Page and action caching in Ruby on Rails - Performance & Optimization

Performance: Page and action caching

HIGH IMPACT

Page and action caching mainly affect how fast the server can respond and how quickly the browser receives fully rendered content.

Serving frequently requested pages quickly

Ruby on Rails

caches_page :show

def show
  @post = Post.find(params[:id])
end

Serves pre-rendered HTML directly from cache without hitting database or rendering views.

📈 Performance GainReduces response time to under 10 ms; saves server CPU cycles

Serving frequently requested pages quickly

Ruby on Rails

def show
  @post = Post.find(params[:id])
  render :show
end

Every request hits the database and renders the view, causing slower response and more server load.

📉 Performance CostBlocks rendering for 100+ ms per request; increases server CPU usage

Performance Comparison

Pattern	DOM Operations	Reflows	Paint Cost	Verdict
No caching, full render each request	High (new DOM each time)	Multiple reflows per request	High paint cost	[X] Bad
Page caching serving static HTML	Low (cached DOM reused)	Single reflow on load	Low paint cost	[OK] Good
Action caching with dynamic cache keys	Medium (cached per param)	Few reflows	Medium paint cost	[!] OK

Rendering Pipeline

Page and action caching bypass the usual server rendering steps by serving stored HTML directly, reducing server processing and speeding up content delivery.

→Server Processing

→Network Transfer

→Browser Rendering

⚠️ BottleneckServer Processing (rendering views and querying database)

Core Web Vital Affected

LCP

Page and action caching mainly affect how fast the server can respond and how quickly the browser receives fully rendered content.

Optimization Tips

1Cache full pages to serve content faster and reduce server load.

2Use dynamic cache keys for actions with variable content to avoid stale data.

3Monitor cache invalidation to maintain content freshness and avoid CLS.

Performance Quiz - 3 Questions

How does page caching improve Largest Contentful Paint (LCP)?

A By reducing CSS file size

B By delaying loading of images until after page load

C By serving pre-rendered HTML directly, reducing server processing time

D By using JavaScript to render content on the client

DevTools: Performance

How to check: Record a page load and look at the 'Main' thread for scripting and rendering time; check if server response time is low.

What to look for: Short server response time and quick first contentful paint indicate effective caching.