From 437a3350ff44ce0fc964f89989c261958c93454a Mon Sep 17 00:00:00 2001
From: hq1 <hq@mtod.org>
Date: Tue, 12 Mar 2024 07:58:12 +0100
Subject: [PATCH] Replace caching engine (#3878)

* Dependencies: swap Cachex for ConCache

* Implement Cache adapter wrapping ConCache

* Implement cache stats tracker, for metrics

* Use Cache.Adapter in Plausible.Cache

Marking the test as not slow anymore

* Use Cache Adapter when tracking sessions

* Use Cache Adapter for UA parsing

* Rename child identifiers - cachex is obsolete now

* Test stats tracking

* Update grafana metrics

* Put all caches under common child specification

* Try less

* Shorten the function delegation path
---
 lib/plausible/application.ex                 |  27 ++---
 lib/plausible/cache.ex                       |  65 +++++------
 lib/plausible/cache/adapter.ex               | 107 +++++++++++++++++++
 lib/plausible/cache/stats.ex                 |  74 +++++++++++++
 lib/plausible/ingestion/event.ex             |   8 +-
 lib/plausible/session/cache_store.ex         |  13 +--
 lib/plausible/shield/country_rule_cache.ex   |   2 +-
 lib/plausible/shield/ip_rule_cache.ex        |   2 +-
 lib/plausible/site/cache.ex                  |   2 +-
 lib/plausible/telemetry/plausible_metrics.ex |  38 +++----
 mix.exs                                      |   4 +-
 mix.lock                                     |   2 +-
 test/plausible/cache/stats_test.exs          |  50 +++++++++
 test/plausible/cache_test.exs                |  28 ++++-
 test/plausible/site/cache_test.exs           |   1 -
 15 files changed, 323 insertions(+), 100 deletions(-)
 create mode 100644 lib/plausible/cache/adapter.ex
 create mode 100644 lib/plausible/cache/stats.ex
 create mode 100644 test/plausible/cache/stats_test.exs

diff --git a/lib/plausible/application.ex b/lib/plausible/application.ex
index 8f2b62215..bdc0aa9bc 100644
--- a/lib/plausible/application.ex
+++ b/lib/plausible/application.ex
@@ -10,6 +10,7 @@ defmodule Plausible.Application do
     on_full_build(do: Plausible.License.ensure_valid_license())
 
     children = [
+      Plausible.Cache.Stats,
       Plausible.Repo,
       Plausible.ClickhouseRepo,
       Plausible.IngestRepo,
@@ -23,13 +24,15 @@ defmodule Plausible.Application do
       Supervisor.child_spec(Plausible.Event.WriteBuffer, id: Plausible.Event.WriteBuffer),
       Supervisor.child_spec(Plausible.Session.WriteBuffer, id: Plausible.Session.WriteBuffer),
       ReferrerBlocklist,
-      Supervisor.child_spec({Cachex, name: :user_agents, limit: 10_000, stats: true},
-        id: :cachex_user_agents
+      Plausible.Cache.Adapter.child_spec(:user_agents, :cache_user_agents,
+        ttl_check_interval: :timer.seconds(5),
+        global_ttl: :timer.minutes(60)
       ),
-      Supervisor.child_spec({Cachex, name: :sessions, limit: nil, stats: true},
-        id: :cachex_sessions
+      Plausible.Cache.Adapter.child_spec(:sessions, :cache_sessions,
+        ttl_check_interval: :timer.seconds(1),
+        global_ttl: :timer.minutes(30)
       ),
-      {Plausible.Site.Cache, []},
+      {Plausible.Site.Cache, ttl_check_interval: false},
       {Plausible.Cache.Warmer,
        [
          child_name: Plausible.Site.Cache.All,
@@ -44,7 +47,7 @@ defmodule Plausible.Application do
          interval: :timer.seconds(30),
          warmer_fn: :refresh_updated_recently
        ]},
-      {Plausible.Shield.IPRuleCache, []},
+      {Plausible.Shield.IPRuleCache, ttl_check_interval: false},
       {Plausible.Cache.Warmer,
        [
          child_name: Plausible.Shield.IPRuleCache.All,
@@ -59,7 +62,7 @@ defmodule Plausible.Application do
          interval: :timer.seconds(35),
          warmer_fn: :refresh_updated_recently
        ]},
-      {Plausible.Shield.CountryRuleCache, []},
+      {Plausible.Shield.CountryRuleCache, ttl_check_interval: false},
       {Plausible.Cache.Warmer,
        [
          child_name: Plausible.Shield.CountryRuleCache.All,
@@ -168,16 +171,6 @@ defmodule Plausible.Application do
     )
   end
 
