Syntax options:

    SNAPSHOT IS IMMEDIATE | SNAPSHOT IS DEFERRED

    Specifies when read/write transactions write database changes to
    the snapshot file used by read-only transactions.

    The ENABLED IMMEDIATE option is the default and causes read/write
    transactions to write copies of rows they modify to the snapshot
    file, regardless of whether or not a read-only transaction is
    active. Although ENABLED IMMEDIATE is the default, if you set
    snapshots ENABLED DEFERRED, you must specify both ENABLED and
    IMMEDIATE options to return the database to the default setting.

    The ENABLED DEFERRED option lets read/write transactions
    avoid writing copies of rows they modify to the snapshot file
    (unless a read-only transaction is already active). Deferring
    snapshot writing in this manner improves the performance for
    the read/write transaction. However, read-only transactions that
    start after an active read/write transaction starts must wait for
    all active read/write users to complete their transactions.