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From "Gentry, Michael \(Contractor\)" <michael_gen...@fanniemae.com>
Subject RE: Database replication and caching
Date Mon, 31 Jul 2006 16:11:45 GMT
I'm not familiar with PostgreSQL's replication capabilities, but I'd be
concerned about primary key duplication and possible data loss (this
would be outside of Cayenne's control).  For example, what would happen
if both applications ran the sequence to generate PKs at the same time?


-----Original Message-----
From: Borut Bolcina [mailto:bob@najdi.si] 
Sent: Monday, July 31, 2006 11:52 AM
To: cayenne-user
Subject: Database replication and caching


Hello,

I need an advice on using Cayenne in an environment where two PostgeSQL

databases are configured to replicate from each other for failover 
capability. I am thinking of two Cayenne enabled applications (load 
distribution) which insert records in one of those two databases. 
Application one (A1) inserts in database one (DB1) and application two 
(A2) inserts in database two (DB2).

The insertion, deletion or update will cause Java triggers in PostgreSQL

to call appropriate Java method in the application. If for any reason 
one of the databases is down for some time, the replication mechanism 
will bring the second database up-to date which will trigger invocations

of the Java methods, so the second application will be in the correct 
state also.

As long as triggers do not modify records, everything should be ok with 
Cayenne. In case, which I don't foresee now, the records will be 
modified on database level, all DataContexts should be invalidated, am I

right?

Is there any other (caching) problem you see in this architecture?

Regards,
Borut


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