-  def report_cache_stats() do
-    case Cachex.stats(:user_agents) do
-      {:ok, stats} ->
-        Logger.info("User agent cache stats: #{inspect(stats)}")
-
-      e ->
-        IO.puts("Unable to show cache stats: #{inspect(e)}")
-    end
-  end
-
   defp setup_opentelemetry() do
     OpentelemetryPhoenix.setup()
     OpentelemetryEcto.setup([:plausible, :repo])
diff --git a/lib/plausible/cache.ex b/lib/plausible/cache.ex
index 5f27bda82..17ec2d2cf 100644
--- a/lib/plausible/cache.ex
+++ b/lib/plausible/cache.ex
@@ -8,10 +8,10 @@ defmodule Plausible.Cache do
       # - Optionally override `unwrap_cache_keys/1`
       # - Populate the cache with `Plausible.Cache.Warmer`
 
-  Serves as a thin wrapper around Cachex, but the underlying
+  Serves as a wrapper around `Plausible.Cache.Adapter`, where the underlying
   implementation can be transparently swapped.
 
-  Even though the Cachex process is started, cache access is disabled
+  Even though normally the relevant Adapter processes are started, cache access is disabled
   during tests via the `:plausible, #{__MODULE__}, enabled: bool()` application env key.
   This can be overridden on case by case basis, using the child specs options.
 
@@ -61,29 +61,33 @@ defmodule Plausible.Cache do
       @behaviour Plausible.Cache
       @modes [:all, :updated_recently]
 
+      alias Plausible.Cache.Adapter
+
       @spec get(any(), Keyword.t()) :: any() | nil
-      def get(key, opts \\ []) do
+      def get(key, opts \\ []) when is_list(opts) do
         cache_name = Keyword.get(opts, :cache_name, name())
         force? = Keyword.get(opts, :force?, false)
 
         if Plausible.Cache.enabled?() or force? do
-          case Cachex.get(cache_name, key) do
-            {:ok, nil} ->
-              nil
-
-            {:ok, item} ->
-              item
-
-            {:error, e} ->
-              Logger.error("Error retrieving key from '#{inspect(cache_name)}': #{inspect(e)}")
-
-              nil
-          end
+          Adapter.get(cache_name, key)
         else
           get_from_source(key)
         end
       end
 
+      @spec get_or_store(any(), (-> any()), Keyword.t()) :: any() | nil
+      def get_or_store(key, fallback_fn, opts \\ [])
+          when is_function(fallback_fn, 0) and is_list(opts) do
+        cache_name = Keyword.get(opts, :cache_name, name())
+        force? = Keyword.get(opts, :force?, false)
+
+        if Plausible.Cache.enabled?() or force? do
+          Adapter.get(cache_name, key, fallback_fn)
+        else
+          get_from_source(key) || fallback_fn.()
+        end
+      end
+
       def unwrap_cache_keys(items), do: items
       defoverridable unwrap_cache_keys: 1
 
