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  1. #1
    Join Date
    Dec 2002
    Posts
    6

    Exclamation Unanswered: Redundant Databases

    Hi,

    I wanna know how I can make to databases reduntant mutually.
    What I want is to have two Oracle servers with same data, and keep both databases active and opened.

    I dont know if its posible. I know I cant create a Standby database, but its not what I want. I need all servers activated.

    Thank you for advanced.
    Regards,

  2. #2
    Join Date
    Sep 2002
    Location
    Ohio
    Posts
    204

    Re: Redundant Databases

    If you want totally independent servers, look into Oracle's Advanced Replication. This can allow both databases to be active and updatable at the same time, but it can involve considerable set-up to achieve this. Pay close attention to conflict detection and resolution.

    You can also use Advanced Replication to make one site updatable and another site read-only. This is a little easier to achieve because you don't have to worry about conflicts.

    If the servers can share disk and can be clustered, look into Oracle's Real Application Clusters.

    HTH,
    Patrick

    Originally posted by Enekyn
    Hi,

    I wanna know how I can make to databases reduntant mutually.
    What I want is to have two Oracle servers with same data, and keep both databases active and opened.

    I dont know if its posible. I know I cant create a Standby database, but its not what I want. I need all servers activated.

    Thank you for advanced.
    Regards,

  3. #3
    Join Date
    Sep 2002
    Location
    ITALY
    Posts
    53

    Re: Redundant Databases

    Originally posted by Enekyn
    Hi,

    I wanna know how I can make to databases reduntant mutually.
    What I want is to have two Oracle servers with same data, and keep both databases active and opened.

    No way out of this choice:
    1) RAC
    2) Adv Rep

    But RAC has a single point of failure in the SAN and/or the DiskArray, and AR have to reconnect to failover to the other db.
    In both the cases the application have to be "aware" that on some errors should not give up but resubmit the work/transaction.

    Simmetric replication has less concerns about conflict resolution if is done in sync; this is the only case in which an app can be rep unaware.
    But if one db fails, you should "manually" bring to a stop the rep process of the surviving db, because in distr. sync transs both can be update or none. After you can plan a service and resilver the rep.

    best regards.
    Franco Ceotto
    SIPTI srl
    OnSite Services
    9i OCP DBA, Performance Engineer

  4. #4
    Join Date
    Dec 2002
    Posts
    6

    Unhappy About Replication

    Hi again.
    I will explain what i want, and what i have now installed.

    I have a Oracle Server. It works with a range between 2 and 30 clients.
    (too easy for Oracle).
    Well, currently i have a Phisical Standby Database as a redundant of the primary server. It works very well, but when I swap roles between both servers (primary to standby and standby to primary) its taken about 2-3 minutes.

    Our system requires commutation between servers to be faster... about 2-3 seconds. This requires than replication must be in 'real time'.

    I'm trying to use Oracle's Advanced Replication, but I think it doesn't work when one of the two servers are down (i.e. for maintenance).

    Then, what I want is two oracle servers replicated, full activated and opened, without lost any data when I shutdown one of them.
    I know its complicated, but easy at the same time.
    I wanna know if Oracle supports this somehow.

    Thanks for advanced!

  5. #5
    Join Date
    Sep 2002
    Location
    ITALY
    Posts
    53

    Re: About Replication

    Originally posted by Enekyn
    Hi again.
    I will explain what i want, and what i have now installed.

    Then, what I want is two oracle servers replicated, full activated and opened, without lost any data when I shutdown one of them.
    I know its complicated, but easy at the same time.
    I wanna know if Oracle supports this somehow.

    Thanks for advanced!
    No data loss is a hard rquirement. You can obtain it with symmetric replication in sync, at the cost of not being able to update data when one of the host is down.
    Moreover the failback to the redundant configuration requires a "resync" of the replication not so easy to do (downtime required).

    Your request are in contradiction: you cannot sync the data you are updating in the opened db with another db that is closed !
    I do not know any system that can let you operate and sync a crashed db; do you ?

    best regards.
    Franco Ceotto
    SIPTI srl
    OnSite Services
    9i OCP DBA, Performance Engineer

  6. #6
    Join Date
    Sep 2002
    Location
    ITALY
    Posts
    53

    Re: About Replication

    Originally posted by franco.ceotto

    Your request are in contradiction: you cannot sync the data you are updating in the opened db with another db that is closed !
    I do not know any system that can let you operate and sync a crashed db; do you ?

    But your requirements, at the far end, can have a costly solution; this idea has come to light whilst I was writing my prev. reply:

    what do you think of having 2 RAC (4 nodes) one replicated on the other, so you can afford a cross downtime of one node per cluster ?

    keep in mind that i never tested this, and so let's know if it works ...

    geetings from italy.
    Franco Ceotto
    SIPTI srl
    OnSite Services
    9i OCP DBA, Performance Engineer

  7. #7
    Join Date
    Dec 2002
    Posts
    6

    Angry More replication...

