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https://issues.apache.org/jira/browse/DERBY-3424?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12569918#action_12569918
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John H. Embretsen commented on DERBY-3424:
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Here's a summary of my current understanding of (parts of) this feature from
reading the code that is committed so far.
Please correct me if I'm wrong:
- Derby's Management Service is booted regardless of the value of
derby.system.jmx.
- If the VM does not support JMX (meaning: platform management), an
"empty" Management service is booted instead of the "real" one.
- If the value of derby.system.jmx is true, all the current MBeans are
registered with both the platform MBeanServer and Derby's Management
service, and will be available to JMX clients.
- Otherwise (derby.system.jmx is non-true), all the current MBeans except
the ManagementMBean are "registered" with Derby's Management service,
but are not registered with the MBeanServer, and will thus not be
available to JMX clients.
- To enable Derby-JMX at runtime, the JMX client has to create and
register the ManagementMBean with the MBean server, and then invoke
the startManagement() operation.
- Then the MBeans "registered" with Derby's management service are also
automatically registered with the MBean server. This currently only
includes the VersionMBean.
Some questions/comments:
1) Can the Management Service (module) be stopped (I guess this means
permanently disabled) by the user? If so, how?
2) How may/will MBeans such as the JDBCMBean (which are normally
registered e.g. at driver boot time) be registered if JMX management
is disabled at startup of Derby, but enabled later by using the
ManagementMBean?
3) It is slightly confusing that the term "registered" is used both
for MBeans registered with JMX (the MBean server) and for MBeans
instantiated and stored with Derby's Management service. The code needs
to be commented carefully in order to avoid misunderstandings. So far
so good, but I wonder if this might become a problem when more code is
added?
4) In jmxUnregister(), there is a TODO item for error handling, which is
fair enough. Is the associated comment is still valid? If so, I need
some help understanding what "shutdown" means in this context:
} catch (PrivilegedActionException pae) {
// TODO - this is called on shutdown where
// we don't really care about errors.
> Add an MBean that an application can register to change the state of Derby's
> JMX management
> -------------------------------------------------------------------------------------------
>
> Key: DERBY-3424
> URL: https://issues.apache.org/jira/browse/DERBY-3424
> Project: Derby
> Issue Type: New Feature
> Reporter: Daniel John Debrunner
> Assignee: Daniel John Debrunner
> Priority: Minor
>
> JMX in Derby was originally proposed as a mechanism to configure Derby
> replacing or enhancing the system properties which tend to be static in
> nature. Thus it is somewhat ironic that jmx is enabled with a static system
> property derby.system.jmx.
> I propose to add a public mbean that allows the state Derby's JMX management
> to be changed. This bean is not automatically registered by Derby if
> derby.system.jmx is false, but instead can be registered by an application. I
> believe this could occur at any time so that JMX could be enabled on a
> running application, possibly by a remote client.
> This standard Mbean (o.a.d.mbeans.Management & ManagementMBean) would have
> these operations & attribute:
> public boolean isManagementActive();
> public void startManagement();
> public void stopManagement();
> If Derby is not booted within the jvm then the operations would be no-ops.
> If derby.system.jmx is true then Derby will itself register an mbean that
> implements ManagementMBean to allow dynamic control of the visibility of
> Derby's mbeans.
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