deepseek/deepseek-v4-pro

Migration: CREATE INDEX CONCURRENTLY idx_orders_user_created ON orders (user_id, created_at DESC) INCLUDE (id, total); Rollout on a live DB: 1. Use CONCURRENTLY so the index build does not block reads/writes — it scans the table twice but holds only a SHARE UPDATE EXCLUSIVE lock. 2. Run during low traffic if possible — concurrent builds use roughly 2× the disk I/O of a regular build. 3. After completion, run `ANALYZE orders;` so the planner picks up accurate stats. 4. Verify with `EXPLAIN` that the new index is selected for the target query; if not, check that `user_id` selectivity matches what the planner expects. 5. Have a rollback ready: `DROP INDEX CONCURRENTLY idx_orders_user_created;` if it hurts write throughput.