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docs: Update flamegraph guide --lines

This commit is contained in:
Eugene Yokota 2025-11-09 18:06:13 -05:00
parent 2b71272c96
commit b17330c9b8
1 changed files with 11 additions and 1 deletions
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12
PROFILING.md
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@ -14,10 +14,11 @@ The first one I recommend is async-profiler. This is available for macOS and Lin
and works fairly well. See their readme for the details, but see the following to get started.
1. Download the installer from <https://github.com/async-profiler/async-profiler/releases/tag/v4.2>
2. Make symbolic link from `asprof` to `$HOME/bin`, assuming you have PATH to `$HOME/bin`:
2. Make symbolic link from `asprof` and `jfrconv` to `$HOME/bin`, assuming you have PATH to `$HOME/bin`:
```bash
$ ln -s $HOME/Applications/async-profiler-4.2/bin/asprof $HOME/bin/asprof
$ ln -s $HOME/Applications/async-profiler-4.2/bin/jfrconv $HOME/bin/jfrconv
```
Next, close all Java applications and anything that may affect the profiling, and run sbt in one terminal:
@ -73,6 +74,15 @@ This should produce `/tmp/flamegraph.html` at the end.
![flamegraph](project/flamegraph.png)
### include line numbers
With Scala, sometimes you would get a method name that looks like `sbt/Defaults$.$init$$anonfun$1`, which we'd have no idea which lambda expression it is pointing to. One workaround is to include the line numbers into the flamegraph by first generating in the Java Flight Recorder format.
```bash
$ asprof -d 60 -f /tmp/flamegraph.jfr <process id>
$ jfrconv --lines /tmp/flamegraph.jfr /tmp/flamegraph.html
```
### running sbt with standby
One of the tricky things you come across while profiling is figuring out the process ID,