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6 Replies Latest reply: Dec 20, 2010 12:52 AM by 565226 RSS

online redo logs vs standby redo logs

VipinK Newbie
Currently Being Moderated
Hi All,

Oracle version : 10.2.0.4
OS : SunOS 5.10 Generic_118855-36 i86pc i386 i86pc

This might be a silly question for the experts :(

We are having 2 standby databases and 1 logical database. Everything is running fine , I have one confusion : My primary server having 3 online redo log files and 3 standby redo log files (on primary local), but as per the architecture standby redo logs should be on standby server.My question is whether standby redo logs on standby are online redo logs of standby server or standby redo logs of primary server. e.g If i perform a log switch on primary then what is the role of sync and affirm, will lgwr write parallel on online redo logs ,standby redo logs (of primary) or online redo logs (of primary) and online redo logs (which is known as standby redo logs on standby ). Please help me to understand the scenerio.

Thanks in advance!
  • 1. Re: online redo logs vs standby redo logs
    Chinar Guru
    Currently Being Moderated
    You have to refer below docs
    http://download.oracle.com/docs/cd/B19306_01/server.102/b14239/standby.htm#i72373
    http://download.oracle.com/docs/cd/B19306_01/server.102/b14239/create_ps.htm#i1225703
    http://download.oracle.com/docs/cd/B19306_01/server.102/b14239/log_transport.htm#i1235150
  • 2. Re: online redo logs vs standby redo logs
    DBA24*7 Journeyer
    Currently Being Moderated
    The transmission of redo is integral to maintaining the transactional consistency of the primary and standby databases. Both online redo logs and archived redo logs are required in a Data Guard environment.

    A standby redo log provides a number of advantages:

    Standby redo log files can reside on raw devices, which may be important if either or both the primary and standby databases reside in a Real Application Clusters environment.

    Standby redo log files can be multiplexed using multiple members, improving reliability over archived log files.

    During a failover, Data Guard can recover and apply more redo data from standby redo log files than from the archived log files alone.

    The archiver (ARCn) process or the log writer (LGWR) process on the primary database can transmit redo data directly to remote standby redo log files, potentially eliminating the need to register a partial archived log file (for example, to recover after a standby database crashes).
  • 3. Re: online redo logs vs standby redo logs
    DBA24*7 Journeyer
    Currently Being Moderated
    A standby redo log is required to implement below things...

    The maximum protection and maximum availability levels of data protection
    Real-time apply
    Cascaded destinations


    Handle:      VipinK
    Status Level:      Newbie (5)
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    Name      Vipin
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    SO MANY QUESTIONS AND VERY FEW ANSWERS.
  • 4. Re: online redo logs vs standby redo logs
    565226 Newbie
    Currently Being Moderated
    Hi Chinar / Pratham,

    I have a similar query related to standby redo log files:

    In dataguard config, on primary database: we have to create online redo logs & standby redo logs on primary database and on standby database: only online redo log files (no standby redo log files as it would require during switchover/failover).

    My query is that, how oracle will write the data into standby redo log files on standby database (using LNS) , as there is no standby redo log file on standby server.

    Is that mean oracle will write the logs in online redo logs & standby redo logs on primary database and then using LNS transport the standby redo logs on standby database and write into online redo logs of standby database and then archive that log file on standby database.

    Could you please let me clear the concept? I read in doc but not having clarity.
  • 5. Re: online redo logs vs standby redo logs
    DBA24*7 Journeyer
    Currently Being Moderated
    RFS receives redo information from the primary database.
    RFS can write the redo into standby redo logs or directly to archived redo logs. Each LNSn and ARCn process from the primary database has its own RFS process.

    A standby redo log is used only when the database is in the standby role to store redo data received from the primary database. Standby redo logs form a separate pool of log file groups.
    Configuring standby redo log files is highly recommended on all standby databases in a Data Guard configuration, including the primary database to aid in role reversal.

    A standby redo log is required to implement:
    • The maximum protection and maximum availability levels of data protection
    • Real-time apply
    • Cascaded redo log destinations

    Standby redo logs are recommended for maximum performance data protection mode. Unless you are using the real-time apply feature, standby redo logs must be archived before the data can be applied to the standby database. The standby archival operation occurs automatically.
  • 6. Re: online redo logs vs standby redo logs
    565226 Newbie
    Currently Being Moderated
    Hi Pratham,

    Thanks for the reply.

    I think still i did not get the answer of my question. May be i am not able to explain clearly about my doubt. I am trying to explain the scenaio again.

    In Primary database:
    Having 3 online redo logs & 3 standby redo logs

    In Standby database:
    Having 3 online redo logs only (*No standby redo logs*)

    In Primary db:
    During the transaction, it will write in both online redo logs & standby redo logs parallelly and after the log switch, it will instruct the arc to archive the current redo log file in primary database.

    At the same time it will use LNS service to transport the data into standby database.

    In Standby db:
    As per the documentation, RFS service receive the data from primary and write it into standby redo logs before archiving the data.

    Here is my query: +If i am not having any standby redo log on standby database then in which redo log file it will write the data?+

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