A JFR analyzer that reads the file for you
Drop in a Java Flight Recorder file and get ranked findings with evidence, instead of a tree you have to explore.
JDK Mission Control will show you everything in a JFR recording, which is the problem — everything is a lot, and most of it is not why your service is slow. flamelens reads the same file and reports the handful of things that account for the time, each with the stacks that prove it.
Wall-clock, not just CPU
The trap in JFR analysis is reading a CPU profile as if it were a latency profile.
- Execution samples and wall-clock time kept distinct
- Blocked and waiting time surfaced separately
- Allocation events read as their own view
Allocation sources named
Garbage collection pressure has a cause, and the cause has a stack.
- Top allocating call sites, ranked
- The finding names the type being allocated
- GC time reported as a share of the recording
A report you can attach to a ticket
Downloadable PDF per report, kept in your history.
- Every report retained on your account
- Shareable with someone who has never opened JMC
Recorded however you like
flamelens does not care how the file was produced.
- `-XX:StartFlightRecording` at startup
- `jcmd JFR.start` against a running JVM
- A recording pulled off a production host
Frequently asked questions
What is in a .jfr file?
A stream of timestamped events the JVM emits: execution samples, allocation events, garbage collections, thread parks, I/O, class loading, and more. It is a recording of what the JVM did, not a snapshot of what it looked like.
How long should I record for?
Long enough to catch the behaviour you are asking about — for a slow endpoint, a few minutes of representative traffic. Longer recordings are not automatically better; they mostly dilute the interesting window.
Can I analyse a recording from production?
Yes, and it is usually the recording worth analysing. JFR's default profile is designed to be cheap enough to leave on.
Do I need JDK Mission Control installed?
No. flamelens parses the file itself; JMC is one way to produce and browse a recording, not a requirement for reading one.
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