This modules allows you to gather and aggregate various statistics easily. It is used by Prosody to offer the module:measure() API. If you are developing a module, you should use that. If you want to expose statistics from core code in Prosody, use core.statsmanager.
local registry = require "util.statistics".new();
A registry is a collection of statistics, each statistics identified by a string key. No particular format is enforced for the keys.