Unreliable Unix Domain DGRAM socket?

[Qiao Yang]

Hi all,

Does anyone know what possible scenarios may cause the Unix Domain DGRAM
socket to lose packet? We know, in theory, it is unreliable, but in reality,
I rarely see packet loss happens to this type of socket. Unfortunately, I
believe it happened a few times in the last couple of months in a FreeBSD
5.3 box and I wasn't able to track down what the cause was.

One related question. Considering the following setup, client (socket_A)
send a packet to server (socket_B). If the sending buffer of socket_A is ok
but the receiving buffer of socket_B is full, will sendto() return error?

Thanks for your insights.
--Qiao