Hi.
I found the cause of the error that tcp_keepalive doesn't work.
The cause is a specification of linux kernel.
In the specification of linux kernel, tcp_keepalive doesn't work
if the network outage occurs before receiving ACK for send() system-call.
This behavior of tcp_keepalive is reported even by LKML.
Linux-Kernel Archive: Re: 2.6.12.5 bug? per-socket TCP keepalive settings
http://www.ussg.iu.edu/hypermail/linux/kernel/0508.2/0757.html
I'm confused whether tcp_keepalive problem should be solved
at the DB level.
regards;