Database Transactions

This post elaborates on the fundamental concepts of database transactions, ACID compliance, and isolation levels, specifically detailing how Postgres and MySQL implement these features. It explains Postgres's multi-row versioning with `xmin` and `xmax` metadata and the `VACUUM FULL` command for space reclamation, contrasting it with MySQL's undo log approach for consistent reads. The post also defines and illustrates phantom reads, non-repeatable reads, and dirty reads in the context of different isolation levels, and briefly introduces row-level locking in MySQL for concurrent writes.