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From David Van Couvering <David.Vancouver...@Sun.COM>
Subject Re: [jira] Commented: (DERBY-1428) Generating derby properties on the fly can lead to non-deterministic engine startup behavior
Date Tue, 20 Jun 2006 22:09:53 GMT
I think the issue of derby.system.home and two databases running in the 
same VM is a symptom of a wider problem where I am not convinced we 
actually work running two instances in the same VM.  Derby makes use of 
a lot of system properties; if you have two instances, it seems to me 
that they will always be at war with each other when trying to configure 
Derby.

I would like to bet that if we built a test trying to do this sort of 
thing we would quickly find that it's problematic.  But not actually 
having done this test myself, I can't say for sure.  Has anyone tried this?

David

Rick Hillegas (JIRA) wrote:
>     [ http://issues.apache.org/jira/browse/DERBY-1428?page=comments#action_12416995 ]

> 
> Rick Hillegas commented on DERBY-1428:
> --------------------------------------
> 
> I think this behavior is very puzzling to the system administrator, the end-user, and
tech support. What happens if a system administrator uses one VM to deploy two embedded derby
applications, each of which sets derby.system.home to a different location and/or generates
custom derby.properties? Only one of the applications can win. This kind of behavior is going
to be particularly frustrating if it is intermittent.
> 
> I understand that this behavior may be so central to Derby's operation that we can't
change it. Maybe we could log a warning if we notice that derby.system.home or derby.properties
change within the lifetime of a vm. It would be nice to provide tech support some kind of
tools for identifying this problem.
> 
> Perhaps this is a documentation bug? Maybe the Admin or Developer's Guide should say:
You can code your application this way, but if you do, be aware that it may not play well
with other Derby applications.
> 
>> Generating derby properties on the fly can lead to non-deterministic engine startup
behavior
>> --------------------------------------------------------------------------------------------
>>
>>          Key: DERBY-1428
>>          URL: http://issues.apache.org/jira/browse/DERBY-1428
>>      Project: Derby
>>         Type: Bug
> 
>>   Components: Store
>>     Versions: 10.0.2.0, 10.0.2.1, 10.0.2.2, 10.1.1.0, 10.2.0.0, 10.1.2.1, 10.1.3.0,
10.1.2.2, 10.1.2.3, 10.3.0.0, 10.1.2.4, 10.1.2.5, 10.1.4.0, 10.1.3.1
>>     Reporter: Rick Hillegas
> 
>> A Heisenbug can arise if more than one embedded Derby application runs in the same
VM and at least one of them generates derby properties on the fly. Here's the problem scenario:
>> o The customer runs two embedded Derby apps in the same VM: EmbeddedApp and OtherApp.
>> o EmbeddedApp generates derby properties on the fly before connecting to a database
and triggering engine startup.
>> o Whether the engine picks up those generated properties depends on whether EmbeddedApp
or OtherApp runs first.
>> Here are two workarounds for the problem:
>> 1) Don't generate derby properties on the fly. Instead, specify them on the VM startup
command. Or specify them in a $DERBY_HOME/derby.properties file which is generated before
the VM comes up and which does not change during the lifetime of the VM.
>> 2) If you can't do (1), then modify the VM startup script so that the self-configuring
EmbeddedApp runs first.
> 

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