Snapshot versioning describes the type of versioning access that the database server uses for tables: table-level snapshot versioning, or row-level snapshot versioning. Row-level versioning allows concurrent writer access and row-level locking for RLV-enabled tables.
Table-level versioning is the default, and provides versioning based on the entire table.
Row-level versioning provides versioning at the row level against a fixed table version. Versioning occurs at transaction start time. Once the snapshot version has been defined for a started transaction, you cannot change it until the transaction is complete.