    Hi again,
    please look at this...

    I need two servers replicated. They can be primary and secondary.. Its not a problem if they can swap roles in a few seconds.

    I want to Server A will be replicated into Server B. Well, if I shutdown Server B, Server A can't replicate. Ok. But I need Server B replicate all the data when it backs on, ok? Can anybody understand me?

    It works with a Physical Standby Database. I can shutdown it, and when I restart it, the data is updated automatically. The problem with this system is than the commutation (swap roles) between servers is too slow. I need it to be faster (abour 2-3 secs).

    Thanks for advanced.

  8. #8
    Join Date
    Sep 2002
    Location
    ITALY
    Posts
    53

    Re: More replication...

    Originally posted by Enekyn
    It works with a Physical Standby Database. I can shutdown it, and when I restart it, the data is updated automatically. The problem with this system is than the commutation (swap roles) between servers is too slow. I need it to be faster (abour 2-3 secs).
    The problem IS the 2-3 secs failover requirement, call it with it's name: syncronous replication.

    And it's a plus the fact that a standby can survive a full-system disaster, including disks, differently from the RAC architecture.
    Franco Ceotto
    SIPTI srl
    OnSite Services
    9i OCP DBA, Performance Engineer

  9. #9
    Join Date
    Dec 2002
    Posts
    6
    Yes, its correct.
    But we cant user a RAC, or clusters.

    We only have to single servers. If one of them suffer a disaster, the other one must be available with all the data. In this case, it can take more time. Its not a problem.
    But when we commutate roles we need to be faster. I think the best option is with two active servers, but the replication is complicated in this case. I think I can do manually, better than Oracle do its.

    Thanks.

  10. #10
    Join Date
    Sep 2002
    Location
    Ohio
    Posts
    204
    Advanced replication should work, but it can be complicated. You are asking for a simple solution to a complex problem. I am not sure you can find that. If it existed, it would be a top seller in the Oracle arena.

    I have a similar situation. It's our company's website. We wanted totally independent databases running at two different sites. We needed to keep them in-synch in near 'Real Time'. I chose Oracle's Advanced Replication. I set up Master-to-Master replication between the two databases, but the application team didn't take the time to consider and design conflict detection and resolution into the database. So, to simplify the Replication set-up and to avoid conflicts, I set the strict guideline that only one of the two databases could ever be updated at a time. I allow read-only connections to the 'secondary' database, but no connections with insert, update or delete access.

    We accomplich this through our application servers. They have been set-up with the 'secondary' database listed as a fail-over for the primary database. They allow connections to only one database at a time. If the primary database fails, the app servers detect it and fail over to the 'secondary' database.

    In this case, the replication set-up was time consuming, but not complex.
    This sounds like it could work for you. Just realize, that under this design, it's the applications job to fail-over to the other database, as the other database is always ready.

    Also, just as an FYI, we have the luxury of being able to replicate changes every ten-seconds without overloading our infrastructure. So, if the first box fails, there will probably be some transactions that have not been propogated to the secondary site. I have to deal with these changes after we recover the primary database. Usually, there are no problems as replication sees that the changes have not been propogated and then propogates them. Once or twice, this has resulted in conflicts, as the data had already been chaged on the other database. I was able to deal with these conflicts manually becuase there were so few of them. Your case may be different.

    There are other products available if you want to avoid Oracle's Advanced replication. Quest has one called SharePlex. I haven't used it, but have heard good things about it.

    HTH,
    Patrick
    Originally posted by Enekyn
    Yes, its correct.
    But we cant user a RAC, or clusters.

    We only have to single servers. If one of them suffer a disaster, the other one must be available with all the data. In this case, it can take more time. Its not a problem.
    But when we commutate roles we need to be faster. I think the best option is with two active servers, but the replication is complicated in this case. I think I can do manually, better than Oracle do its.

    Thanks.

  11. #11
    Join Date
    Aug 2002
    Location
    Paris
    Posts
    1
    You may have another solution with 9.2 standby :

    Pushing archives to standby as MANDATORY with log_archive_dest_n and have a ARCn process to apply them as soon as they are pushed.

    See 9i standby doc for more explanations on this .. (need at least oracle tech network access, check it, its free on technet.oracle.com)

    Documentation on manadatory archive destinations

    And you may use the init.ora parameter known as FAST_START_MTTR_TARGET that precise the number of seconds the database will recover when you open it .. may insure you the 3 seconds needed to open the standby ..

    I didn't checked if it works .. but may be another point of view ..

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