Low-level caching with Rails.cache - Performance & Optimization

Performance: Low-level caching with Rails.cache

HIGH IMPACT

Improves page load speed by storing and reusing expensive data or computations, reducing database queries and server processing time.

Caching expensive database query results to speed up page rendering

Ruby on Rails

def expensive_data
  Rails.cache.fetch('expensive_data_key', expires_in: 10.minutes) do
    Model.where(condition: true).to_a
  end
end

Caches the query result for 10 minutes, serving cached data instantly on repeated requests.

📈 Performance GainReduces database queries to zero during cache lifetime, cutting response time by 80-95%

Caching expensive database query results to speed up page rendering

Ruby on Rails

def expensive_data
  Model.where(condition: true).to_a
end

Runs the database query on every request, causing slow response and high server load.

📉 Performance CostBlocks rendering for 50-200ms per request depending on query complexity

Performance Comparison

Pattern	DOM Operations	Reflows	Paint Cost	Verdict
No caching, query on every request	N/A (server-side)	N/A	N/A	[X] Bad
Using Rails.cache to store query results	N/A (server-side)	N/A	N/A	[OK] Good

Rendering Pipeline

Rails.cache stores data in memory or external stores, so when a request comes, the app can skip expensive data fetching and directly serve cached content, reducing server processing before HTML is sent to the browser.

→Server Processing

→Database Query

→HTML Generation

⚠️ BottleneckDatabase Query and Server Processing

Core Web Vital Affected

LCP

Improves page load speed by storing and reusing expensive data or computations, reducing database queries and server processing time.

Optimization Tips

1Cache expensive queries or computations to reduce server load.

2Use meaningful cache keys and set expiration times to keep data fresh.

3Monitor cache hit rates and response times to ensure caching is effective.

Performance Quiz - 3 Questions

What is the main performance benefit of using Rails.cache for expensive queries?

A Adds extra network requests

B Increases database query frequency

C Reduces server processing time by reusing stored data

D Slows down page rendering

DevTools: Network

How to check: Open DevTools, go to Network tab, reload the page and observe response times and number of requests to the server.

What to look for: Faster response times and fewer database query logs on server indicate effective caching.