In databases, and transaction processing (transaction management), snapshot isolation is a guarantee that all reads made in a transaction will see a consistent snapshot of the database (in practice it reads the last committed values that existed at the time it started), and the transaction itself will successfully commit only if no updates it has made conflict with any concurrent updates made since that snapshot.
Snapshot isolation has been adopted by several major database management systems, such as InterBase, Firebird, Oracle, MySQL,[1] PostgreSQL, SQL Anywhere, MongoDB[2] and Microsoft SQL Server (2005 and later). The main reason for its adoption is that it allows better performance than serializability, yet still avoids most of the concurrency anomalies that serializability avoids (but not all). In practice snapshot isolation is implemented within multiversion concurrency control (MVCC), where generational values of each data item (versions) are maintained: MVCC is a common way to increase concurrency and performance by generating a new version of a database object each time the object is written, and allowing transactions' read operations of several last relevant versions (of each object). Snapshot isolation has been used[3] to criticize the ANSI SQL-92 standard's definition of isolation levels, as it exhibits none of the "anomalies" that the SQL standard prohibited, yet is not serializable (the anomaly-free isolation level defined by ANSI).
In spite of its distinction from serializability, snapshot isolation is sometimes referred to as serializable by Oracle.
^Multiversion concurrency control in MongoDB, MongoDB CTO: How our new WiredTiger storage engine will earn its stripes
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Berenson, Hal; Bernstein, Phil; Gray, Jim; Melton, Jim; O'Neil, Elizabeth; O'Neil, Patrick (1995), "A Critique of ANSI SQL Isolation Levels", Proceedings of the 1995 ACM SIGMOD international Conference on Management of Data, pp. 1–10, arXiv:cs/0701157, doi:10.1145/223784.223785, ISBN 978-0897917315, S2CID 2316540
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(transaction management), snapshotisolation is a guarantee that all reads made in a transaction will see a consistent snapshot of the database (in practice...
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depends on the isolation level implemented. The most common isolation level implemented with MVCC is snapshotisolation. With snapshotisolation, a transaction...
two-phase locking (SS2PL or Rigorousness). Making snapshotisolation serializable in Snapshotisolation. Global serializability, where the Global serializability...
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About PBXT, About PBXT Inside MarkLogic Server[permanent dead link] SnapshotIsolation in SQL Server "MonetDB Transactions". Retrieved 6 April 2019. Multiversion...
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CTE(Common Table Expressions) and others. 10.0 February 2016 Provides snapshotisolations based on MVCC protocol. Includes many SQL extensions and functions/operators...
serializability are allowed for better performance (e.g., the popular Snapshotisolation mechanism) or to meet availability requirements in highly distributed...
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Wan Shen; Pavlo, Andrew (1 October 2019). "On supporting efficient snapshotisolation for hybrid workloads with multi-versioned indexes". Proceedings of...
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PMC 2850426. PMID 20346436. Schlebusch, CM; Naidoo, T; Soodyall, H (2009). "SNaPshot minisequencing to resolve mitochondrial macro-haplogroups found in Africa"...
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