DBI connect('dbname=xxx;host=yyy','username',...) failed: server closed the connection unexpectedly
This probably means the server terminated abnormally
before or while processing the request. at....
from our network statistic collector.
I spent some time trying to understand what had happened (besides yesterdays power fail). I looked at PostgreSQL server debug log (it honestly told that client just closed connection). There were no traces of dying postgres backend. I rolled back some minor configuration changes which I made yesterday... And later it downed upon me: it was just one old server which was supposed to have its network interface shut down waked after power failure... It was seen in dmesg:
arp: x.y.z.w moved from AA:AA:AA:AA:AA:AA to BB:BB:BB:BB:BB:BB on em0
arp: x.y.z.w moved from BB:BB:BB:BB:BB:BB to AA:AA:AA:AA:AA:AA on em0
Really, power cycling is neccessary sometimes to ascertain that all your services are configured properly :)