log message be dropped and socket:setkeepalive error

Hello! When I use openresty and syslog-ng to log message, I had two problems . My server parameters: sock_type=tcp,flush_limit=2048,periodic_flush=10,pool_size=100.

First, drop message problem, if request rate is fast,ngx.timer pending count increase. My understanding is that the scheduled task is waiting to be executed and flush data is too slow(milliseconds), resulting the buffer_size is not zero, so msg_len + buffer_size > drop_limit.Right?

Second, socket:setkeepalive error, i get the error message: "resend log messages to the log server: connection in dubious state". I think this error send data multiple times. how to resolve it?

Thanks