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From "Rick Hillegas (JIRA)" <derby-...@db.apache.org>
Subject [jira] Commented: (DERBY-1428) Generating derby properties on the fly can lead to non-deterministic engine startup behavior
Date Tue, 20 Jun 2006 21:55:30 GMT
    [ 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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