Re: HA options
- From: Seth Miller <sethmiller.sm@xxxxxxxxx>
- To: lambu999@xxxxxxxxx
- Date: Sun, 4 Aug 2013 21:17:09 -0500
Ram,
There is a big difference between HA and DR. If you are looking for zero
downtime for hardware patching, Data Guard (a DR solution) is not going to
help you.
HA can be achieved at a couple of different levels. The most effective
would be a multi-mastered application where you can have multiple
installations that communicate with each other at the application level and
synchronize their changes that way. You will have a global load balancer or
connection pools that will fail over from one installation to another when
it becomes unavailable making it transparent to the clients.
The other level is closer to what you are referring to here; the database
or infrastructure level. Oracle's database clustering solution is called
Real Application Clusters which has a single database that can be accessed
from multiple instances (servers). In the case of RAC, you can bring down
one node of the cluster and the application will continue to run
uninterrupted on the other nodes. This scenario can even be implemented
across data centers (in some cases) and is referred to as a stretched or
extended cluster.
The only other viable solution for true HA is to use a sql apply solution
like GoldenGate (or the deprecated Streams product). GG keeps a secondary
database in sync similar to Data Guard, but the target is open read/write.
In this case, the clients could be trickled over to a secondary database
(be careful with this as you will lose ACID) or failed over all at once
(possible delay and loss of ACID here as well). GG is tricky and requires
an intimate knowledge of the application database architecture.
Seth Miller
On Sun, Aug 4, 2013 at 6:47 PM, Ram K <lambu999@xxxxxxxxx> wrote:
> List,
> As part of minimizing the downtime associated with some critical
> applications, we are exploring the available options. We are planning a
> hardware patch that will require us to shutdown the DBs.
>
> We have a DR site where we can set up dataguard for non clustered
> applications. I was looking into switch over, but it looks like switchover
> needs shutdown and startup and hence there is an associated downtime (twice
> - once switching over to standby and then again switching back). I also
> found some tidbits online where people have complained about delay in
> switching over.
> If there is a smoother way (any such thing as transparent switchover?) with
> dataguard I definitely want to explore the option before checking out other
> options. We have a mix of 10g and 11g. Can the listers share their
> experiences with DG.
>
> --
> Thanks,
> Ram.
>
>
> --
> //www.freelists.org/webpage/oracle-l
>
>
>
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