby database will become primary. Very simular you primary can become standby. It is done so you do not have to invalidate all you backups for any kind of maitenance or DR exercises.
    I guess your steps will work as well.
    Hope it helps
    Last edited by BV1963; 12-16-2003 at 03:55 PM.
    One, who thinks that the other one who thinks that know and does not know, does not know either!

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