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From Mike Matrigali <mikem_...@sbcglobal.net>
Subject Re: Asychronous Replication
Date Tue, 10 Apr 2007 20:15:10 GMT


Chabot, Jerry wrote:
> 
> I'm considering options for asynchronous replication. A low cost option 
> is to freeze the source and target databases,
> synchronize the files using rsync (one way) and unfreeze the databases. 
> Freezing is acceptable given the expected
> usage.
> 
> My concern is existing clients of the target database may see stale 
> data. Is there a need to flag the target clients that
> the files have changed?
> 
> Does anyone see any technical issues with this approach?
> 
It won't work.  From the limited description I am assuming you are 
hoping to allow both the source and target to remain open but inactive
during the process.

The state of an open database is maintained by it's in memory cache, 
data files and log files.  If you just copy over data and log from
source to target and then unfreeze the target you have clobbered the
association of the target's in memory cache and the data/log files.

If freezing the target could include shutting down all connections, then
a cheap solution would be to use derby approved backup mechanism to
backup the data files and the logs to the target and then connect to
the backup at the target using a normal connection - which if the 
database had been closed before would allow normal booting of the 
database which would apply the log and bring up a consistent db.  This 
will of course
overwrite everything that was at target.


> -Jerry
> 
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