Raw SQL when needed in Ruby on Rails - Performance & Optimization

Performance: Raw SQL when needed

MEDIUM IMPACT

This affects database query speed and server response time, impacting how fast data loads on the page.

Fetching complex data with many joins or conditions

Ruby on Rails

User.find_by_sql("SELECT users.*, posts.title FROM users JOIN posts ON posts.user_id = users.id WHERE posts.published = TRUE")

Raw SQL runs a single optimized query directly on the database.

📈 Performance Gainreduces query time by 50-70%, speeds up LCP

Fetching complex data with many joins or conditions

Ruby on Rails

User.joins(:posts).where(posts: { published: true }).select('users.*, posts.title').to_a

ORM generates inefficient SQL causing slow database response.

📉 Performance Costblocks rendering for 100-300ms on complex queries

Performance Comparison

Pattern	DOM Operations	Reflows	Paint Cost	Verdict
ORM complex queries	N/A (server-side)	N/A	Higher due to delayed HTML	[X] Bad
Raw SQL optimized queries	N/A (server-side)	N/A	Lower due to faster HTML	[OK] Good

Rendering Pipeline

Raw SQL affects the server-side data fetching stage before HTML is sent to the browser. Faster queries mean faster HTML generation and quicker first paint.

→Data Fetching

→Server Response

→HTML Rendering

⚠️ BottleneckData Fetching (database query execution)

Core Web Vital Affected

LCP

This affects database query speed and server response time, impacting how fast data loads on the page.

Optimization Tips

1Use raw SQL only for complex queries where ORM is slow.

2Measure query time before switching to raw SQL.

3Keep raw SQL readable and well-documented.

Performance Quiz - 3 Questions

Why might raw SQL improve page load speed compared to ORM queries?

A It runs a single optimized query directly on the database.

B It reduces the number of DOM nodes created.

C It decreases CSS selector complexity.

D It avoids JavaScript parsing.

DevTools: Network

How to check: Open DevTools, go to Network tab, reload page, and check the time for the main document request.

What to look for: Look for shorter server response time indicating faster database queries and HTML generation.