squawk

linter for Postgres migrations

quick start | rules documentation | github integration

Why?

Prevent unexpected downtime caused by database migrations and encourage best practices around Postgres schemas and SQL.

Also it seemed like a nice project to spend more time with Rust.

Install

Note: due to squawk's dependency on libpg_query, squawk only supports Linux and macOS

npm install -g squawk-cli

# or install binaries directly via the releases page
https://github.com/sbdchd/squawk/releases

Usage

❯ squawk example.sql
example.sql:2:1: warning: prefer-text-field

   2 | --
   3 | -- Create model Bar
   4 | --
   5 | CREATE TABLE "core_bar" (
   6 |     "id" serial NOT NULL PRIMARY KEY,
   7 |     "alpha" varchar(100) NOT NULL
   8 | );

  note: Changing the size of a varchar field requires an ACCESS EXCLUSIVE lock.
  help: Use a text field with a check constraint.

example.sql:9:2: warning: require-concurrent-index-creation

   9 |
  10 | CREATE INDEX "field_name_idx" ON "table_name" ("field_name");

  note: Creating an index blocks writes.
  note: Create the index CONCURRENTLY.

example.sql:11:2: warning: disallowed-unique-constraint

  11 |
  12 | ALTER TABLE table_name ADD CONSTRAINT field_name_constraint UNIQUE (field_name);

  note: Adding a UNIQUE constraint requires an ACCESS EXCLUSIVE lock which blocks reads.
  help: Create an index CONCURRENTLY and create the constraint using the index.

squawk --help

squawk
Find problems in your SQL

USAGE:
    squawk [FLAGS] [OPTIONS] [paths]... [SUBCOMMAND]

FLAGS:
    -h, --help
            Prints help information

        --list-rules
            List all available rules

    -V, --version
            Prints version information


OPTIONS:
        --dump-ast <dump-ast>
            Output AST in JSON [possible values: Raw, Parsed]

    -e, --exclude <exclude>...
            Exclude specific warnings

            For example: --exclude=require-concurrent-index-creation,ban-drop-database
        --explain <explain>
            Provide documentation on the given rule

        --reporter <reporter>
            Style of error reporting [possible values: Tty, Gcc, Json]


ARGS:
    <paths>...
            Paths to search


SUBCOMMANDS:
    help                Prints this message or the help of the given subcommand(s)
    upload-to-github    Comment on a PR with Squawk's results

Rules

Individual rules can be disabled via the --exclude flag

squawk --exclude=adding-field-with-default,disallowed-unique-constraint example.sql

See the Squawk website for documentation on each rule with examples and reasoning.

Bot Setup

Squawk works as a CLI tool but can also create comments on GitHub Pull Requests using the upload-to-github subcommand.

Here's an example comment created by squawk using the example.sql in the repo:

sbdchd#14 (comment)

See the "GitHub Integration" docs for more information.

pre-commit hook

Integrate Squawk into Git workflow with pre-commit. Add the following to your project's .pre-commit-config.yaml:

repos:
  - repo: https://github.com/sbdchd/squawk
    rev: v0.10.0
    hooks:
     - id: squawk
       files: path/to/postres/migrations/written/in/sql

Note the files parameter as it specifies the location of the files to be linted.

prior art

• https://github.com/erik/squabble

related tools

• https://github.com/yandex/zero-downtime-migrations
• https://github.com/tbicr/django-pg-zero-downtime-migrations
• https://github.com/3YOURMIND/django-migration-linter
• https://github.com/ankane/strong_migrations

related blog posts / SE Posts / PG Docs

• https://www.braintreepayments.com/blog/safe-operations-for-high-volume-postgresql/
• https://gocardless.com/blog/zero-downtime-postgres-migrations-the-hard-parts/
• https://www.citusdata.com/blog/2018/02/22/seven-tips-for-dealing-with-postgres-locks/
• https://realpython.com/create-django-index-without-downtime/#non-atomic-migrations
• https://dba.stackexchange.com/questions/158499/postgres-how-is-set-not-null-more-efficient-than-check-constraint
• https://www.postgresql.org/docs/10/sql-altertable.html#SQL-ALTERTABLE-NOTES
• https://www.postgresql.org/docs/current/explicit-locking.html
• https://benchling.engineering/move-fast-and-migrate-things-how-we-automated-migrations-in-postgres-d60aba0fc3d4
• https://medium.com/paypal-tech/postgresql-at-scale-database-schema-changes-without-downtime-20d3749ed680

dev

cargo install
cargo run
./s/test
./s/lint
./s/fmt

releasing a new version

1. update the CHANGELOG.md and bump version in the cli Cargo.toml, ensure the lock file is updated, and update package.json and commit the changes

   # update version in Cargo.toml files and package.json to 4.5.3
   s/update-version 4.5.3

2. create a new release on github - CI will attach the binaries automatically

3. wait for build artifacts to be attached to release.

4. login to npm and publish new version.

   npm login
   npm publish

how it works

squawk wraps calls to libpg_query-sys in a safe interface and parses the JSON into easier to work with structures. libpg_query-sys in turn uses bindgen to bind to libpg_query, which itself wraps Postgres' SQL parser in a bit of C code that outputs the parsed AST into a JSON string.

Squawk then runs the rule functions over the parsed AST, gathers and pretty prints the rule violations.