In my previous post, I showed you how tricky it is to compare objects from the JFR Java API. You probably wondered why I wrote about this topic. Here is the reason: In this blog post, I’ll cover how to load JFR files into a DuckDB database to allow querying profiling data with simple SQL queries, all JFR views included.

This blog post will start a small series on making JFR quack.

TL;DR

You can now use a query tool (via GitHub) to transform JFR files into similarly sized DuckDB files:

> java -jar target/query.jar duckdb import jfr_files/recording.jfr duckdb.db
> duckdb duckdb.db "SELECT * FROM Events";
┌───────────────────────────────┬───────┐
│             name              │ count │
│            varchar            │ int32 │
├───────────────────────────────┼───────┤
│ GCPhaseParallel               │ 69426 │
│ ObjectAllocationSample        │  6273 │

Or run the queries directly, with the database file being cached (if you don’t pass --no-cache), directly supporting all built-in JFR views:

> java -jar target/query.jar query jfr_files/metal.jfr "hot-methods" 
Method                                                                                                   Samples Percent
-------------------------------------------------------------------------------------------------------- ------- -------
java.util.concurrent.ForkJoinPool.deactivate(ForkJoinPool.WorkQueue, int)                                   1066   8.09%
scala.collection.immutable.RedBlackTree$.lookup(RedBlackTree.Tree, Object, Ordering)                         695   5.27%
akka.actor.dungeon.Children.initChild(ActorRef)                                                              678   5.14%

This view is implemented as:

CREATE VIEW "hot-methods" AS
SELECT
  (c.javaName || '.' || m.name || m.descriptor) AS "Method",
  COUNT(*) AS "Samples",
  format_percentage(COUNT(*) / (SELECT COUNT(*) FROM ExecutionSample)) AS "Percent"
FROM ExecutionSample es
JOIN Method m ON es.stackTrace$topMethod = m._id
JOIN Class c ON m.type = c._id
GROUP BY es.stackTrace$topApplicationMethod, c.javaName, m.name, m.descriptor
ORDER BY COUNT(*) DESC
LIMIT 25

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