LiveCache

Briefly cache LiveView assigns to prevent recalculating them during connected mounts.

For example:

• Cache a database query to avoid duplicate identical queries, resulting in a faster connected mount
• Cache a random value to determine which content to display in an A/B test

By using assign_cached/4, an assign evaluated during the disconnected mount of a LiveView is temporarily cached in ETS, for retrieval during the connected mount that immediately follows.

def mount(_params, _session, socket) do
  socket = assign_cached(socket, :users, fn ->
    Accounts.list_users()
  end)

  {:ok, socket}
end

Cached values are not stored for very long. The cache is invalidated as soon as the connected mount occurs, or after 5 seconds (configurable), whichever comes first. In the event of a cache miss, the function is evaluated again.

Live navigation to the LiveView will always result in a cache miss.

The caching of LiveComponent assigns is not currently supported.

Scoping Cached Values

For assigns that depend on external parameters, the :scope option can be used to guarantee uniqueness of the stored value.

def mount(%{"id" => id}, _session, socket) do
  socket = assign_cached(socket, :post, fn -> Blog.get_post(id) end, scope: id)
  {:ok, socket}
end

Implementation Details

The cache is rehydrated by storing a one-time key in a <meta> tag in the DOM, which is then passed as a connection param when the LiveSocket client connects. For enhanced security, the cached values can also be scoped to the current session with the LiveCache.PerSession plug.

The cache is stored locally in ETS, and is not distributed. If your production application has multiple nodes running behind a load balancer, the load balancer must be configured with "sticky sessions" so that subsequent requests from the same user are handled by the same node.

See HexDoc for complete documentation and installation instructions.

LiveView 0.18+ is supported.