Monitoring Performance in Ruby on Rails: A Practical Guide

Ruby on Rails is loved for its productivity and developer happiness. You can move fast, ship features quickly, and iterate with confidence. But as your application grows, performance issues tend to creep in quietly—until one day users complain that “the app feels slow.”

The good news: Rails gives you a lot of signals. The challenge is knowing what to monitor, why it matters, and how to act on it.

This post walks through a pragmatic approach to Rails performance monitoring, from fundamentals to production-ready practices.

Why performance monitoring matters in Rails

Performance problems in Rails rarely come from a single big mistake. More often, they are the result of many small issues:

• An N+1 query added during a harmless refactor
• A background job silently retrying thousands of times
• A memory leak caused by object retention
• A slow SQL query triggered only under specific conditions

Without monitoring, these issues stay invisible. With monitoring, you get early warning signals and clear paths to improvement.

Performance monitoring is not about chasing micro-optimizations. It’s about:

• Protecting user experience
• Keeping infrastructure costs under control
• Making performance regressions obvious and reversible

Core metrics every Rails app should monitor

1. Request performance

At minimum, you should know:

• Request duration (average, p95, p99)
• Slowest endpoints
• Error rate per endpoint

Rails logs already include request timing, but logs alone are hard to aggregate. APM-style tooling makes patterns visible.

Tip: Focus on percentiles, not averages. A fast average can hide a very slow tail.

2. Database performance

For most Rails apps, the database is the bottleneck.

You should track:

• Slow queries
• Query frequency
• Duplicate queries
• Missing or unused indexes

Rails’ ActiveSupport::Notifications emits SQL events automatically. Capturing and analyzing these lets you answer questions like:

• Why is this endpoint slow only in production?
• Which query dominates request time?

High-impact wins often come from indexing and query simplification, not code changes.

3. Background jobs

Background jobs hide performance issues because users don’t see them immediately.

Monitor:

• Job execution time
• Retry counts
• Failures
• Queue latency

A job that runs “only” 500 ms longer than expected can cost real money when executed thousands of times per hour.

4. Memory usage

Rails apps can slowly consume memory due to:

• Object retention
• Caches growing unbounded
• Leaky middleware or gems

You should track:

• RSS over time
• Memory growth per request or job
• Process restarts

Memory issues are often gradual, which makes trend-based monitoring essential.

Going beyond logs: structured performance data

Plain logs answer what happened. Performance monitoring answers why it happened.

The most useful monitoring systems:

• Correlate requests with SQL queries
• Capture execution context (controller, job, user, feature)
• Show trends over time
• Highlight anomalies automatically

This turns performance work from guesswork into diagnosis.

Using Rails internals to your advantage

Rails already gives you powerful hooks:

• ActiveSupport::Notifications for requests, SQL, jobs, cache
• Middleware for request-level instrumentation
• Tagged logging for correlation IDs
• Built-in slow query logging at the database level

A good monitoring setup builds on these primitives instead of fighting them.

Common Rails performance traps (and how monitoring helps)

TrapHow monitoring helpsN+1 queriesShows query count spikes per requestOver-eager background jobsReveals high job volume and retriesInefficient scopesIdentifies slow SQL with call stacksMemory leaksShows steady RSS growthHidden regressionsMakes performance changes visible after deploys

What to look at daily vs weekly

Daily

• Error rate
• Slow requests
• Job failures

Weekly

• Trends in response time
• Top slow queries
• Memory growth patterns

Performance monitoring works best when it’s part of your regular rhythm—not something you check only when things break.

Final thoughts

Rails performance monitoring isn’t about turning Rails into a low-level system. It’s about visibility.

When you can see:

• What’s slow
• Why it’s slow
• When it got slower

…you can fix issues confidently, avoid premature optimization, and keep your Rails app fast as it scales.

If you care about fast, predictable Rails applications, performance monitoring isn’t optional—it’s part of professional Rails development.