Elixir Performance Review

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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.

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Elixir Performance Review

Quick Reference

| Issue Type | Reference | |------------|-----------| | Mailbox overflow, blocking calls | references/genserver-bottlenecks.md | | When to use ETS, read/write concurrency | references/ets-patterns.md | | Binary handling, large messages | references/memory.md | | Task patterns, flow control | 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 Do not publish findings until each step passes.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 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, 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.