fommil / lions-share

:cat: dev tools for JVM memory problems

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JVM development tools for finding memory and garbage problems.

It can be used as a library - as part of custom regression and performance testing frameworks - or as an sbt plugin to get a report on a main class (or scala App).

Lion's Share produces HTML reports with interactive Google Charts, e.g. shapeless' staging.scala example.

This project is twinned with Shelmet for heap analysis.

SBT Plugin


To use the plugin, add the following to your project's project/plugins.sbt file:

addSbtPlugin("com.github.fommil.lion" % "sbt" % "1.0.0")

Then you may run sbt lion to get a report using the default settings on your project's mainClass.


The full list of settings is best read from the source code of the plugin.

The following are some example settings that can be defined in build.sbt to customise the setup:

lionRuns := 50 // number of times to run the main class (without instrumentation)

lionClass := Some("") // override mainclass just for lions-share

lionOut := new File("my-results") // output directory for lions-share reports and log files

lionAllocRuns := 0 // runs with the allocation agent (slow)

lionAllocTrim := None // no trimming, or trim to this many top-allocated objects

lionAllocRate := 30 // number of seconds to wait between polling the allocation agent.

lionAllocTrace := Map.empty[String, Long] // classes and byte sample threshold


There are some examples under the examples module, including:


To use the Garbage Collection analyser as part of your own testing or analysis framework, you must start your applications with these flags:

-Xloggc:gc.log -XX:+PrintGCDetails -XX:+PrintGCDateStamps -XX:+PrintTenuringDistribution -XX:+PrintHeapAtGC

The GcParser and GcAnalyser classes are then at your disposal, producing a DataTable case class that can be marshalled (using Spray JSON) to the exact form required by Google Charts DataTable class. See GcReporter and the companion report.html for an example.

To use the allocation agent, you must obtain agent-assembly.jar and start your application with

-javaagent:agent-assembly.jar=OUTFILE PERIOD TRACES


  • OUTFILE is the file to write the samples
  • PERIOD is the number of seconds between snapshotting the sampler
  • TRACES is a comma separated list of CLASSNAME:BYTES pairs (optional)

Known Problems

Please check the issue tracker to see if we are already aware of an issue (including a workaround). The biggest issues are;

You might need to run your application under a supported JVM, e.g.:

JAVA_HOME=/opt/jdk1.7.0_51 sbt lion

and if you need really robust garbage collection log parsing, try the commercial product Censum by jClarity.

Planned Features

  1. CPU (instrumentation) sampling
  2. Scala REPL support (e.g. allocation sizes for a block)
  3. non-instrumentation timeseries instance counts