052-189(新增70题2018)

View Exhibit.

Which two options are used to enable the connect-time failover feature? (Choose two.)

Exhibit:

A. Use only the first address.

B. Try one address, selected at random.

C. Try each address, in order, until one succeeds.

D. Try each address, randomly, until one succeeds.

E. Use each address in order until destination reached.

Answer: CD

 About Connect-time Failover
The connect-time failover enables clients to connect to another listener if the initial connection to the first 
  listener fails. The number of listener protocol addresses determines how many listeners are tried. Without 
  connect-time failover, Oracle Net attempts a connection with only one listener. The default is on.

  Tnsnames Parameter: FAILOVER 
  (failover=on) is default for ADDRESS_LISTs, DESCRIPTION_LISTs, and a set of 
  DESCRIPTIONs., therefore, you do not have to specify it explicitly.
大致意思是FAILOVER功能是默认开启的，当有多个listener，连接第一个失败时连接第二个，如果失败继续知道全部listener都被尝试过了就会返回一个错误。选项E是一直循环尝试直到成功。