Snapshottiloista

Snapshottiloista, often referred to as snapshot isolation, is a concurrency control mechanism used in database management systems. It is designed to ensure that transactions see a consistent snapshot of the database, preventing issues that can arise from concurrent read and write operations.

In a system employing snapshot isolation, each transaction is provided with a consistent "snapshot" of the database as it existed at the time the transaction began. This means that subsequent modifications made by other transactions are not visible to the transaction operating on the snapshot. This approach simplifies transaction logic for developers as they do not need to worry about seeing intermediate or uncommitted states of the data.

While snapshot isolation prevents many read-related anomalies like dirty reads and non-repeatable reads, it can still suffer from write skew. Write skew occurs when two transactions read overlapping data, make decisions based on those reads, and then write to different data items, leading to an inconsistent state. To detect and handle write skew, systems using snapshot isolation often incorporate mechanisms like optimistic concurrency control. When a write skew is detected, one of the conflicting transactions is typically aborted and restarted.

Snapshot isolation is widely implemented in modern database systems, including PostgreSQL, Oracle, and SQL Server, as it offers a good balance between consistency guarantees and performance. It is a key component in achieving high concurrency without sacrificing data integrity.