WordPress database performance audit

Review how query cost, result size, cache behavior, and write amplification scale with production data. Keep this separate from SQL-injection review and from the WP 6.9 salted internal query-cache format.

Audit workflow

1. Inventory queries on each request/worker path, including calls hidden inside metadata and option APIs.
2. Estimate rows matched, rows examined, bytes returned, query count, and how each grows with dataset size.
3. Read the actual core/custom table schema and indexes; do not infer indexes from column names.
4. Inspect representative EXPLAIN plans in a safe environment when available.
5. Trace cache key, miss sentinel, TTL, invalidation, concurrency, and fallback behavior.
6. Rank measured or mechanically demonstrated bottlenecks above style advice.