Question

A nightly batch pipeline that processes a queue of jobs from a Postgres `jobs` table used to finish in 20 minutes; since you scaled the workers from 4 to 40 it now takes 3 hours and barely uses CPU. Workers claim jobs with `SELECT ... FROM jobs WHERE status='pending' ORDER BY created_at LIMIT 1 FOR UPDATE`, then update the row. With more workers, throughput went DOWN. `pg_stat_activity` shows most workers blocked on `Lock`. Triage and mitigate.