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Database Snapshots in SQL Server





Database Snapshots in SQL Server


What is DB Snapshot?

Snapshots are read only and are a very good option for reporting purposes. All the reporting related hits could be made on the snapshot instead of on the the actual database, and the burden on the active database could be minimized. Also, as snapshots are read only, chances of any undesired updates by the subscriber (who reads data for reports etc.) could be negated.

A database snapshot is a read-only, static view of a SQL Server database (the source database).It is transactionally consistent with the source database as of the moment of the snapshot's creation and always resides on the same server instance as its source database. As the source database is updated, the database snapshot is updated. Therefore, the longer a database snapshot exists, the more likely it is to use up its available disk space. 

Multiple snapshots can exist on a given source database. Each database snapshot persists until it is explicitly dropped by the database owner. 

Database snapshots operate at the data-page level. Before a page of the source database is modified for the first time, the original page is copied from the source database to the snapshot. The snapshot stores the original page, preserving the data records as they existed when the snapshot was created. The same process is repeated for every page that is being modified for the first time.

 To the user, a database snapshot appears never to change, because read operations on a database snapshot always access the original data pages, regardless of where they reside.
To store the copied original pages, the snapshot uses one or more sparse files. Initially, a sparse file is an essentially empty file that contains no user data and has not yet been allocated disk space for user data. As more and more pages are updated in the source database, the size of the file grows.

Below is the link to code for creating a DB snapshot and also dropping a existing DB snapshot

Create and Drop Snapshot

References:

https://www.codeproject.com/Articles/211100/Database-Snapshot-in-MS-SQL-Server
https://docs.microsoft.com/en-us/sql/relational-databases/databases/database-snapshots-sql-server
 

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