Snapshot

A snapshot represents a dataset's state at a defined point in its evolution. It can be a materialized copy or a logical view of stored versions. Its meaning depends on the system's consistency rules and on the scope being captured.

Copying over time is not automatically one state

Suppose an export reads orders at 09:00 and refunds at 09:05 while both tables are changing. The files may combine states that never existed together. An export job's start time alone does not make that collection a consistent snapshot.

PostgreSQL documents how transaction isolation determines the snapshots seen by queries. A suitable database mechanism can provide a consistent read scope; copying multiple independent systems requires additional coordination or an explicit account of their different cutoffs.

State is different from history

If an order changed from pending to paid before the snapshot, a current-state snapshot may retain only paid. It cannot reconstruct every earlier transition. Change records or historical versions are needed for that purpose.

A file containing a day's events describes an interval of activity, which is different from a snapshot of system state. Record whether the data represents state or events, along with filters, capture scope, and version. A snapshot can support backup or repeatable analysis, but recovery also depends on retention, accessibility, and the ability to restore it.

Reference: PostgreSQL: Transaction isolation.