Consistent Read
Oracle's read-consistency mechanism that reconstructs data as of a query's appropriate SCN using undo when newer changes are present.
Oracle Runtime Context
Oracle consistent read reconstructs the row versions appropriate to a query's snapshot SCN when blocks contain newer changes. Statement-level read consistency therefore lets a query preserve its logical view even while other transactions commit.
Storage Boundary
Consistent read does not require a physical historical copy of every data block. Oracle can combine the current block with undo information to reconstruct an older logical image, which makes sufficient undo retention important for long-running queries.
Related Oracle Concepts
Source
- https://docs.oracle.com/en/database/oracle/oracle-database/19/cncpt/data-concurrency-and-consistency.html