oracle 9.2 is a new feature, logical standby dataase,It is very
useful, but it seems it is too comples to use and needs developing.

but the physical standby database very well now.
it has.
a. auotmatic logfile gap detection, and standby databae can request archive logfile not recieved.

b. recover operation can be place backgroup

c. If primary database crashed and can not open, it can archive current redo logfile;