The following figure illustrates the effects of two contrasting update patterns on the size of a snapshot. As more and more pages are updated in the source database, the size of the file grows. 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. ![]() To store the copied original pages, the snapshot uses one or more sparse files. 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. The same process is repeated for every page that is being modified for the first time. The snapshot stores the original page, preserving the data records as they existed when the snapshot was created. 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. Prerequisites for and Limitations on Database SnapshotsÄatabase snapshots operate at the data-page level. Database snapshots are unrelated to snapshot backups, snapshot isolation of transactions, or snapshot replication.
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