Concurrency vs parallelism

Canonical guidance

• concurrency is about composition and coordination
• parallelism is about simultaneous execution
• a concurrent design may run on one core; a parallel design may still be poorly structured

Use when

• deciding whether goroutines are warranted
• reviewing latency-hiding or pipeline designs
• separating design goals from performance goals

Avoid

• using goroutines as a synonym for optimization
• arguing about scheduler settings before clarifying ownership and cancellation
• adding concurrency to code that is simpler sequentially

Preferred pattern

• first decide the ownership and waiting model, then measure whether parallel execution helps

Anti-pattern

• “make it concurrent” as the whole design rationale

Explanation: This is tempting because goroutines are cheap, but cheap concurrency is still complexity if the problem does not need coordination.

Why

• good concurrent structure and good parallel execution are related but different decisions