To change the maximum allowed backlog by your system (*nix machines only), first you need to find the variable for this limit:
sudo sysctl -a | grep somaxconn
On ubuntu boxes, it returns net.core.somaxconn (you need to look for the 'somaxconn' variable, the full name will vary across different systems).
Update this to a large number as follows:
sudo sysctl -w net.core.somaxconn=1024
This will work straight away. no restart required.
(PHP 4 >= 4.1.0, PHP 5)
socket_listen — Listens for a connection on a socket
$backlog= 0 ] )
socket_listen() is applicable only to sockets of
A valid socket resource created with socket_create().
A maximum of
backlogincoming connections will be queued for processing. If a connection request arrives with the queue full the client may receive an error with an indication of ECONNREFUSED, or, if the underlying protocol supports retransmission, the request may be ignored so that retries may succeed.
The maximum number passed to the
backlogparameter highly depends on the underlying platform. On Linux, it is silently truncated to
SOMAXCONN. On win32, if passed
SOMAXCONN, the underlying service provider responsible for the socket will set the backlog to a maximum reasonable value. There is no standard provision to find out the actual backlog value on this platform.
socket_listen() cannot be used for UDP communications as discussed below.
In addition, the example below discusses UDP connections, which only exist if the application manages them through a state table (the OS does not create a UDP connection upon receiving a datagram). Having a function named socket_connect() that determines the remote IP and port only confuses the matter by giving the indication of some sort of connection handshake between two hosts. Rather, socket_connect() only specifies the remote IP and port used by subsequent socket_send() calls. You can achieve the same effect by skipping socket_connect() altogether and specifying the remote IP and port in socket_sendto() calls.
If you find yourself writing a connection-based protocol on top of UDP, consider using TCP. If your application requires streaming data of some sort, use TCP to manage connections and control messages, and UDP to handle the streaming data (H.323 is an example of a suite of TCP and UDP protocols working in conjunction).