performance-optimization

# Performance Optimization for Rails 8 ## Overview Performance optimization focuses on: - N+1 query detection and prevention - Query optimization - Memory management - Response time improvements - Database indexing ## Quick Start ```ruby # Gemfile group :development, :test do gem 'bullet' # N+1 detection gem 'rack-mini-profiler' # Request profiling gem 'memory_profiler' # Memory analysis end ``` ## N+1 Query Detection and Prevention N+1 queries occur when code loads a collection then makes a separate query for each associated record. The Bullet gem detects these automatically. Fix them with eager loading via `includes`, `preload`, or `eager_load`. ### Eager Loading Decision Table | Method | Use When | |--------|----------| | `includes` | Most cases (Rails chooses best strategy) | | `preload` | Forcing separate queries, large datasets | | `eager_load` | Filtering on association, need single query | | `joins` | Only need to filter, don't need association data | Key patterns: Bullet configuration, eager loading methods, scoped eager loading, counter caches, N+1 specs with query count assertions. See [references/n-plus-one.md](references/n-plus-one.md) for all code examples and patterns. ## Query Optimization Optimize queries by selecting only needed columns, using batch processing for large datasets, and choosing efficient existence checks. ### Key Patterns | Pattern | Bad | Good | |---------|-----|------| | Column selection | `User.all.map(&:name)` | `User.pluck(:name)` | | Large iterations | `Event.all.each { ... }` | `Event.find_each { ... }` | | Existence checks | `.any?` / `.present?` | `.exists?` | | Collection size | `.length` (loads all) | `.size` (smart) | ### Database Indexing Add indexes for: foreign keys, columns in WHERE/ORDER BY/JOIN clauses, and unique constraints. Use composite indexes for multi-column queries. Use partial indexes for filtered subsets. ### Query Analysis Use `Event.where(...).explain(:analyze)` to inspect query plans. Set up slow query logging via `ActiveSupport::Notifications` to catch queries over a threshold. See [references/query-optimization.md](references/query-optimization.md) for all code examples and patterns. ## Memory Management and Profiling Use `memory_profiler` to detect memory issues. Prefer `pluck` over loading full AR objects, use `find_each` for streaming, and use `update_all` / `in_batches` for bulk operations. ### Rack Mini Profiler Provides per-request profiling in development. Shows query count, timing, and flamegraphs (with `stackprof` gem). Access via the profiler badge or `?pp=flamegraph`. See [references/memory-and-profiling.md](references/memory-and-profiling.md) for all code examples and patterns. ## Quick Fixes Reference | Problem | Solution | |---------|----------| | N+1 on belongs_to | `includes(:association)` | | N+1 on has_many | `includes(:association)` | | Slow COUNT | Add counter_cache | | Loading all columns | Use `select` or `pluck` | | Large dataset iteration | Use `find_each` | | Missing index on FK | Add index on `*_id` columns | | Slow WHERE clause | Add index on filtered column | | Loading unused associations | Remove from `includes` | ## Performance Checklist - [ ] Bullet enabled in development/test - [ ] No N+1 queries in critical paths - [ ] Foreign keys have indexes - [ ] Counter caches for frequent counts - [ ] Eager loading in controllers - [ ] Batch processing for large datasets - [ ] Query analysis for slow endpoints ## Workflow 1. **Detect** -- Enable Bullet, run specs, check Rack Mini Profiler 2. **Analyze** -- Use `explain(:analyze)`, check slow query logs, profile memory 3. **Fix** -- Apply the appropriate pattern from the reference files 4. **Verify** -- Re-run specs, confirm query counts, check profiler ## Reference Files - [references/n-plus-one.md](references/n-plus-one.md) -- N+1 detection, eager loading methods, Bullet config, counter caches, testing patterns - [references/query-optimization.md](references/query-optimization.md) -- Column selection, batch processing, indexing strategies, EXPLAIN analysis, slow query logging - [references/memory-and-profiling.md](references/memory-and-profiling.md) -- Memory profiler usage, memory-efficient patterns, Rack Mini Profiler setup, deployment checklist