/elixir-performance-review

name: elixir-performance-review
description: Reviews Elixir code for performance issues including GenServer bottlenecks, memory usage, and concurrency patterns. Use when reviewing high-throughput code or investigating performance issues.

Elixir Performance Review

Quick Reference

| Issue Type | Reference | |------------|-----------| | Mailbox overflow, blocking calls | [references/genserver-bottlenecks.md](references/genserver-bottlenecks.md) | | When to use ETS, read/write concurrency | [references/ets-patterns.md](references/ets-patterns.md) | | Binary handling, large messages | [references/memory.md](references/memory.md) | | Task patterns, flow control | [references/concurrency.md](references/concurrency.md) |

Review Checklist

GenServer

• [ ] Not a single-process bottleneck for all requests
• [ ] No blocking operations in handle_call/cast
• [ ] Proper timeout configuration
• [ ] Consider ETS for read-heavy state

Memory

• [ ] Large binaries not copied between processes
• [ ] Streams used for large data transformations
• [ ] No unbounded data accumulation

Concurrency

• [ ] Task.Supervisor for dynamic tasks (not raw Task.async)
• [ ] No unbounded process spawning
• [ ] Proper backpressure for message producers

Database

• [ ] Preloading to avoid N+1 queries
• [ ] Pagination for large result sets
• [ ] Indexes for frequent queries

Valid Patterns (Do NOT Flag)

• **Single GenServer for low-throughput** - Not all state needs horizontal scaling
• **Synchronous calls for critical paths** - Consistency may require it
• **In-memory state without ETS** - ETS has overhead for small state
• **Enum over Stream for small collections** - Stream overhead not worth it

Context-Sensitive Rules

| Issue | Flag ONLY IF | |-------|--------------| | GenServer bottleneck | Handles > 1000 req/sec OR blocking I/O in callbacks | | Use streams | Processing > 10k items OR reading large files | | Use ETS | Read:write ratio > 10:1 AND concurrent access |

Gates — before reporting

Do these **in order** for the performance review. Do not publish findings until each step passes.

1. **Protocol loaded** — Read [review-verification-protocol](../review-verification-protocol/SKILL.md) and apply its checks for each finding (hot paths, concurrency, resource use). **Pass:** For every substantive finding, you can name which protocol subsection you satisfied or state **N/A** with reason (e.g. pure reference to this skill’s Valid Patterns). 2. **Anchored evidence** — **Pass:** Each finding includes a concrete locator: `path:line` (or line range), or `Module.function/arity` plus a short quoted snippet from the file. 3. **Performance claims** — For anything under [Context-Sensitive Rules](#context-sensitive-rules), or any claim of bottleneck, N+1, unbounded growth, or heavy memory/binary cost, **Pass:** You state the **observed or measured** fact that meets “Flag ONLY IF” (e.g. rate, item count, ratio), or attach an artifact (profiler output, SQL/log excerpt, `grep`/search scope)—otherwise downgrade to **question** / **suspected** with what was not verified.

Before Submitting Findings

Complete **Gates — before reporting** (section above) first; the verification protocol is mandatory input to those gates.