Performance

This chapter describes the performance characteristics of Cowboy and offers suggestions to get the most performance out of your application.

One process per connection

The first version of Cowboy featured a single process per connection, whereas the current version of Cowboy features one process per connection plus one process per request. This has a negative impact on performance, but is necessary in order to provide a common interface for both HTTP/1.1 and HTTP/2 (as well as future HTTP versions).

It is still possible to use a single process per connection, and avoid the creation of additional processes for each request, by implementing a stream handler to process the requests. This can be done for all requests, or just for a single endpoint depending on the application's needs.

Stream handlers provide an asynchronous interface and must not block, so the implementation will be very different from normal Cowboy handlers, but the performance gains are important enough to justify it in some cases.