Re: Oracle database mirroring questions

In addition to Frank's comments, you may also want to explore Oracle Advanced Replication or replication using third party softwares like Quest's Shareplex.

//tc

P.S. NFS is surely a no no

"Frank" <fvanbortel_at_netscape.net> wrote in message news:3EA82E98.1010107_at_netscape.net...
> 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.
>
> Yes - it's actually 'hot', not warm in Oracle speak.
> It's called DataGuard. Real Application Cluster (or RAC) is a cluster
> solution where the crashing of one instance does not affect database
> operations.
>
> > If it does what will be the performance hit (
> > cpu usage ) on the primary because this duplication mechanism is
> > running in the background.
> >
> Low. It will be a low profile file read and transmit to another
> site (Hot Standby).
> None for the RAC solution - although it will have overhead as
> compared to a single instance database.
>
> > 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 reads Oracle internal files (redo log files), that record
> transactions anyway. As such, there's no locking of tables, and
> the application(s) are not affected.
>
http://download-west.oracle.com/docs/cd/B10501_01/server.920/a96524/c01_02in tro.htm#54284
>
> >
> > 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.
>
> Yes - above mentioned RAC
> >
> > 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.
>
> Yes - RAC in combination with a cunning network configuration
>
> >
> > 5. I was of the understanding that Oracle uses raw disk space.
>
> That's an option
>
> > 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.
>
> I have seen Oracle data files reside on journalled file systems,
> logical volumes, and raw devices. All working fine.
> You want all disk performance you can get? Go raw, bypass the OS.
> Want some level of redundancy? Use the file system of your choice.
> >
> > 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.
> >
>
> AFAIK, that is possible but not advised. NAS/SAN seem OK (options
> vary), but NFS has given troubles in the past. Never seen it in use.
> What if the NFS server isn't up?
>
> Don't know if you are hardware bound, or O/S bound, but several
> hardware vendors offer complete RAC solutions. Oracle installed, etc.
> I know (in Europe, at least) that Dell and HP/Compaq deliver such
> solutions for test purposes. Maybe contact your hardware vendor?
> --
> Regards, Frank van Bortel
>
Received on Tue Apr 29 2003 - 17:15:05 CEST