Support of Java Flight Recorder (JFR)

Java Flight Recorder (JFR) files (.jfr) can be opened in YourKit Java Profiler.

You can analyze JFR recordings by using the powerful features that the profiler provides for its own performance snapshots.

What is shown

Depending on the data contained in the JFR file, the following views are available:

• "CPU" tab:

  • CPU usage and thread count graphs;

  • Profiling results are presented as call trees, method list, hotspots, flame graph basing on recorded jdk.ExecutionSample ("Method profiling sample") events.

    JFR obtains them by sampling.

    Note: the same events are used for CPU usage estimation.

• "Threads" tab:

  All recorded events are shown in a graphical timeline.

• "Memory" tab:

  • The "Memory & GC Telemetry" section shows graphs for:
    • heap and non-heap memory usage;
    • loaded class count;
    • garbage collector statistics (pauses and collection counts);
    • object allocation rate (based on recorded allocation events - see below).
  • The "Allocations" section shows object allocation profiling results basing on recorded allocation events which are jdk.ObjectAllocationInNewTLAB ("Allocation in new TLAB") and jdk.ObjectAllocationOutsideTLAB ("Allocation outside TLAB") for JDK 15 and older, and jdk.ObjectAllocationSample ("Object Allocation Sample") since JDK 16.

• "Monitor usage" tab:

  Blocked and waiting monitor statistics is shown basing on recorded jdk.JavaMonitorEnter ("Java Monitor Blocked") and jdk.JavaMonitorWait ("Java Monitor Wait") events.

• "Exceptions" tab:

  Thrown exception statistics basing on recorded jdk.JavaExceptionThrow ("Java Exception") and jdk.JavaErrorThrow ("Java Error") events.

• "Performance Charts" tab:

  Shows all telemetry graphs in the same place one above the other, with their time axis synchronized.

• "Events" tab:

  This tab presents all recorded events uniformly in a table form, while each other top level tab offers a specialized presentation of particular event types.

• "Summary" tab:

  Profiled process detail and profiling result summary. Also, automatic deobfuscation for an obfuscated profiled code can be configured in this tab.

In graphs, the CPU usage estimation feature is available basing on recordedjdk.ExecutionSample ("Method profiling sample") events. The same event is used for CPU profiling results.

Supported recording file formats

The profiler is able to open any valid .jfr file supported by Java JFR API. This includes files created by the Flight Recorder itself as well as files produced by other tools generating output in this format.

Technically, supported versions are 1.x and 2.x. This includes the majority of use cases.

An attempt to open an unsupported file version results in the error: "File version 0.9. Only Flight Recorder files of version 1.x and 2.x can be read by this JDK."

There are a few known cases when an unsupported version file is produced:

• Java Flight Recorder of Oracle JDK Java 8 produces recording files of version 0.9. The JFR is a commercial feature in this JDK and requires the Java option -XX:+UnlockCommercialFeatures to unlock.

  As a workaround, use OpenJDK Java 8 which produces compatible recording files.

  Alternatively, use Java 11 or newer. Any OpenJDK or Oracle JDK produce compatible recording files.

• Older versions of Async Profiler ("async-profiler") produce .jfr files of version 0.9. To solve the problem, upgrade to Async Profiler 2.0 or newer.