A database snapshot in SQL Server is a read-only, static view of the database (the source database).
The database snapshot is transactionally consistent with the source database at the time of snapshot production.
A database snapshot is always saved on the same server instance as the source database.
While database snapshots provide a read-only view of the data in the state it was in at the time the snapshot was created, the snapshot file grows in size as changes are made to the source database.
It is possible to create several snapshots of a source database. Each database snapshot is permanent until it is voluntarily deleted by the database owner.
Read on to learn even more about snapshots in SQL servers.
An In-Depth Look At Snapshots
Database snapshots are performed from data page by data page.
The original page is transferred from the source database to the snapshot prior to the first update of a page in the source database.
The snapshot preserves the original page, preserving all data records in their original state at the moment the snapshot was created.
The same approach is repeated for each page that is modified for the first time.
Because read operations on a database snapshot always access the original data pages, regardless of their location, they appear to be unchanged to the user.
The snapshot stores the replicated original pages in one or more sparse files. A sparse file is a file that does not include any user data and has not yet been allotted disc space for user data.
The file grows in size as the number of pages modified in the source database rises.
Benefits Of Snapshots
There are several benefits of snapshotting your data. Here are the best reasons why it should be done:
- Reports may be generated using snapshots.
- Clients can query a database snapshot, allowing for the creation of reports based on the data included in the snapshot at the time the snapshot was produced.
- Maintaining historical data in order to make reports.
- A snapshot enables people to have access to data from a specific point in time. For example, you can generate a database snapshot at the conclusion of a certain time period (for example, a fiscal quarter) for use in later reports. After then, the snapshot may be utilized to produce period-end reports.
- Additionally, if sufficient disc space is available, you may preserve end-of-period snapshots indefinitely, allowing queries against the results of these periods for reasons such as analyzing organizational performance.
- By utilizing a mirror database that you maintain for availability purposes, you may offload reports.
- By combining database snapshots with database mirroring, you may enable reportability for the data on the mirror server. Additionally, searching the mirror database relieves the original database of resources.
- Defending Data Against Administrative Errors
- If a user makes a mistake on a source database, it can be restored to the state it was in when a database snapshot was created. The loss of data is restricted to database changes made since the snapshot was produced.
- Creating a database snapshot, for example, prior to conducting large changes, such as a bulk update or schema change, saves data. If you make a mistake, you may revert to the snapshot and restore the database. Although reverting is potentially faster than restoring from a backup, you cannot roll back later.
Defending Data From Human Error
By creating database snapshots on a regular basis, you may mitigate the impact of a large user error, such as a dropped table.
To ensure optimal security, you can create a series of database snapshots that span enough time to notice and respond to the vast majority of user failures.
For instance, depending on the capacity of your hard disc, you may maintain six to twelve rolling snapshots throughout a 24-hour period. Following that, each time a new snapshot is created, the prior one can be deleted.
You can roll back the database to the snapshot taken right before the incident occurred to recover from a user mistake. Although reverting is potentially faster than restoring from a backup, you cannot roll back later.
Alternatively, using the data included in a snapshot, you may be able to manually reconstruct a lost table or other missing data. For instance, you might bulk transfer data from the snapshot to the database and then merge it back in manually.
Creating And Maintaining A Test Database
When regularly performing a test procedure in a testing environment, it might be advantageous for the database to include identical data at the start of each cycle of testing.
An application developer or tester can produce a database snapshot of the test database prior to performing the first cycle. Following each test run, the database snapshot may be rapidly restored to its previous condition.
Here are some keywords that are commonly used in database language and their definitions.
A Database Snapshot
The transactionally consistent, read-only, static representation of a database (the source database).
The database was used to create the database snapshot. Database snapshots are relational in nature and rely on the source database.
The snapshots of a database must be kept on the same server instance as the database itself. Additionally, if a database becomes inaccessible for whatever reason, all of its database snapshots become unavailable.
A file produced by the NTFS file system requires significantly less disc space than it would otherwise. A sparse file is used to store pages that have been copied to a database snapshot.
When a sparse file is created, it takes up very little disc space. As data is written to a database snapshot, NTFS gradually allocates space on the disc to the corresponding sparse file.
In an SQL server, a snapshot is a statistical view of the database (the source database) that can only be seen by the person who made it.
A database snapshot should always be kept on the same server as the original database for security reasons.
There are several benefits to snapshotting a database occasionally, one of which is preventing human error in your data.
It is also a very useful method you can use to generate accurate reports of data from a specific database and time period.
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