Postgres Migration Lock Lint

Reads the migration you have open and names every statement that takes a lock Postgres will not share — ACCESS EXCLUSIVE, SHARE, SHARE ROW EXCLUSIVE — and prints the rewrite that does the same thing without stopping traffic.

Works on raw .sql migration files, Rails ActiveRecord::Migration classes, and Django migrations.Migration operation lists.

Why this file and not a linter in CI

An assistant writes a migration in seconds and it reads perfectly. The lock behaviour is not in the text — it is in which Postgres version you are on and which other statement is already running. Four examples from the rule set:

• ADD COLUMN x int DEFAULT 0 is fine on PostgreSQL 11 and later, and rewrites the whole table on 10. The extension does not flag the safe form; a lot of advice still does.
• ADD COLUMN x timestamptz DEFAULT now() is a volatile default, so the fast path does not apply and every row is rewritten under ACCESS EXCLUSIVE.
• SET NOT NULL skips its table scan on PostgreSQL 12 and later only when a validated CHECK (x IS NOT NULL) already exists. Without that constraint it still scans.
• A migration with no lock_timeout is the actual outage: the DDL waits behind one long SELECT, and every query that arrives after the DDL waits behind the DDL. The table is readable, and nothing can read it.

What it reports

36 rules, one message each, naming the lock mode, the failure (Postgres SQLSTATEs 23502, 25001, 42703 where they apply), and the safe rewrite. On the bundled _fixtures/dirty.sql — a 20-statement generated migration — it returns 22 findings: 16 at error severity (writes stop, or the statement aborts) and 6 at warning severity (the statement is instant but breaks the release still running). _fixtures/clean.sql makes the same schema change, split across statements that do not block, and returns 0.

Rule families: index builds (CREATE INDEX, DROP INDEX, REINDEX, CLUSTER), column changes (ADD COLUMN defaults, ALTER COLUMN TYPE, SET NOT NULL, DROP COLUMN, RENAME), constraints (FOREIGN KEY, CHECK, PRIMARY KEY, UNIQUE and the NOT VALID / USING INDEX two-step), transaction shape (CONCURRENTLY inside BEGIN, backfill inside the DDL transaction, missing lock_timeout), data statements (UPDATE/DELETE with no WHERE, TRUNCATE, VACUUM FULL), Rails DSL (add_index, add_reference, change_column, change_column_null, remove_column, rename_column, add_foreign_key, disable_ddl_transaction!), and Django operations (AddIndex, AlterField, RenameField, RemoveField, RunPython, AddIndexConcurrently with atomic = False).

Target: PostgreSQL 12 through 17. PostgreSQL 14 receives its last minor release in November 2026, so the 14 → 17 upgrade window is when most of these statements get written.

Use

Open a migration file and run Postgres Migration Lock Lint: Check this file from the command palette. Findings appear in the Problems panel, on the line that carries the lock.

Free tier: the file you have open, all 36 rules, full messages. Full version ($29 once): every migration in the workspace in one pass, plus the review exported as Markdown or JSON to attach to the change ticket, and an exit-code gate for CI — https://buy.polar.sh/polar_cl_zaJ9pwhlczNQZUXiIKP3wGCzfzxe2LYQ6mMD02xD1j5

The same 36 rules run in the browser, on text you paste, with nothing uploaded: https://getreadystack.com/tools/pg-migration-lock-lint

Yardstick: independent Postgres consultancies bill migration review at $150/hour and up; this is one review, priced once.

Licence

Free tier is unrestricted. The licence key for the full version is validated against the Polar customer portal API; the key check lives in ext/license.js.