[HACKERS] [bug fix] PG10: libpq doesn't connect to alternative hosts whensome errors occur

Hello,

I found a problem with libpq connection failover.  When libpq cannot connect to earlier hosts in the host list, it
doesn'ttry to connect to other hosts.  For example, when you specify a wrong port that some non-postgres program is
using,or some non-postgres program is using PG's port unexpectedly, you get an error like this:
 

$ psql -h localhost -p 23
psql: received invalid response to SSL negotiation: 
$ psql -h localhost -p 23 -d "sslmode=disable"
psql: expected authentication request from server, but received 

Likewise, when the first host has already reached max_connections, libpq doesn't attempt the connection aginst later
hosts.

The attached patch fixes this.  I'll add this item in the PostgreSQL 10 Open Items.


Regards
Takayuki Tsunakawa


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