Snapshots

Snapshots are representations of the state of a system, data set, or environment at a specific moment in time. They are used to preserve, compare, or restore configurations without duplicating all data.

In storage systems and file systems, snapshots enable point-in-time copies by using copy-on-write or redirect-on-write techniques. They reference existing data blocks and only record changes after the capture, reducing storage usage and allowing quick restoration of files, volumes, or entire systems. Snapshots may be read-only or support reversible operations.

In databases, snapshots provide a consistent view of data as of a chosen timestamp, often implemented with multi-version concurrency control. They support long-running queries, point-in-time recovery, and can be used to create replicas or backups without blocking ongoing transactions.

In virtualization and cloud environments, a snapshot captures the state of a virtual machine, including its disk image and, in some products, memory and CPU state. This enables rollback to a previous point and can simplify cloning and backup workflows.

In software development, commits in version control systems are commonly described as snapshots of the repository at a moment in time. They preserve file contents and history, enabling branching, merging, and rollback of changes.

In photography, a snapshot denotes an informal photograph taken quickly to capture a moment, especially before digital cameras popularized casual, impulsive image capture.

Limitations include storage overhead for frequent snapshots, potential performance impacts during creation, and data consistency considerations when writes occur concurrently with snapshot operations. The precise behavior and features of snapshots vary by domain and technology.