About "pg_ctl promote" of PostgreSQL9.1 Today I test the new feature about "replication features" of PostgreSQL9.1, 
First I have installed the Hot-standby of PostgreSQL9.1 successfully. It is not a problem。
What I want to test is that I want to use command "pg_ctl start promote " to active  standby node 
instead of creating a trigger file 。 Yes, after I execute the command, the standby node then becomes
primary and allow write/read operations。  But the initial primary node can not switchover to the 
standby role automatically. I am not sure If PostgreSQL9.1 is able to use "pg_ctl promote" do  switchover
between primary and standby node 。Can any body explain this ?
There is no 'demote' option for pg_ctl - if the primary was cold when the standby was promoted perhaps it could be converted to a standby manually, but otherwise it will need a new base backup from the new primary.

The normal reason for switchover would be if the primary has failed so this would not be necessary.