JFR View Command - Sip of Java
Billy Korando on September 26, 2023
The new JFR view command was added in Java 21, providing a way to analyze JFR recordings from the command line without needing to download a recording and open it in a tool like JDK Mission Control. Let’s take a look at how to use the new JFR View command.
Using the JFR View Command
JFR View can be accessed through the jfr command line tool and the jcmd tool.
JFR Tool
JFR View can be used with the jfr tool with the following pattern:
$ jfr view [view] [recording file]
JCMD tool
JFR View can be used with the jcmd tool with the following pattern:
$ jcmd [pid] JFR.view [view]
View Options
Over 70 different view options have been provided with the initial release of the the JFR view command, a number likely to increase in the future. Each view provides different perspectives across the stack from the application level, to the JVM, to the environment.
Java virtual machine views:
class-modifications gc-concurrent-phases longest-compilations
compiler-configuration gc-configuration native-memory-committed
compiler-phases gc-cpu-time native-memory-reserved
compiler-statistics gc-pause-phases safepoints
deoptimizations-by-reason gc-pauses tlabs
deoptimizations-by-site gc-references vm-operations
gc heap-configuration
Environment views:
active-recordings cpu-information jvm-flags
active-settings cpu-load native-libraries
container-configuration cpu-load-samples network-utilization
container-cpu-throttling cpu-tsc recording
container-cpu-usage environment-variables system-information
container-io-usage events-by-count system-processes
container-memory-usage events-by-name system-properties
Application views:
allocation-by-class exception-count native-methods
allocation-by-site file-reads-by-path object-statistics
allocation-by-thread file-writes-by-path pinned-threads
class-loaders finalizers socket-reads-by-host
contention-by-address hot-methods socket-writes-by-host
contention-by-class latencies-by-type thread-allocation
contention-by-site longest-class-loading thread-count
contention-by-thread memory-leaks-by-class thread-cpu-load
exception-by-message memory-leaks-by-site thread-start
exception-by-site modules
A view can be used like this example:
$ jfr view thread-count [recording-file]
Modifying View Output
There are several options to modify the formatting of the data returned from JFR View:
--width [number-of-columns]
--cell-height [number of rows]
--verbose
--truncate beginning
These options need to be provided before the view, like in this example:
$ jfr view --width 40 thread-count recording.jfr
Output:
Java Thread Statistics
Time Acti... Daem... Accu... Peak...
------- ------- ------- ------- -------
21:4... 26 22 145 34
Additional Reading
Happy coding!