/dʊˈrəbɪlɪti/
noun — "changes survive failures permanently."
Durability is a property of transactions in computing and database systems that guarantees once a transaction has been committed, its effects are permanent, even in the event of system crashes, power failures, or hardware malfunctions. This ensures that committed data is never lost and can be reliably recovered, maintaining the integrity of the system over time.
Technically, durability is one of the four ACID properties (Atomicity, Consistency, Isolation, Durability). It is typically implemented through mechanisms such as write-ahead logging, transaction journals, persistent storage, or replication. These mechanisms record the intended changes before applying them, allowing recovery procedures to replay or reconstruct committed operations after failures.
In workflow terms, consider a banking transaction that transfers funds from Account A to Account B. Once the transaction commits, the updated balances are durable: even if the database crashes immediately afterward, recovery processes restore the correct final balances. Durable systems often rely on persistent media like disk drives, SSDs, or distributed replication to ensure long-term reliability.
Durability also extends to distributed systems and cloud storage, where replicated copies across multiple nodes guarantee data survives localized failures. Recovery protocols and consensus algorithms, such as Raft or Paxos, are commonly used to enforce durability in fault-tolerant systems.
Conceptually, durability acts like engraving in stone: once a transaction is recorded and committed, its effects cannot be erased, ensuring consistency and trustworthiness over time.