What is “backlog” in TCP connections?

by

NOTE : Answers are framed without having any background in Python, but, the questions are irrelevant to language, to be answered.

What are these queued connections?

In simple words, the backlog parameter specifies the number of pending connections the queue will hold.

When multiple clients connect to the server, the server then holds the incoming requests in a queue. The clients are arranged in the queue, and the server processes their requests one by one as and when queue-member proceeds. The nature of this kind of connection is called queued connection.

Does it make any difference for client requests? (I mean is the server
that is running with socket.listen(5) different from the server that
is running with socket.listen(1) in accepting connection requests or
in receiving data?)

Yes, both cases are different. The first case would allow only 5 clients to be arranged to the queue; whereas in the case of backlog=1, only 1 connection can be hold in the queue, thereby resulting in the dropping of the further connection request!

Why is the minimum value zero? Shouldn’t it be at least 1?

I have no idea about Python, but, as per this source, in C, a backlog argument of 0 may allow the socket to accept connections, in which case the length of the listen queue may be set to an implementation-defined minimum value.

Is there a preferred value?

This question has no well-defined answer. I’d say this depends on the nature of your application, as well as the hardware configurations and software configuration too. Again, as per the source, BackLog is silently limited to between 1 and 5, inclusive(again as per C).

Is this backlog defined for TCP connections only or does it apply for UDP
and other protocols too?

NO. Please note that there’s no need to listen() or accept() for unconnected datagram sockets(UDP). This is one of the perks of using unconnected datagram sockets!

But, do keep in mind, then there are TCP based datagram socket implementations (called TCPDatagramSocket) too which have backlog parameter.

More Related Contents:

  1. What do you use when you need reliable UDP?
  2. Python socket.accept nonblocking?
  3. Sending a file over TCP sockets in Python
  4. Socket Programming Python: How to make sure entire message is received?
  5. Socket Programming Python: How to make sure entire message is received?
  6. How to close a socket left open by a killed program?
  7. When source_address of python socket.create_connection is used? [closed]
  8. Python socket not receiving without sending
  9. Interprocess communication in Python
  10. TypeError: a bytes-like object is required, not ‘str’
  11. socket.error: [Errno 10013] An attempt was made to access a socket in a way forbidden by its access permissions
  12. Why is it impossible, without attempting I/O, to detect that TCP socket was gracefully closed by peer?
  13. On localhost, how do I pick a free port number?
  14. Python Socket Flush
  15. Opening a SSL socket connection in Python
  16. Python socket connection timeout
  17. How to connect to a remote Windows machine to execute commands using python?
  18. Why am I getting the error “connection refused” in Python? (Sockets)
  19. Read timeout using either urllib2 or any other http library
  20. 104, ‘Connection reset by peer’ socket error, or When does closing a socket result in a RST rather than FIN?
  21. Discovering public IP programmatically
  22. socket.error:[errno 99] cannot assign requested address and namespace in python
  23. Can I run a Python script as a service?
  24. When does socket.recv(recv_size) return?
  25. How to use socket in Python as a context manager?
  26. How to make a simple multithreaded socket server in Python that remembers clients
  27. How do you determine if an IP address is private, in Python?
  28. Making moves w/ websockets and python / django ( / twisted? )
  29. WinError 10049: The requested address is not valid in its context
  30. Sending multiple files through a TCP socket

Leave a Comment