Real-Time Apply standby waiting for logs to ship from primary creating gaps

 

I am trying to learn Active Data Guard configuration. The Oracle document says, If the real-time apply feature is enabled, apply services can apply redo data as it is received, without waiting for the current standby redo log file to be archived. The remote file server (RFS) process writes the redo data to standby redo log files on the standby database, apply services can recover redo from standby redo log files as they are being filled. [Referece: http://docs.oracle.com/cd/E11882_01/server.112/e25608/log_apply.htm#autoId2].

Even i enabled real-time apply, i am experiencing heavy gaps. This results cumulative addition gaps every hour and standby gets lagged behind production. Checking the alert log, i always see waiting for media recovery for sequence# (in transit) even the real-time apply is enabled.