@@ -117,10 +121,10 @@ defmodule Plausible.Cache do
       def merge_items(new_items, opts) do
         new_items = unwrap_cache_keys(new_items)
         cache_name = Keyword.get(opts, :cache_name, name())
-        true = Cachex.put_many!(cache_name, new_items)
+        :ok = Adapter.put_many(cache_name, new_items)
 
         if Keyword.get(opts, :delete_stale_items?, true) do
-          {:ok, old_keys} = Cachex.keys(cache_name)
+          old_keys = Adapter.keys(cache_name)
 
           new = MapSet.new(Enum.into(new_items, [], fn {k, _} -> k end))
           old = MapSet.new(old_keys)
@@ -128,7 +132,7 @@ defmodule Plausible.Cache do
           old
           |> MapSet.difference(new)
           |> Enum.each(fn k ->
-            Cachex.del(cache_name, k)
+            Adapter.delete(cache_name, k)
           end)
         end
 
@@ -139,11 +143,7 @@ defmodule Plausible.Cache do
       def child_spec(opts) do
         cache_name = Keyword.get(opts, :cache_name, name())
         child_id = Keyword.get(opts, :child_id, child_id())
-
-        Supervisor.child_spec(
-          {Cachex, name: cache_name, limit: nil, stats: true},
-          id: child_id
-        )
+        Adapter.child_spec(cache_name, child_id, opts)
       end
 
       @doc """
@@ -154,7 +154,7 @@ defmodule Plausible.Cache do
       @spec ready?(atom()) :: boolean
       def ready?(cache_name \\ name()) do
         case size(cache_name) do
-          n when n > 0 ->
+          n when is_integer(n) and n > 0 ->
             true
 
           0 ->
@@ -165,21 +165,8 @@ defmodule Plausible.Cache do
         end
       end
 
-      @spec size() :: non_neg_integer()
-      def size(cache_name \\ name()) do
-        case Cachex.size(cache_name) do
-          {:ok, size} -> size
-          _ -> 0
-        end
-      end
-
-      @spec hit_rate() :: number()
-      def hit_rate(cache_name \\ name()) do
-        case Cachex.stats(cache_name) do
-          {:ok, stats} -> Map.get(stats, :hit_rate, 0)
-          _ -> 0
-        end
-      end
+      defdelegate size(cache_name \\ name()), to: Plausible.Cache.Adapter
+      defdelegate hit_rate(cache_name \\ name()), to: Plausible.Cache.Stats
 
