Summary
In this episode, we explore how transactions and ACID properties ensure data integrity in relational databases. We learn that transactions are units of work that either completely succeed or fail, preventing partial updates that could corrupt data. The four ACID guarantees—Atomicity, Consistency, Isolation, and Durability—work together to keep data safe and reliable, even when multiple operations happen simultaneously. Using examples like flight bookings and money transfers, we see why these properties are critical for systems handling important data, and how databases like Postgres implement them through explicit transaction controls.
Transcript
So far we have seen how relational databases structure and connect data, but structure alone isn't enough. We also need some guarantees that our data stays correct, even if multiple things happen at the same time. And this is where transactions and the ACID properties come in. A transaction is a single unit of work, a set of operations that should either all fail or all succeed. An example can be transferring money between two accounts. We can't allow one side to succeed while the other fails. So we will start a transaction and then once every operation has completed successfully, we finalize it or roll it back if necessary. So you can see here we begin, we update, we update, and then we commit if none of these two operations fail. And we roll back if something goes wrong. ACID is an acronym that describes the four guarantees relational databases aim to provide. We have atomicity, where either the whole transaction happens, or none of it does. There's no half-finished updates. Consistency, where a transaction moves the database between valid states. Constraints, foreign keys, and business rules are always respected. Isolation, where transactions shouldn't interfere with each other. Each one behaves as if it's the only thing that is currently running, even if other things are happening at the same time. Durability, where once a transaction is committed, it's permanent. So even if the database crashes right after the transaction, the data stays. So why does ACID matter? Well, without these guarantees, data would easily become corrupt or inconsistent. Imagine you're booking a flight. If atomicity fails, you can get charged, but you don't have a seat because the operation did not get saved in the database. Two persons can get the same seat if isolation fails. Also, if durability fails, then your booking might disappear after a reboot. Overall, ACID is what makes relational databases safe for critical systems. In Postgres, transactions are built in, and you can explicitly start one with the begin and then end it with either commit or rollback, as we saw in the beginning. The ACID properties define the reliability we expect from a relational database and ensure data integrity and reliability.