Why performance of sending durable messages to qpid queue is really bad?

With Proton c++ client, it seems sending an undurable message to a qpid queue
takes 1-3ms, while sending a durable message takes static 1000ms. Is it by
design? Why does it take so much time?

My code:
pn_message_set_durable(message, true);

for(i=0;i<10;i++){
gettimeofday(닖 NULL);
printf("sending %d ", i);
pn_messenger_put(messenger, message);
messageTracker = pn_messenger_outgoing_tracker(messenger);
pn_messenger_send(messenger, -1);

pn_status_t trackerStatus = pn_messenger_status(messenger,
messageTracker);
if(trackerStatus != PN_STATUS_ACCEPTED) printf("send Azure failed! %d\n",
trackerStatus);
else pn_messenger_settle(messenger,messageTracker,0);

gettimeofday(穷 NULL);
seconds = end.tv_sec - start.tv_sec;
useconds = end.tv_usec - start.tv_usec;
mtime = ((seconds) * 1000 + useconds/1000.0) + 0.5;
printf(" after send one Elapsed time: %ld milliseconds\n", mtime);