Kernel Parameters

When dealing with large numbers of concurrent connections there are a handful of kernel parameters that you might need to adjust. Generally these should only affect sites with a very large concurrent load. These parameters are not specific to Gunicorn, they would apply to any sort of network server you may be running.

These commands are for Linux. Your particular OS may have slightly different parameters.

How can I increase the maximum number of file descriptors?

One of the first settings that usually needs to be bumped is the maximum number of open file descriptors for a given process. For the confused out there, remember that Unices treat sockets as files.

$ sudo ulimit -n 2048

How can I increase the maximum socket backlog?

Listening sockets have an associated queue of incoming connections that are waiting to be accepted. If you happen to have a stampede of clients that fill up this queue new connections will eventually start getting dropped.

$ sudo sysctl -w net.core.somaxconn="2048"

How can I disable the use of sendfile()

Disabling the use sendfile() can be done by using the --no-sendfile setting or by setting the environment variable SENDFILE to 0.