The Four Properties of a Transaction

3116 Words Feb 21st, 2018 12 Pages
Transactions have four properties Atomic, Consistent, Isolated, and Durable. Atomic means that the transaction must occur in its entirety or none of it can occur. If something causes the transaction to fail mid-state, the state of the system cannot be left like it is and must be rolled back to a consistent state. Consistent means that the transaction cannot violate any constraints that have been put in place. An example might be that an integer field with a restriction that the data is greater than 20 cannot be violated. Isolated means a transaction cannot interfere with another transaction. Durable means the transaction is made permanent, usually to a disk, once completed. ACID properties are a main feature of Relational Database Systems. Databases must be consistent and transaction must fall with ACID compliance. If a transaction fails, we would not want the database to commit any of the portions of the transaction that has completed. We also would not want transactions to be stepping on each other during processing. Imagine a retail system with many changes occurring at once, if the changes worked on the same data at once, this may cause issues with the data within the database.

ACID compliance is also a reason that Relational Databases are still much more popular for transaction systems than NoSQL databases. NoSQL databases do not have ACID compliance and there is not the need to since key-value pairs do not really have the same relations of a standard…