1. The Database Layer
80% of performance issues live here. Before you touch Ruby optimizations, ensure your SQL is healthy.
Missing Indexes
Identify slow queries using `pg_stat_statements` or tools like PgHero. Add indexes to foreign keys and columns frequently used in WHERE clauses.
The N+1 Problem
Use the `bullet` gem in development to catch these. Eager load associations using `.includes`, `.preload`, or `.eager_load`.
Select (*) is Evil
Don't load huge text/json columns if you don't need them. Use `.select(:id, :title)` to reduce memory bloat.
2. Ruby & Memory
Ruby is fast enough if you don't allocate thousands of objects per request.
Jemalloc
If you aren't using `jemalloc` with Ruby, you are wasting 30% of your memory. It reduces fragmentation significantly.
Frozen String Literals
Add `# frozen_string_literal: true` to the top of your files to prevent unnecessary string allocations.
3. Background Jobs (Sidekiq)
Move everything you can out of the request cycle.
Idempotency
Jobs will fail and retry. Ensure your jobs can run multiple times without corrupting data.
Argument Size
Don't pass full ActiveRecord objects to jobs. Pass IDs and reload them inside the job (Sidekiq best practice).
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