ETS keeps its data entirely separate from all processes so when you access an ETS you copy the between the table and the process. HOWEVER you do not copy the whole table each time only the elements you actually access. This does mean you should not store all the data in one element but in multiple elements and you the key to select which element.

Actually there is no way to avoid copying data if you are sharing data between processes, keeping it in an ETS table or storing it somewhere “outside” the erlang/elixir system. It’s a fact of life. Just make sure you can access it in small chunks.

Depending on how often your shared data does change maybe look at this one: GitHub - discord/fastglobal: Fast no copy globals for Elixir & Erlang. · GitHub

It becomes less of a surprise if you think through the implications of doing that. Erlang does garbage collection on the process level, which is very simple in multiple regards: process memory is small, and processes are interruptable so a small pause to do a quick GC is acceptable. This keeps GC simple. Now, think of the case when you would get data by reference out of a process (an Agent is just a process) - suddenly the GC has to keep track of pointers globally in the VM and simplicity gets tossed out of the window.

(the actual details are, of course, a bit more complicated than I just said. This seems to be a decent quick overview with pointers to further reading. Erlang will ask you to open the hood and look at how the engine works a bit sooner than other systems, but the pay-off is good performing stable code and the investment isn’t that high (compared to, say, learning the Java Memory Model). Well worth it.)