rails-37-style-backend-performance

name: rails-37-style-backend-performance description: Preloading, N+1 prevention, memoization license: MIT

Performance Patterns

Database, CSS, and rendering optimizations from 37signals.

CSS Performance

Avoid Complex `:has()` Selectors

Safari freezes on complex nested :has() selectors (#1089). Prefer simpler selectors over clever CSS.

View Transitions

Remove unnecessary view-transition-name causing navigation jank.

Database Performance

N+1 → JOINs

Replace find_each loops with JOINs for bulk operations (#1129).

Accept "unmaintainable" SQL when performance requires it:

"Way way way faster but feels unmaintainable"

Counter Caches

Fast reads, but callbacks are bypassed. Consider manual approach if you need side effects.

Pagination

Start with reasonable page sizes (25-50)
Reduce if initial render is slow (#1089: 50 → 25)
Use "Load more" buttons or intersection observer
Separate pagination per column/section

Active Storage

Read Replicas

Use preprocessed: true - lazy generation fails on read-only replicas (#767)

Slow Uploads

Extend signed URL expiry from default 5 min to 48 hours (#773). Cloudflare buffering can exceed default timeout.

Large Files

Skip previews above size threshold (e.g., 16MB) to avoid timeouts (#941)

Avatars

Redirect to blob URL instead of streaming through Rails
Define thumbnail variants for consistent sizing
Faster than proxying through the app

Rendering Performance

Lazy Loading

Convert expensive menus to turbo frames
Load on interaction, not page load
Reduces initial render time significantly

Debouncing

100ms debounce on filter search feels responsive (#567)

Puma/Ruby Tuning (#1283)

# config/puma.rb
workers Concurrent.physical_processor_count
threads 1, 1

before_fork do
  Process.warmup  # GC, compact, malloc_trim for CoW
end

Use autotuner gem to collect data and suggest tuning.

N+1 Prevention (#1747)

Use prosopite gem for detection. Replace:

# Bad - extra query
assignments.exists? assignee: user

# Good - in-memory
assignments.any? { |a| a.assignee_id == user.id }

Create preloaded scopes:

scope :preloaded, -> {
  includes(:column, :tags, board: [:entropy, :columns])
}

Optimistic UI for D&D (#1927)

Insert immediately, request async:

#insertDraggedItem(container, item) {
  // Insert at correct position respecting priority
  const topItems = container.querySelectorAll("[data-drag-and-drop-top]")
  // ... insert logic
}

await this.#submitDropRequest(item, container)

Batch SQL Over N+1 Loops (#1129)

Replace find_each with JOINs:

# Single query with JOINs instead of N queries
user.mentions
  .joins("LEFT JOIN cards ON ...")
  .joins("LEFT JOIN comments ON ...")
  .where("cards.collection_id = ?", id)
  .destroy_all