cloudthinker-ai Schema Migration Review
Phase 1: Migration Inventory
Document all changes in this migration.
| Change | Table | Column/Index | Operation | Nullable | Default |
|---|---|---|---|---|---|
| ADD/DROP/ALTER/RENAME | Y/N |
Phase 2: Safety Assessment
Lock Analysis:
| Operation | Lock Type | Table Size | Estimated Lock Duration | Acceptable? |
|---|---|---|---|---|
| AccessExclusive/ShareLock/None | Y/N |
Safety Checklist:
- No
ALTER TABLEon large tables without online DDL strategy - No
DROP COLUMNwithout confirming no application reads - No
NOT NULLconstraint added without default value - No full table rewrite on tables >1M rows during peak hours
- No index creation without
CONCURRENTLY(PostgreSQL) or equivalent - Foreign key constraints evaluated for lock implications
- No data type changes that could truncate or corrupt data
Phase 3: Backward Compatibility
Decision Matrix:
| Change Type | Backward Compatible | Strategy |
|---|---|---|
| Add nullable column | Yes | Deploy migration, then code |
| Add non-nullable column with default | Depends on DB | Test lock behavior first |
| Drop column | No | Deploy code ignoring column, then migration |
| Rename column | No | Add new column, migrate data, update code, drop old |
| Change column type | No | Add new column, dual-write, backfill, switch, drop old |
| Add index | Yes (if concurrent) | Deploy anytime |
| Drop index | Yes | Verify no queries depend on it first |
- Application code compatible with both pre- and post-migration schema
- Deployment order documented (code first or migration first)
- Multi-phase migration plan for breaking changes
Phase 4: Rollback Plan
- Rollback migration script exists and tested
- Rollback does not cause data loss
- Rollback can complete within acceptable downtime window
- Rollback has been tested against a copy of production data
Rollback Steps:
- Step description
- Verification after rollback
Phase 5: Execution Plan
- Migration tested against production-size dataset
- Execution time estimated: ___
- Maintenance window required: Y/N
- Application deployment coordination plan
- Monitoring plan during migration
- Communication plan for stakeholders
Pre-execution Checklist:
- Database backup taken
- Replica lag acceptable
- Connection pool capacity sufficient
- Statement timeout configured
- Lock timeout configured
Counter-Rationalizations
| Shortcut | Counter | Why |
|---|---|---|
| "We can skip some steps for this case" | Adapt the workflow steps, don't skip them | Skipped steps are where incidents and oversights originate |
| "The user seems to already know what to do" | Complete all workflow phases with the user | The workflow catches blind spots that experience alone misses |
| "This is a minor case, full process is overkill" | Scale the process down, don't turn it off | Minor cases become major when unstructured; the process scales, not disappears |
| "I'll fill in the details later" | Complete each section before moving on | Deferred details are forgotten; real-time capture is more accurate |
| "The template output isn't necessary" | Always produce the structured output format | Structured output enables comparison, audit trails, and handoff to other teams |
Output Format
Summary
- Migration: ___
- Database: ___
- Risk level: Low / Medium / High / Critical
- Estimated execution time: ___
- Backward compatible: Y/N
- Requires maintenance window: Y/N
Action Items
- Address all safety checklist failures
- Test migration on staging with production-size data
- Test rollback procedure
- Schedule execution window
- Notify affected teams
- Monitor database metrics during and after migration