performance-optimization_skill

Overview

This skill identifies and fixes common Rails performance problems such as N+1 queries, slow SQL, and memory bloat. It provides practical fixes: eager loading patterns, indexing guidance, batching, and profiling integration with tools like Bullet and rack-mini-profiler. Use it to improve response times, reduce DB load, and lower memory usage in Rails 8 applications.

How this skill works

The skill inspects controller actions, ActiveRecord usage, and test suites to detect inefficient patterns (N+1, unnecessary selects, full-table loads). It suggests concrete code changes: includes/preload/eager_load, counter_cache migrations, selective select/pluck, batch processing, and appropriate indexes. It also recommends configuration and test hooks for Bullet, rack-mini-profiler, and memory_profiler and helps interpret EXPLAIN output and slow-query logging.

When to use it

• When pages or endpoints are slow or response times regress
• When tests or Bullet report N+1 queries
• When memory usage or GC spikes in console or production
• When database queries are unexpectedly high or slow
• Before deployment to ensure no critical N+1s or missing indexes

Best practices

• Enable Bullet in development and raise in test to catch N+1 early
• Prefer includes and scoped eager loading; use eager_load when filtering on associations
• Use counter_cache for frequent counts and exists? for presence checks
• Select only needed columns or use pluck to avoid AR object overhead
• Process large datasets with find_each or in_batches and prefer update_all for mass updates
• Add indexes for foreign keys, WHERE, ORDER BY, and common JOIN columns

Example use cases

• Fixing an N+1 caused by rendering a list of events with associated venues
• Reducing page load by replacing Event.all.each with Event.find_each and pluck
• Adding a composite index to speed a filtered, paginated query
• Adding Bullet to CI/test so requests fail on N+1 regressions
• Using rack-mini-profiler and flamegraphs to locate slow controller code paths