Suggest an editImprove this articleRefine the answer for “What does isolation mean?”. Your changes go to moderation before they’re published.Approval requiredContentWhat you’re changing🇺🇸EN🇺🇦UAPreviewTitle (EN)Short answer (EN)Isolation is a transaction property guaranteeing that concurrent transactions don't see each other's unfinished changes and don't interfere with each other's execution: every transaction should feel like it's "the only one in the system", even when there are actually dozens running. **Key point:** it protects against classic problems like Dirty Read, Non-repeatable Read, and Phantom Read - depending on the isolation level (`Read Committed`, `Repeatable Read`, `Serializable`), where a higher level gives more integrity guarantees at the cost of less concurrency.Shown above the full answer for quick recall.Answer (EN)ImageIsolation is a transaction property that guarantees: **concurrent transactions don't see each other's unfinished changes, and don't interfere with each other's execution**. Every transaction should feel like it's "the only one in the system", even when there are actually dozens running. ### What this means in practice - a transaction **doesn't see intermediate, "dirty" data** from other transactions - concurrent operations **don't produce contradictory results** - the overall effect should look **as if the transactions ran one after another** ### Typical problems without Isolation | Problem | What happens | |---|---| | Dirty Read | reading data from a transaction that hasn't been committed yet | | Non-repeatable Read | reading the same field twice gives different results, because it was changed concurrently | | Phantom Read | a repeated query returns a new set of rows added by another transaction | Isolation protects against exactly these situations, depending on the isolation level. ### Isolation levels (the idea, briefly) Transactional systems have different levels, from faster but less strict, to maximally strict, for example: - `Read Committed` - `Repeatable Read` - `Serializable` (the strictest) The higher the level, the less concurrency, but the more integrity guarantees. ### In one sentence **Isolation = every transaction runs as if it were the only one, and never sees other transactions' unfinished changes.**For the reviewerNote to the moderator (optional)Visible only to the moderator. Helps review go faster.