Which statement is true regarding this connect string?

Siegfried

Answer: B, C

http://www.oracle.com/technetwork/database/availability/active-data-guard-wp-12c-1896127.pdf (see 6 page)

Synchronous redo transport requires a primary database to wait for confirmation from the standby that redo has been received and written to disk (a standby redo log file) before commit success is signaled to the application. Synchronous transport combined with the deep understanding of transaction semantics by Data Guard apply services provides a guarantee of zero data loss if the primary database suddenly fails.

Although there is no physical limit to the distance between primary and standby sites, there is a practical limit to the distance that can be supported. As distance increases, the amount of time that the primary must wait to receive standby acknowledgement also increases, directly impacting application response time and throughput. There are two new synchronous transport options available in Oracle Database 12c designed to address this performance concern:

Fast Sync provides an easy way of improving performance in synchronous zero data loss configurations. Fast Sync allows a standby to acknowledge the primary database as soon as it receives redo in memory, without waiting for disk I/O to a standby redo log file. This reduces the impact of synchronous transport on primary database performance by shortening the total round-trip time between primary and standby. Fast Sync can introduce a very small exposure to data loss should simultaneous failures impact both primary and standby databases before the standby I/O completes. The time interval, however, is so brief (both failures must occur within milliseconds of each other) and the circumstances so unique that there is a very low likelihood that this would occur. Fast Sync is included with Data Guard

Far Sync enables a zero data loss failover to a remote standby database even if it is located thousands of miles away, without affecting primary database performance or materially increasing cost or complexity. Far Sync is included with Active Data Guard (see the Active Data Guard section of this paper for more details).

Asynchronous redo transport avoids any impact to primary database performance by acknowledging commit success to the application as soon as the local log-file write is complete; it never waits for the standby database to acknowledge receipt. This performance benefit comes with the potential for a small amount of data loss because can be no guarantee that at any moment in time all redo for committed transactions has been received by the standby.