[Dovecot] Dovecot pgsqlauthentication database reconnection/failover problem

[Frank Wang]

Hi,
    Our mail system uses dovecot-1.0-1.2.rc15.el5 in Centos-5.1 as our imap 
server. It connects to a pgsql database in another server as authentication 
backend. It works fine except occasionally fails to reconnect to the database 
after temporary network block, and dovecot has to be restarted to work again 
in such case. Since I can't find any specific setting in dovecot.conf to 
handle this reconnection problem, I opt to build a failover pgsql backend. 
Google led me to  
http://www.dovecot.org/list/dovecot/2008-January/027899.html.  I followed the 
thread to modify my dovecot-sql.conf containing "connect = host=pgsql1 
host=pgsql2 dbname=xxxx user=xxxx"
   If both databases are available, dovecot will choose pgsql2 as the default 
one, and user login works flawlessly. But when I block all traffic to host 
pgsql2, dovecot will repeatedly try pgsql2 and neglect available host pgsql1. 
   I don't find relevent information in the dovecot wiki either. Can anyone 
here shed a light on me?
    Thanks in advance!

Regards, 
Frank Wang