Introducing transactions
A transaction is an atomic unit of work that either succeeds or fails. Transactions are a key feature of any database system and are what allows a database to implement the properties: Atomicity, Consistency, Isolation, and Durability (ACID). Altogether, the ACID properties mean that the database must be able to handle units of work whole (atomicity), store data in a permanent way (durability), without inter-mixed changes to the data (consistency), and in a way that concurrent actions are executed as if they were alone (isolation).
You can think of a transaction as a bunch of related statements that, ultimately, will either all succeed or fail. Transactions are everywhere in a database, and you will have already used them even if you did not realize it: function calls, single statements, and so on are executed in a (tiny) transaction block. In other words, every action you issue against the database is executed within a transaction, even if you did not...
