Performance Code Review

Analyze this {{language}} code for performance issues:

\`\`\`
{{paste your code}}
\`\`\`

Context: This code runs {{frequency}} (e.g., "on every API request", "in a batch job processing 1M records", "on page load").

Check for:
- Unnecessary allocations or copies
- N+1 query patterns
- Missing caching opportunities
- Algorithmic complexity issues (O(n^2) when O(n) is possible)
- Blocking operations that could be async

For each issue, estimate the impact (high/medium/low) and provide an optimized version. Only flag issues that matter at the stated scale — don't micro-optimize code that runs once.