RE: Replication Options

  • From: "Mary Bahrami" <mbahrami@xxxxxxxxxxxxxxxx>
  • To: <cjpengel.dbalert@xxxxxxxxx>, <Rajesh.Rao@xxxxxxxxxxxx>
  • Date: Thu, 3 Feb 2005 15:29:38 -0800

> My questions are:
> 1. Does Oracle support LONG datatypes with Advanced Replications in =

v10 does not even have replication in the new EM; it's only in the java =
version of EM now;  Oracle is trying to get us to convert from =
replication to streams....

-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx]On Behalf Of Carel-Jan Engel
Sent: Thursday, February 03, 2005 3:42 PM
To: Rajesh.Rao@xxxxxxxxxxxx
Cc: oracle-l@xxxxxxxxxxxxx
Subject: Re: Replication Options

Hi Rajesh,
On Thu, 2005-02-03 at 18:29, Rajesh.Rao@xxxxxxxxxxxx wrote:

> Hello All,
> We have an application that's presently on on a Solaris 8 box. =
> are  looking to have a DR / Standby site for this database at a remote
> location. Logical Standby database and Advanced replication were ruled =
> because of the use of LONG and LONG RAW datatypes, and the use of =
IOT's by
> the database. So, we decided on a physical standby database.

Right choice. Logical (LSB) isn't that much usable as standby, it's more
for offloading reporting load from your primary. Physical Standby (PSB)
is the way to go for keeping your data safe.

> But now, the requirements change, in that, the user wants a  =
> configuration. In all sense, its a RAC database with nodes at =
> physical locations.  I read, that 10g supports LONG and LONG RAW =
> for Logical standby.

I haven't tested LSB with 10g yet. Don't know whether it has improved a
lot. It's still vulnerable to 'illegal' transactions, which will stop
the SQL Apply proces.

> My questions are:
> 1. Does Oracle support LONG datatypes with Advanced Replications in =

No idea. Advanced Replication adds a whole new dimension when you want
active/active. Either you do it with synchronous replication, and both
databases will stop when one fails, network latency will slow down your
transactions, together with the 2PC, or you do it asynchronously, and
end up with a huge bunch of conflict resolution functions. It will be
hard to manage and might affect your uptime in a negative way.
Of course the users will say that they use perfectly partioned data,
never use/change 'each other's' data and conflicts in the replication
will not occur. Nevertheless, they will occur, sooner (probably) or

> 2. What options do I have? Any third party applications? (Shareplex?)

Is quite expensive.

Requirements for DR stuff is not just a couple of lines. Mostly it takes
some days of discussions and meetings to get them clear. Then you can
decide what requirements are hard and soft. Then options can be

Shareplex is (very) expensive, and not exactly scalable to any level you
might need. Neither is advanced replication. PSB scales quite well,
depending on the log transport options chosen and the network
bandwith/latency. You can think of PSB for DR purposes, and LSB for
offloading reports. Using streams for offloading report work to another
database is another option, maybe even better than LSB.

Keep in mind that Logical Standby and Streams require supplemental
logging. This can affect your amount of redo genereated quite seriously
and thus hurt the performance of your primary database. Furthermore,
some SQL apply processes can do the work in parallel, but it might also
create a serialization point in your replication mechanism, both with
LSB and Streams.

I think the goals to achive need to be specified clearly. They shouldn't
be mixed. HA is not something that comes for free. People tend to try to
make the 'inactive standby' useful somehow. That interferes with the
original requirement. Keep the goals clear and separated.

Best regards,

Carel-Jan Engel

If you think education is expensive, try ignorance. (Derek Bok)

Upcoming appearances:=20

      * Feb 9-10, 2005: Denver, RMOUG Training Days: Data Guard
        Performance Issues    =20
      * Mar 6-10, 2005: Dallas, Hotsos Symposium: Data Guard Performance

> Thanks
> Raj
> --


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