Hot Code Loading & Upgrades

Erlang's hot code loading is a standout feature! It lets you update a running application's code without stopping it. Imagine changing parts of a website's backend while it's actively serving users, without any downtime!

This capability is crucial for systems that need to run continuously, like telecommunications switches or large-scale distributed services. It ensures maximum uptime and service availability.

The Erlang Virtual Machine (BEAM) manages code modules in a unique way. For each module, it can keep two versions loaded in memory: an 'old' version and a 'new' version.

• When a process starts, it runs the 'new' version of the code.
• If you reload a module, new calls to its functions will use the very latest 'new' version.
• However, existing processes continue to execute the code they were loaded with until they make a call to a function in the *reloaded* module or are explicitly told to change.