Suggest an editImprove this articleRefine the answer for “What does durability mean?”. Your changes go to moderation before they’re published.Approval requiredContentWhat you’re changing🇺🇸EN🇺🇦UAPreviewTitle (EN)Short answer (EN)Durability is a transaction property guaranteeing that once a result is committed, it won't be lost even if a failure occurs: a power outage, a server crash, a process restart, or a system restart. **Key point:** it's achieved through operation logs (a Write-Ahead Log, an oplog), fsync/filesystem journaling, replication, and checkpoints - the system guarantees that changes are written to durable storage, not just held in memory, before confirming the transaction.Shown above the full answer for quick recall.Answer (EN)ImageDurability is a transaction property guaranteeing that **once a result is committed, it won't be lost**, even if a failure occurs: a power outage, a server crash, a process restart, or a system restart. ### What exactly is guaranteed - data that was successfully committed **will definitely reach durable storage** (disk, a log, WAL/oplog, and so on) - after a restart, the database **can restore the committed state** - the data **can no longer roll back**, because the transaction is finished ### How this is achieved technically Different DBMSs implement Durability through: - **operation logs** (a Write-Ahead Log, an oplog) - **fsync / filesystem journaling** - **replication** (in distributed systems) - **checkpoints** The gist is the same: before confirming a transaction, the system **guarantees the changes are written to durable storage**, not just held in memory. ### Example If a transaction transferred money between accounts and returned `commit OK`, then: - even if the server crashes instantly, a second later - after a restart, the data will be in the state it was in at the moment of commit ### The short definition **Durability = "after a commit, the data won't disappear or roll back, the system guarantees it's preserved".** This property closes off the last risk: losing or rolling back changes that were already accepted.For the reviewerNote to the moderator (optional)Visible only to the moderator. Helps review go faster.