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mihaimurra001mihaimurra001/preConfigProject/.agents/skills/database-and-migrations-architect/SKILL.md

database-and-migrations-architect

Skill1 starsChanged 2 months agoMITView on GitHub

Use when designing schemas, altering tables, writing migrations, or optimizing database queries. Enforces zero-downtime patterns and prevents table locks.

The file

We split this skill into the rules it gives an agent

7 rules. About 0 are common, 5 are distinctive, and 2 are very specific to this project.

  • ≈0

    Common · estimate

    Many files like this have a rule of this kind.

  • ≈5

    Distinctive · estimate

    This author's own choices. Worth a look.

  • 2

    Very specific

    Tied to their project's names, files or tools. Probably skip.

  • Common
  • Distinctive
  • Very specific
  1. Distinctive:

    Follow strict production database engineering practices:

    line 8
  2. Distinctive:

    Phase 1 (Expand): Add new columns as optional (nullable) or with non-locking defaults.

    line 11
  3. Distinctive:

    Phase 3 (Backfill): Run asynchronous background migration jobs in small batches to populate existing rows without exhausting locks or …

    line 13
  4. Distinctive:

    Phase 4 (Contract): Remove old application references, then issue a separate migration to drop old columns.

    line 14
  5. Very specific:

    Never execute ALTER TABLE ...

    line 18
  6. Distinctive:

    Add composite indexes based on query filter selectivity (most selective columns first).

    line 19
  7. Very specific:

    Use partial indexes for boolean flags or soft-deleted rows (WHERE deleted_at IS NULL).

    line 20

≈ “Common” is an estimate: at least 1 in 5 of the 350,495 skill files we read have a rule of the same kind, not the same words. “Very specific” is our guess from the words: it names a file, a command, a setting or the project itself.

Keep what fits and drop the rest. Your version, ready for your agents.
Files
SKILL.md

Database & Zero-Downtime Migrations

Follow strict production database engineering practices:

1. Zero-Downtime Migrations (Expand-and-Contract)

  • Phase 1 (Expand): Add new columns as optional (nullable) or with non-locking defaults. Never drop or rename active columns in the same release.
  • Phase 2 (Dual Write / Dual Read): Application writes to both old and new columns, reads from new column with fallback.
  • Phase 3 (Backfill): Run asynchronous background migration jobs in small batches to populate existing rows without exhausting locks or replication lag.
  • Phase 4 (Contract): Remove old application references, then issue a separate migration to drop old columns.

2. Lock Safety & Indexing

  • In PostgreSQL, always use CREATE INDEX CONCURRENTLY and DROP INDEX CONCURRENTLY.
  • Never execute ALTER TABLE ... ADD COLUMN ... DEFAULT (expensive_function()) on high-traffic tables.
  • Add composite indexes based on query filter selectivity (most selective columns first).
  • Use partial indexes for boolean flags or soft-deleted rows (WHERE deleted_at IS NULL).

3. Query Efficiency & N+1 Prevention

  • Audit ORM queries (Prisma, Drizzle, TypeORM, SQLAlchemy) for sequential loops over foreign relations.
  • Enforce batching with explicit joins, subqueries, or DataLoader patterns.
  • Profile query plans using EXPLAIN (ANALYZE, BUFFERS) before committing complex queries.

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