Hot Sensor Placement

Hot Sensor Placement is a technology used to commit changes to an application's instrumentation during run time without the need to restart the application or application server.

Because of technical limitations, Hot Sensor Placement is only available for Java Virtual Machines.

Changing a sensor's System Profile configuration impacts the application's instrumentation, for example placing a sensor while Agents are connected to the System Profile. The change is not applied immediately. To avoid excessive application restarts, use the Hot Sensor Placement feature, which changes the instrumentation while the application is running.

Sensors that support Hot Sensor Placement are marked with a in the Sensor Placement Section dialog box. If a placed sensor that does not support Hot Sensor Placement () changes, an application restart is required.

Supported JVM versions

Hot Sensor Placement is available for all Agents running under J2SE 5.0 or later. It also applies an Agent Group's Sensor Placement, defined in the activated Configuration, on classes loaded prior to the Configuration change.

JVM support for Hot Sensor Placement

JVM Version Hot Sensor Placement Supported Hot Sensor Placement Enabled Comments
J2SE 1.4.2 no no
Sun(Oracle) J2SE 5.0 or newer yes yes
Sun(Oracle) 1.6.0_14 / 1.6.0_15 no no Both versions contain bugs that prohibit the use of Hot Sensor Placement.
IBM J2SE 5.0 or newer yes no Disabled by default. You can enable it manually in the Agent Mapping Advanced Settings.

If a JVM does not support Hot Sensor Placement, the Agent log indicates that the feature is disabled.

... warning [native] The capability can_redefine_classes was disabled because of a bug in Sun 1.6.0_14 / 1.6.0_15 JVM.
... warning [native] Capability can_redefine_classes not available. Hot Sensor placement is not available in this virtual machine.
... info    [native] Hot Sensor Placement ........ not available

Agents overview

Agents that support Hot Sensor Placement are marked with a badge in the Agents Overview.

Hot Sensor Placement supported/not supported
Hot Sensor Placement supported/not supported

Applying Hot Sensor Placement

Hot Sensor Placement menu
Hot Sensor Placement menu

Use the System Profile context menu to apply Hot Sensor Placement to all Agents of a System Profile at once. To apply it to a single Agent, use the context menu on the Agent in the Agent Overview.

Hot Sensor Placement executes on the method level. All methods on the SUD continue to execute the original code, even during the Hot Sensor Placement, until the Hot Sensor Placement's completion. Methods that start after the Hot Sensor Placement run the new code with the configuration changes applied.


See Configuration Change Immediacy Matrix for more information on available configuration changes and their effects.