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data-migration-testing

Skill1 starsChanged 52 days agoMITView on GitHub

Use when testing database schema migrations, system replatforming, or data migrations between systems — pre/post reconciliation, zero-downtime expand/contract, rollback rehearsal, cutover plans, performance of backfills, and data lineage validation.

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  1. Very specific:

    Test both N and N-1 app versions against the intermediate schema.

    line 36

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Files
SKILL.md

Data & Schema Migration Testing

Migrations are one-way doors with production data. Rehearse on production-shaped data, prove reconciliation, and always have a tested rollback.

Plan → rehearse → cut over → verify

  1. Inventory & mapping: source→target field map (type, transform, default, null rule); document lossy conversions & retired fields.
  2. Profile source: row counts, null rates, distinct counts, min/max lengths, orphan FKs, duplicates, bad encodings. Fix or explicitly map anomalies before load.
  3. Rehearse ≥2 times on a masked prod copy: measure duration, lock time, resource use; extrapolate to cutover window.
  4. Reconcile (automated):
    • Counts per table/partition, sum/avg of numeric columns, min/max dates.
    • Row-level hash compare (md5(concat_ws('|', cols))) or sampled diff; keys present in one side only.
    • Referential integrity, unique constraints, sequences/identity next values.
    • Business checks (e.g., open invoices total, active users).
  5. Functional smoke on migrated data through the real app (login, search, reports, exports, APIs).
  6. Rollback rehearsal: restore/reverse and re-verify; know the point of no return.
  7. Cutover runbook with owners, time-stamps, go/no-go gates, comms; freeze writes or use CDC to close the delta.
  8. Post-cutover: monitor errors, slow queries, data-mismatch alerts; keep source read-only for N days.

Zero-downtime schema changes (expand → migrate → contract)

StepChangeSafe?
Expandadd nullable column / new table / index CONCURRENTLYyes
Dual-writeapp writes old+new; backfill in batchesyes
Switch readsflag to new columnyes (rollback = flag)
Contractdrop old column in a later releaseafter soak
Test both N and N-1 app versions against the intermediate schema. Avoid: renaming columns in place, adding NOT NULL without default on large tables, long transactions.

Tools

Flyway/Liquibase/Alembic/Prisma migrate (dry-run + checksum), gh-ost/pt-online-schema-change (MySQL), pg_repack, DMS/Debezium for CDC, datafold/data-diff:

data-diff postgres://old/db orders mysql://new/db orders -k id --columns amount,status
flyway -url=... validate && flyway migrate -dryRunOutput=plan.sql

Edge data to seed

Emoji/Unicode/emoji-in-names, max-length strings, leading zeros, timezone-less timestamps, NULL vs empty string, negative/zero amounts, soft-deleted rows, orphaned children, duplicates, legacy enum values.

Related

database-testing, data-pipeline-etl-testing, compatibility-testing, disaster-recovery-backup-testing, release-readiness-testing

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