squawk

linter for Postgres migrations that prevents downtime for migrations and backwards incompatible changes.

Why?

Prevent unexpected downtime caused by database migrations.

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

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

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://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

dev

cargo install
cargo test
cargo run
cargo clippy -- -W clippy::nursery
cargo fmt

how it works

squawk wraps calls to libpg_query-sys in a safe interface and parses the JSON into eaiser 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.