RE: Data Guard
- To: <JayMiller@xxxxxxxxxxxxxxxx>, <oracle-l@xxxxxxxxxxxxx>
- Date: Fri, 7 Apr 2006 13:07:45 -0400
I have no idea if this will work, but many naïve DNS caching systems cache only
the first label - that is, if foo.bar has ip 1.2.3.4, it'll cache the mapping
from foo.bar->1.2.3.4 . If, however, foo.bar is a CNAME to bar.baz, and
bar.baz has the IP 1.2.3.4, it might only cache the foo.bar->bar.baz, not the
IP itself. This allows you to change the IP of bar.baz without worrying about
the cache expiry.
Never having worked with either of these programs, I can't say if they'll work,
but I've used this trick before on a very large scale.
Thanks,
Matt
-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx] On
Behalf Of JayMiller@xxxxxxxxxxxxxxxx
Sent: Friday, April 07, 2006 11:48 AM
To: oracle-l@xxxxxxxxxxxxx
Subject: RE: Data Guard
Just an added note if you go the DNS route (which is what we do).
If you use Websphere or Microsoft Transaction Server (or probably most
others) as a middle-tier connection manager then it will be necessary to
recycle the services after the DNS Name is switched since they "thoughtfully"
cache the ip address for you. I remember the first time we did a
primary/standby switch after implementing the middle tier connection pooling
many years ago. I still wake up screaming some nights :)
Oh, if anyone knows a workaround for that I'd love to hear it.
Basically all we ever got out of Oracle or IBM was "just recycle the services
to clear out the cached ip address". It was supposed to be so easy to just
switch the DNS name...
Jay Miller
-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx]
Sent: Friday, April 07, 2006 8:45 AM
To: willyschriemer@xxxxxxxxx
Cc: oracle-l@xxxxxxxxxxxxx
Subject: Re: Data Guard
On 04/07/2006 08:16:22 AM, willy wrote:
> Hi Database Gurus,
>
> I've a question regarding Data Guard. If a database switches role from
> standby to primary can I still connect to the new primary database
without
> setting a network alias or adjusting the tnsnames.ora with the new IP
adress
> ? I guess it has something to do with the tnsnames.ora but I can't
figure
> out how to do this.
>
> TIA,
>
> Willy Schriemer
>
Willy, there are several tricks you can do:
1) Do it on the DNS name server and when the roles are switched, change
the machine alias. That is
the simplest way that requires a little cooperation from SA people.
2) Replace the tnsnames.ora files. That requires either replacing it in
the central location
or re-distributing the new version.
3) You can do it in tnsnames.ora like this:
(FAILOVER=on)
(ADDRESS=
(PROTOCOL=tcp)
(HOST=server1)
(PORT=1521))
(ADDRESS=
(PROTOCOL=tcp)
(HOST=server2)
(PORT=1521))
(CONNECT_DATA=
(SERVICE_NAME=screwup)
Oracle*Net will first try connection to server1 and, if it isn't
available, will
try server2. Trick with DG is that both services (listeners) will
respond, but one
database will be in the recovery mode, unavailable for SQL processing. I
haven't tried
that. You can also add "LOAD_BALANCE=ON" and that will make Oracle*Net
select address at
random. Without that, it will try first address, then the 2nd one and so
forth. You can
also have two database with the same service name and then do this:
SCREWUP_BIG =
DESCRIPTION =
((ADDRESS=
(PROTOCOL=tcp)
(HOST=server1)
(PORT=1521))
(CONNECT_DATA=
(SERVICE_NAME=screwup)
(INSTANCE_ROLE=primary)
(FAILOVER_MODE=
(BACKUP=screwup_small)
(TYPE=select) ))
)
SCREWUP_SMALL =
DESCRIPTION =
((ADDRESS=
(PROTOCOL=tcp)
(HOST=server2)
(PORT=1521))
(CONNECT_DATA=
(SERVICE_NAME=screwup)
(INSTANCE_ROLE=secondary))
)
That will make user connect to the secondary site, in case that the
primary isn't available.
Service names are my own. You would be well advised to change them.
--
Mladen Gogala
http://www.mgogala.com
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