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Data & Analytics · Advanced

Read Committed Snapshot Isolation (RCSI)

A SQL Server and Azure SQL option that makes Read Committed use row versions, so readers do not block writers.

Definition

With RCSI each statement sees data as of its start, using version rows in tempdb (or the database itself with Accelerated Database Recovery). It is on by default in Azure SQL Database and greatly reduces blocking between readers and writers.

Example

ALTER DATABASE Sales SET READ_COMMITTED_SNAPSHOT ON;

Exam tip

RCSI is the standard fix for reader/writer blocking in SQL Server; it is statement-level, while SNAPSHOT is transaction-level.

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