dets

If you want a disk-based version of :ets, then dets is your solution, at least if your state fits into a file of less than 2 GB. Moving the state to disk could free up some memory, but it will come with a significant performance decrease because all operations are now disk operations.

# Define a path for the file. If the file doesn't exist, dets will create it.
# We have to convert the string to a charlist here, because that's what :dets expects.
dets_file_path = String.to_charlist("./state.dets")

# Open a new file
{:ok, _pid} = :dets.open_file(:state, file: dets_file_path)

# Write records to the file
:dets.insert(:state, {:messi, %{age: 37, goals: 837}})
:dets.insert(:state, {:ronaldo, %{age: 39, goals: 900}})

# Look up a value
:dets.lookup(:state, :messi) |> IO.inspect(label: 1)

# Update a value by overwriting it
:dets.insert(:state, {:messi, %{age: 37, goals: 838}})
:dets.lookup(:state, :messi) |> IO.inspect(label: 2)

# Delete a record
:dets.delete(:state, :messi)
:dets.lookup(:state, :messi) |> IO.inspect(label: 3)

# Flush the changes to disk. A file is auto-flushed every 3 minutes by default.
# You can change this interval with the `auto_save: 1_000` option in `:dets.open_file/2`
:dets.sync(:state)

# Close the file. Don't forget this, otherwise your file isn't closed properly
# and needs to be repaired the next time you open it, which might take a while.
#
# If you open the file from a process and the process terminates, this will be
# called automatically.
:dets.close(:state)

1: [messi: %{age: 37, goals: 837}]
2: [messi: %{age: 37, goals: 838}]
3: []