Specifies that read/write transactions not write copies of
    records they modify to the snapshot file unless a read-only
    transaction is active. Read-only transactions that attempt to
    start after an active read/write transaction begins must wait for
    all active read/write users to complete their transactions.

    If you use the SNAPSHOT IS ENABLED clause to enable snapshots
    on a multifile database, writing to all snapshot files for all
    storage areas is enabled.