A repaint is a change in appearance of a DOM (Document Object Model) element, while a reflow is a change/recalculation of the position of the elements in the DOM. You should avoid triggering these two operations as they are resource-expensive, especially in terms of CPU usage.

Each time a web server receives an HTTP request, it saves this information in a log, generally translating the user’s IP address into a domain name. This conversion (DNS lookup) is one of the Apache HTTP server’s bottlenecks and should therefore be disabled.