Tutorial: transactions and ACID properties

Transactions provide a powerful abstraction for multiple threads to operate on data concurrently because they have the following properties:

• Atomicity: all or none of a transaction is completed.
• Consistency: if each transaction maintains some property when considered separately, then the combined effect of executing the transactions concurrently will maintain the same property.
• Isolation: every execution of a transaction is equivalent to one that runs single-threaded.
• Durability: once a transaction is fully complete, changes it made cannot be lost.

These properties greatly simplify the reasoning required for writing concurrent applications. Developers can reason about transactions as if they run single-threaded and independently.

When the data operations in a transaction are complete, the application will normally commit it. This causes it to "take effect." In keeping with the atomicity property, a transaction that fails during execution, or that fails to commit due to a conflict with another running transaction, is then aborted and any changes it may have made are rolled back.