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https://issues.apache.org/jira/browse/DERBY-3847?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12625755#action_12625755
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Kim Haase commented on DERBY-3847:
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Hmm -- actually it may be even more confusing because according to the
"Precedence of properties" topic of the tuning guide,
The search order for properties is:
1. System-wide properties set programmatically (as a command-line option to
the JVM when starting the application or within application code)
2. Database-wide properties
3. System-wide properties set in the derby.properties file
So I guess if you had previously set a system-wide property programmatically,
then set it database-wide, then set the database-wide version to null, the
previous programmatic system-wide setting would take effect. If there was none,
the default for the database-wide property would take effect. Or would it?
Would you then slip down to the derby.properties file setting if there was one?
There's also the fact that some properties have *only* system scope or only
database scope.
Maybe rather than try to describe all the permutations, we should just refer
readers to the "Working with Derby properties" section of the tuning guide
(which will actually stay in the tuning guide rather than be moved over to the
Reference Manual when DERBY-2389 is done). What do you think?
> Tuning Guide lacks information on turning off Derby property settings
> ---------------------------------------------------------------------
>
> Key: DERBY-3847
> URL: https://issues.apache.org/jira/browse/DERBY-3847
> Project: Derby
> Issue Type: Bug
> Components: Documentation
> Affects Versions: 10.4.1.3
> Reporter: Kim Haase
> Assignee: Kim Haase
> Priority: Minor
> Attachments: ctunproper22250.html, ctunproper22250.html,
> DERBY-3847-2.diff, DERBY-3847.diff
>
>
> The documentation of how to turn off Derby properties is spotty. Dag Wanvik
> reports that "I checked the code, and when you set a database property to a
> null value, that property is removed from the list of database properties;
> i.e. the situation is back to where you were before it was first set, so the
> built-in defaults apply again (or system properties if there are any)."
> The behavior for turning off user settings is slightly different and is
> documented in several places; it's the general case that seems to be missing.
> This information needs to be added to the description of Derby properties in
> the Tuning Guide, probably in the general topic "Derby properties"
> (http://db.apache.org/derby/docs/dev/tuning/ctunproper22250.html).
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