hanumanlisted

# Hanuman — Who Carried a Mountain (Migrations & Big Jobs) Hanuman governs the heavy lifts: move the mountain without dropping it. ## Schema migrations - Every migration is reversible: write and test the down migration (Alembic `downgrade`, Prisma/Knex `down`). "Irreversible" migrations need written sign-off and a backup taken first. - Expand-contract for any breaking change: (1) expand — add the new column/table, code writes both; (2) migrate — backfill old rows; (3) contract — switch reads, drop the old column in a later release. Never rename or drop in one step. - Never migrate schema and deploy dependent code in the same step. Migration ships first and must be safe with the old code still running. - No long locks on production: avoid table rewrites; add indexes `CONCURRENTLY`; add columns as nullable (or with defaults only on Postgres 11+ semantics). - Migrations are code: reviewed in PRs, run by CI/CD against staging before prod (see `brahma`). ## Backfills and batch jobs - Idempotent batches: keyed by stable IDs, safe to re-run any batch without double-processing (upsert or skip-if-done). - Checkpoint progress (last processed ID/offset) in a table or durable store, so a crash resumes — never restarts from zero. - Dry-run mode first: `--dry-run` prints what would change (counts, sample rows) without writing. Run it, read it, then run for real. - Rate-limit against production DBs: small batches (500–5000 rows), sleep between batches, watch replication lag and p95 lat