Other phases, such as logging, may require a sequence of handlers. In some phases, a list of handlers is called in order until one returns a code indicating that it handled the task. An example of this is the URI translation phase. A final significant architectural feature of Apache is the concept of a resource pool. All request-related resources, such as file handlers or memory, are allocated by a dedicated resource pool.
Modules can define their own resource pools to manage private resources.
Robust handling of resources is extremely important because Apache uses persistent processes, and resource leaks could slowly drain the system. This is a list of significant Apache modules. Modules included by default when Apache is built are in boldface. Thus, the Apache Web site has a module registry for developers to submit modules, and for users to download modules. This registry is at modules.apache.org .