Read Committed Snapshot Isolation
When the READ_COMMITTED_SNAPSHOT database option is set to ON, sessions running with the Read Committed isolation mode use row versioning to provide statement-level read consistency. When this database option is enabled and a transaction runs at the Read Committed isolation level, all statements within the transaction see a snapshot of the data as it exists at the start of the statement.
When the READ_COMMITTED_SNAPSHOT option is enabled for a database, SQL Server maintains versions of each row that is modified. Whenever a transaction modifies a row, an image of the row before modification is copied into a page in the version store, which is a collection of data pages in tempdb. If multiple transactions modify ...
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