Migration planner

Skill IrfanSadiqRahat/constellation/agents/migration-planner

Zero-downtime schema change via expand/contract, dual-write, dual-read.From its SKILL.md

Install

npx -y skills add IrfanSadiqRahat/constellation --skill migration-planner

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SKILL.md

1.6 KB, 391 tokens by cl100k_base, as published. Nobody here has run it

migration-planner

The deliverable: `MigrationPlan`

goal: <one-line change>
phases:
  - id: expand
    actions: <add new schema/columns/index, nullable, no constraint>
    rollback: <drop new>
  - id: dual_write
    actions: <app writes old + new>
    monitor: <consistency check>
  - id: backfill
    chunk_size: <rows>
    rate_limit: <rows/sec>
    progress_metric: <counter>
  - id: dual_read
    actions: <app reads new, falls back to old, alerts on miss>
  - id: switch
    actions: <flip primary read>
  - id: contract
    actions: <drop old>
    waiting_period: <duration after switch>
risks: [<what could go wrong, mitigation>]
abort: <criteria + procedure>
observability: <metrics + alerts during each phase>

Operating principles

Never break and rebuild in the same release. Expand first, contract later.
Backfill is rate-limited. Saturating the primary is a self-inflicted outage.
Constraints come AFTER backfill, with NOT VALID + VALIDATE.
Dual-write must be tested for drift. Periodic reconciliation job.
Switch is feature-flagged. Roll-back is instant.
Contract has a cooling period. Long enough to be confident.
CREATE INDEX CONCURRENTLY always in Postgres.
No ALTER TABLE ... ADD COLUMN ... NOT NULL DEFAULT on large tables. It rewrites.

Hand-off contract

postgres-specialist (or peer) executes. observability-engineer instruments. sre-lead approves the freeze window.

What ships with it

Read from the repository

Just SKILL.md. No reference files, no scripts.