       @spec telemetry_event_refresh(atom(), atom()) :: list(atom())
       def telemetry_event_refresh(cache_name \\ name(), mode) when mode in @modes do
diff --git a/lib/plausible/cache/adapter.ex b/lib/plausible/cache/adapter.ex
new file mode 100644
index 000000000..a4a4a8aeb
--- /dev/null
+++ b/lib/plausible/cache/adapter.ex
@@ -0,0 +1,107 @@
+defmodule Plausible.Cache.Adapter do
+  @moduledoc """
+  Interface for the underlying cache implementation.
+  Currently: ConCache
+
+  Using the Adapter module directly, the user must ensure that the relevant
+  processes are available to use, which is normally done via the child specification.
+  """
+
+  require Logger
+
+  @spec child_spec(atom(), atom(), Keyword.t()) :: Supervisor.child_spec()
+  def child_spec(name, child_id, opts \\ [])
+      when is_atom(name) and is_atom(child_id) and is_list(opts) do
+    cache_name = Keyword.get(opts, :cache_name, name)
+    child_id = Keyword.get(opts, :child_id, child_id)
+    ttl_check_interval = Keyword.get(opts, :ttl_check_interval, false)
+
+    opts =
+      opts
+      |> Keyword.put(:name, cache_name)
+      |> Keyword.put(:ttl_check_interval, ttl_check_interval)
+
+    Supervisor.child_spec(
+      {ConCache, opts},
+      id: child_id
+    )
+  end
+
+  @spec size(atom()) :: non_neg_integer() | nil
+  def size(cache_name) do
+    ConCache.size(cache_name)
+  catch
+    :exit, _ -> nil
+  end
+
+  @spec get(atom(), any()) :: any()
+  def get(cache_name, key) do
+    cache_name
+    |> ConCache.get(key)
+    |> Plausible.Cache.Stats.track(cache_name)
+  catch
+    :exit, _ ->
+      Logger.error("Error retrieving key from '#{inspect(cache_name)}'")
+      nil
+  end
+
+  @spec get(atom(), any(), (-> any())) :: any()
+  def get(cache_name, key, fallback_fn) do
+    cache_name
+    |> ConCache.get_or_store(key, fn ->
+      {:from_fallback, fallback_fn.()}
+    end)
+    |> Plausible.Cache.Stats.track(cache_name)
+  catch
+    :exit, _ ->
+      Logger.error("Error retrieving key from '#{inspect(cache_name)}'")
+      nil
+  end
+
+  @spec put(atom(), any(), any()) :: any()
+  def put(cache_name, key, value) do
+    :ok = ConCache.put(cache_name, key, value)
+    value
+  catch
+    :exit, _ ->
+      Logger.error("Error putting a key to '#{cache_name}'")
+      nil
+  end
+
+  @spec put_many(atom(), [any()]) :: :ok
+  def put_many(cache_name, items) when is_list(items) do
+    true = :ets.insert(ConCache.ets(cache_name), items)
+    :ok
+  catch
+    :exit, _ ->
+      Logger.error("Error putting keys to '#{cache_name}'")
+      :ok
+  end
+
+  @spec delete(atom(), any()) :: :ok
+  def delete(cache_name, key) do
+    ConCache.dirty_delete(cache_name, key)
+  catch
+    :exit, _ ->
+      Logger.error("Error deleting a key in '#{cache_name}'")
+      :ok
+  end
+
+  @spec keys(atom()) :: Enumerable.t()
+  def keys(cache_name) do
+    ets = ConCache.ets(cache_name)
+
+    Stream.resource(
+      fn -> :ets.first(ets) end,
+      fn
+        :"$end_of_table" -> {:halt, nil}
+        prev_key -> {[prev_key], :ets.next(ets, prev_key)}
+      end,
+      fn _ -> :ok end
+    )
+  catch
+    :exit, _ ->
+      Logger.error("Error retrieving key from '#{inspect(cache_name)}'")
+      []
+  end
+end
diff --git a/lib/plausible/cache/stats.ex b/lib/plausible/cache/stats.ex
new file mode 100644
index 000000000..b1b240eb4
--- /dev/null
+++ b/lib/plausible/cache/stats.ex
@@ -0,0 +1,74 @@
+defmodule Plausible.Cache.Stats do
+  @moduledoc """
+  Keeps track of hit/miss ratio for various caches.
+  """
+
+  use GenServer
+
+  def start_link(opts) do
+    GenServer.start_link(__MODULE__, opts)
+  end
+
+  def init(opts) do
+    table = Keyword.get(opts, :table, __MODULE__)
+
+    ^table =
+      :ets.new(table, [
+        :public,
+        :named_table,
+        :ordered_set,
+        read_concurrency: true,
+        write_concurrency: true
+      ])
+
+    {:ok, table}
+  end
+
+  def gather(cache_name, table \\ __MODULE__) do
+    {:ok,
+     %{
+       hit_rate: hit_rate(cache_name, table),
+       count: size(cache_name) || 0
+     }}
+  end
+
+  defdelegate size(cache_name), to: Plausible.Cache.Adapter
+
+  def track(item, cache_name, table \\ __MODULE__)
+
+  def track({:from_fallback, item}, cache_name, table) do
+    bump(cache_name, :miss, 1, table)
+    item
+  end
+
+  def track(nil, cache_name, table) do
+    bump(cache_name, :miss, 1, table)
+    nil
+  end
+
+  def track(item, cache_name, table) do
+    bump(cache_name, :hit, 1, table)
+    item
+  end
+
+  def bump(cache_name, type, increment, table \\ __MODULE__) do
+    :ets.update_counter(
+      table,
+      {cache_name, type},
+      increment,
+      {{cache_name, type}, 0}
+    )
+  end
+
+  def hit_rate(cache_name, table \\ __MODULE__) do
+    hit = :ets.lookup_element(table, {cache_name, :hit}, 2, 0)
+    miss = :ets.lookup_element(table, {cache_name, :miss}, 2, 0)
+    hit_miss = hit + miss
+
+    if hit_miss == 0 do
+      0.0
+    else
+      hit / hit_miss * 100
+    end
+  end
+end
diff --git a/lib/plausible/ingestion/event.ex b/lib/plausible/ingestion/event.ex
index f11c435ac..3211055c5 100644
--- a/lib/plausible/ingestion/event.ex
+++ b/lib/plausible/ingestion/event.ex
@@ -388,11 +388,9 @@ defmodule Plausible.Ingestion.Event do
   end
 
