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Re:RE: RE: Stand-by (Oracle9i Data Guard) vs. Replication

From: <dgoulet_at_vicr.com>
Date: Mon, 25 Mar 2002 12:03:52 -0800
Message-ID: <F001.00432779.20020325120352@fatcity.com>


Robert,

    Either way, I do believe that you can't have a standby database in both managed recovery and read only access at the same time which could be your biggest problem. The application would have to understand that under normal circumstances it's getting data from database 'X' and during failures from database 'Y'. This kind of thing gets messy as well. Therefore your best bet is for local objects that are replicated from elsewhere & since all sites can update all data your rather stuck. And as far as the network going down, yours in a similar comment that our network specialist made some 2 years ago, until a back hoe operator ripped out about 1/4 mile of fiber near our building. Took the local yokels 4 days to get it repaired. So don't say 'never' as it definitely can come back to bite you.

Dick Goulet

____________________Reply Separator____________________
Author: "Freeman; Robert " <Robert_Freeman_at_csx.com>
Date:       3/25/2002 2:52 PM

Thanks for your thoughts Dick! Actually, look into Data Guard in 9i and you will find that you are no longer constrained by archive log switches!! I'm really concerned with the conflict resolution issues with MM Replication. I've done something like this once before, with only 2 sites, but it's been so long that it's a hazy distant memory. As I recall, the conflict resolution was a bear.

They are intending on doing the resolution based on a date column and just saying that the latest date winds... they have a method of keeping the date/time on the servers in sync as long as the network is up, but my concern is what happens when it goes down and that date/time sync no longer is working.... or what happens when the system goes down and they also replace the hardware and the date/time is not sync'd for several days until the network is back.

But... then I ask myself how often that will happen too... ;-)

Robert G. Freeman - Oracle8i OCP
Oracle DBA Technical Lead
CSX Midtier Database Administration

The Cigarette Smoking Man: Anyone who can appease a man's conscience can take his freedom away from him.

-----Original Message-----
Sent: Monday, March 25, 2002 2:37 PM
To: Freeman, Robert ; Multiple recipients of list ORACLE-L

Robert,

    Given what you've said it would appear that your only choice is going to be
symetric/advanced replication, multi-master. The conflict resolution rules may
be a bear to set up with 5 sites though. Using a standby db would not be very
effective since data updates are dependent on the archive log switch points and
that does not address the different sites if your reason for failure is a network related one. Snapshots won't work either since they are read only.

Dick Goulet

____________________Reply Separator____________________
Author: "Freeman; Robert " <Robert_Freeman_at_csx.com>
Date:       3/25/2002 9:48 AM

Pretty stringent. They want as little latency as possible. Changes at a master should be available to all sites ASAP. Now, they could all go to one central site, and thats ok as long as our networking is healthy, but if it goes down, there is a requirement that they be able to work independently (there are 4-5 sites) and then all changes need to be synchronized. Data loss is secondary to availability however.

These requirements smack of trouble to me.

Robert G. Freeman - Oracle8i OCP
Oracle DBA Technical Lead
CSX Midtier Database Administration

The Cigarette Smoking Man: Anyone who can appease a man's conscience can take his freedom away from him.

-----Original Message-----
Sent: Monday, March 25, 2002 11:48 AM
To: Multiple recipients of list ORACLE-L

What type of requirement or SLA do you have in regards to keeping the instances in sync?

-Joe


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Received on Mon Mar 25 2002 - 14:03:52 CST

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