Sidekiq differs in several key ways:

• Concurrency Model: Sidekiq uses threads (lightweight), while Resque uses processes (heavyweight). DelayedJob can use either.
• Performance: Sidekiq is typically 20x faster than Resque due to threading
• Storage: Sidekiq and Resque use Redis, DelayedJob uses your application's database
• Memory Usage: Sidekiq uses less memory due to threading vs forking
• Dependencies: Sidekiq requires Redis, DelayedJob requires only a database

Example performance difference:

# Sidekiq can process 1000s of jobs/second with one process
# Resque might need 20+ processes for similar throughput