Java Reference
In-Depth Information
▪ Nothing specific to JFR, but unifies information from several sources
Garbage collection
▪ Times for GC, including individual phases; sizes of generations
▪ Nothing specific to JFR, but unifies the information from several tools
Profiling
▪ Instrumenting and sampling profiles
▪ Not as much as you'd get from a true profiler, but the JFR profile provides a good
high-order overview
Enabling JFR
In the commercial version of the Oracle JVM, JFR is initially disabled. To enable it, add the
flags -XX:+UnlockCommercialFeatures -XX:+FlightRecorder to the command line of
the application. This enables JFR as a feature, but no recordings will be made until the re-
cording process itself is enabled. That can occur either through a GUI, or via the command
line.
Enabling JFR via Java Mission Control
The easiest way to enable recording is through the Java Mission Control GUI ( jmc ). When
jmc is started, it displays a list of all the JVM processes running on the current system. The
JVM processes are displayed in a tree-node configuration; expand the node under the Flight
Recorder label to bring up the flight recorder window shown in Figure 3-13 .
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