Database Transactions

PlanetScale offers robust transaction management for databases, building upon ACID compliance principles. This includes support for foreign key constraints in unsharded databases, enabling referential integrity while maintaining features like branching and non-blocking schema changes. The system also supports importing existing databases with FKs and provides careful consideration for potential performance degradation. The core of transaction management in PlanetScale is built on the underlying Vitess system, which provides mechanisms for distributed transactions and consistency across shards. The post details how Postgres and MySQL handle transactions, including multi-versioning in Postgres and undo logs in MySQL, and discusses isolation levels (Serializable, Repeatable Read, Read Committed, Read Uncommitted) and their tradeoffs in terms of performance and phenomena like phantom reads, non-repeatable reads, and dirty reads. It also touches on concurrent writes and locking mechanisms.