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Add barnes for Heroku Ruby Language Metrics - #7298
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Reports GC/heap/Puma pool stats to HEROKU_METRICS_URL. The Railtie starts it at boot (single mode); a before_worker_boot hook restarts it per worker if Puma runs in cluster mode. Silent no-op outside Heroku. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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What
Adds the
barnesgem (1.0.1) so Heroku's Application Metrics page shows Ruby runtime charts: Puma pool usage, free memory slots, and heap object counts. See Ruby Language Metrics.Gemfile/Gemfile.lock:gem "barnes", "~> 1.0". Barnes 1.0 includes a Railtie that callsBarnes.startat boot, which covers Puma's current single mode (noworkersinconfig/puma.rb).config/puma.rb: abefore_worker_boot { Barnes.start }hook. It only fires in cluster mode (WEB_CONCURRENCY> 1). It's there because the reporter thread doesn't survive a fork. I used this instead of the docs'before_fork, which runs once in the Puma master, not in each worker.Barnes does nothing when
HEROKU_METRICS_URLis unset (local dev, CI) and on one-offrun.*dynos.After merge (manual, in Heroku)
Or turn on Enhanced Language Metrics and Ruby Language Metrics under Metrics → Preferences. These don't work on eco dynos. If the charts are empty after a few minutes, run
heroku run bashand thenBARNES_DEBUG=1 DYNO=web.1 bundle exec pumaand check that the output includespool.capacity.Verified locally
standardrbpasses onGemfileandconfig/puma.rbconfig/puma.rbloads throughPuma::ConfigurationBarnes::Railtieis loaded🤖 Generated with Claude Code