Elixir Performance Review

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

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 Do not publish findings until each step passes.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.