Re: Oracle database mirroring questions

On 24 Apr 2003 05:52:03 -0700, sonyantony_at_hotmail.com (Sony Antony) wrote:

>We have been looking at the database redundancy problem from a high
>level point of view, for the purpose of architecturing our distributed
>application. I m not an expert in Oracle. So I decided to ask them
>here before deciding on any particular solution.
>
>1. Does Oracle provide any database replication/mirroring mechanisms,
>so that there will be a warm backup database to take over, if the
>main/primary crashes. If it does what will be the performance hit (
>cpu usage ) on the primary because this duplication mechanism is
>running in the background.
>

Standby database in 8i, dataguard in 9i. Ships redolog (changed bytes). Performance hit should be neglicible.

>2. If such a mechanism as above exists, how does it work. Does it
>duplicate only the modifications of the original database. Does it
>locks the whole tables while it is duplicating the data. Or does it
>lock just the rows - in which case the client applications will not
>'feel' its presence much
>

It just ships the changed bytes by means of net8. NO locking whatsoever is involved.
>3. Does Oracle provide any clustering mechanisms for fault tolerance,
>wherein N number of machines will all have exactly mirrored databases.
>One can afford to lose a number of its node machines. As long as at
>least one node is up all client applications can run without any
>problems.

Parallel server in 8i, RAC in 9i. Transparant Application failover on the client side, provided the client application uses net8
>
>4. Does Oracle provide any clustering mechanisms for load balancing,
>wherein data will not only duplicated among the nodes as 3. above, but
>different clients can connect to different node machines in a load
>balancing fashion, and they will all see the exact same data.
>

Load balancing is included in net8
>5. I was of the understanding that Oracle uses raw disk space. IOW in
>the case of Solaris, it doesn t use the default Solaris UFS file
>system, but uses raw disk space with indexing etc implemented with
>respect to the physical disk location. This makes disk access faster.
>Did I get this wrong. Or is there an option to do it on top of the
>file system or as a raw file system.
>

Only Parallel Server forces you to use RAW disk, unless you have Veritas Database Edition which simulates RAW
>6. One of the possibilities we thought about so as to implement a
>clustering, was to have an NFS server, whose disks are mounted in a
>number of different machines. Each of these machines will run an
>Oracle database server, but accessing the same NFS mounted database.
>Is this possible. I personally didn t think so since if multiple
>machines are modifying the same data at the same time, this will
>result in data corruption, since each machine's modification might not
>be inside a single atomic write() system call.
>
>

It isn't possible, and generally speaking Oracle doesn't endorse and support NFS. It is a crap solution anyway, as NFS is slow and unreliable.

>Thanks a lot for reading.
>--sony

Sybrand Bakker, Senior Oracle DBA

To reply remove -verwijderdit from my e-mail address Received on Thu Apr 24 2003 - 12:17:22 CDT