Ask the experts to check the increasing Recv-Q in netstat. Why?

Ask the experts to check the increasing Recv-Q in netstat. Why? -- Linux general technology-Linux technology and application information. For details, refer to the following section. The client uses persistent connections to the server. the client sends a request to the server. After processing, the server sends the data to the client. after the system runs for a period of time, the server cannot receive the data sent from the client, but the client log prompts that the message has been successfully sent out (write does not return an error ). check with netstat on the client and find that the Recv-Q contains data. As the number of sent packets increases, the Recv-Q keeps increasing.
First time
Tcp 0 254 221.5.148.222: 43993 222.42.38.25: 9814 ESTABLISHED
Second
Tcp 0 339 221.5.148.222: 43993 222.42.38.25: 9814 ESTABLISHED
Similarly, restart the client program and restore it to normal until the fault is reproduced.

I wonder if anyone has encountered such a problem?