no-column-type-change

What It Detects

ALTER COLUMN TYPE rewrites the entire table under ACCESS EXCLUSIVE lock.

Why It's Dangerous

Changing a column type requires rewriting every row in the table while holding an ACCESS EXCLUSIVE lock. Use the expand-contract pattern: add a new column, backfill, swap.

Bad Example

ALTER TABLE users ALTER COLUMN age TYPE BIGINT;

Good Example

-- Expand-contract pattern:
ALTER TABLE users ADD COLUMN age_new BIGINT;
UPDATE users SET age_new = age;
-- Deploy code to read from age_new
ALTER TABLE users DROP COLUMN age;
ALTER TABLE users RENAME COLUMN age_new TO age;

Configuration

Disable this rule:

# .migrationpilotrc.yml
rules:
  MP007: false

Or change its severity:

# .migrationpilotrc.yml
rules:
  MP007:
    severity: warning