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From Teja <t...@synapse.ws>
Subject Re: Embedded or Network Framework?
Date Thu, 09 Aug 2007 17:59:38 GMT

Ah, you nailed it for me.. so the documentation changed the definition of JVM
a bit.... Thanks a lot.

John H. Embretsen-3 wrote:
> Teja wrote:
>> Thanks Manjula, John and Bryan; Not very clear yet, but in my situation
>> of a
>> web server( strictly, application server) and a java app (actually a
>> media
>> server app.. serves flash video files basically and lots of other
>> functionality)
>> both on the same machine (and hence only one JVM in its normal
>> definition)
>> where java app loads the web server (web server is shutdown when java app
>> shuts down)
>> ,  so in this situation, I think embedded framework will suffice (as long
>> as
>> the java app 'load's the embedded driver before web server is loaded and
>> none of the web apps try to 'load' the derby embedded driver again.).
>> I think I should be able to simultaneously (from the java app and also
>> from
>> any http requests to the web apps) be able to access/modify same database
>> (will be booted by java app once after the driver is loaded)
>> without any fears of data corruption..
> I think one important thing to be aware of here is what the 
> documentation means when it speaks of a JVM.
> For example, even though you may have only one JDK or JRE installed on 
> your system, you will create a new JVM instance every time you use the 
> "java" command (the command could be something else, depending on JVM 
> vendor etc.). That is, you start a new Java Virtual Machine (JVM) every 
> time you invoke the Java launcher (e.g. "java").
> The last part of the documentation paragraph you quoted in a previous 
> post describes a scenario where the user's Java application accesses the 
> database from one JVM instance (e.g. "java MyApp"). Then, if you try to 
> access the database from another JVM (instance), say the ij tool, you 
> may corrupt the database (but you will most likely be stopped (getting 
> an exception with a warning) before it goes that far).
> In some environments with "complex" classloading this gets a bit more 
> fuzzy, as Bryan mentioned, since the built-in multi-boot prevention 
> mechanisms may be fooled.
> However, having multiple concurrent connections to the same database 
> from the same JVM in a pure embedded framework, is safe.
> In any case you should back up your database regularly, in case 
> something happens.
> Feel free to ask if you have more questions after your try-outs...
> -- 
> John

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