   defp parse_user_agent(%Request{user_agent: user_agent}) when is_binary(user_agent) do
-    case Cachex.fetch(:user_agents, user_agent, &UAInspector.parse/1) do
-      {:ok, user_agent} -> user_agent
-      {:commit, user_agent} -> user_agent
-      _ -> nil
-    end
+    Plausible.Cache.Adapter.get(:user_agents, user_agent, fn ->
+      UAInspector.parse(user_agent)
+    end)
   end
 
   defp parse_user_agent(request), do: request
diff --git a/lib/plausible/session/cache_store.ex b/lib/plausible/session/cache_store.ex
index 6c29407d5..830453528 100644
--- a/lib/plausible/session/cache_store.ex
+++ b/lib/plausible/session/cache_store.ex
@@ -19,27 +19,22 @@ defmodule Plausible.Session.CacheStore do
   defp find_session(_domain, nil), do: nil
 
   defp find_session(event, user_id) do
-    from_cache = Cachex.get(:sessions, {event.site_id, user_id})
+    from_cache = Plausible.Cache.Adapter.get(:sessions, {event.site_id, user_id})
 
     case from_cache do
-      {:ok, nil} ->
+      nil ->
         nil
 
-      {:ok, session} ->
+      session ->
         if Timex.diff(event.timestamp, session.timestamp, :minutes) <= 30 do
           session
         end
-
-      {:error, e} ->
-        Sentry.capture_message("Cachex error", extra: %{error: e})
-        nil
     end
   end
 
   defp persist_session(session) do
     key = {session.site_id, session.user_id}
-    Cachex.put(:sessions, key, session, ttl: :timer.minutes(30))
-    session
+    Plausible.Cache.Adapter.put(:sessions, key, session)
   end
 
   defp update_session(session, event) do
diff --git a/lib/plausible/shield/country_rule_cache.ex b/lib/plausible/shield/country_rule_cache.ex
index ec42232b7..453e0226e 100644
--- a/lib/plausible/shield/country_rule_cache.ex
+++ b/lib/plausible/shield/country_rule_cache.ex
@@ -19,7 +19,7 @@ defmodule Plausible.Shield.CountryRuleCache do
   def name(), do: @cache_name
 
   @impl true
-  def child_id(), do: :cachex_country_blocklist
+  def child_id(), do: :cache_country_blocklist
 
   @impl true
   def count_all() do
diff --git a/lib/plausible/shield/ip_rule_cache.ex b/lib/plausible/shield/ip_rule_cache.ex
index 9b941ba19..7644a9477 100644
--- a/lib/plausible/shield/ip_rule_cache.ex
+++ b/lib/plausible/shield/ip_rule_cache.ex
@@ -19,7 +19,7 @@ defmodule Plausible.Shield.IPRuleCache do
   def name(), do: @cache_name
 
   @impl true
-  def child_id(), do: :cachex_ip_blocklist
+  def child_id(), do: :cache_ip_blocklist
 
   @impl true
   def count_all() do
diff --git a/lib/plausible/site/cache.ex b/lib/plausible/site/cache.ex
index 2c9e850a5..67944cca1 100644
--- a/lib/plausible/site/cache.ex
+++ b/lib/plausible/site/cache.ex
@@ -37,7 +37,7 @@ defmodule Plausible.Site.Cache do
   def name(), do: @cache_name
 
   @impl true
-  def child_id(), do: :cachex_sites
+  def child_id(), do: :cache_sites
 
   @impl true
   def count_all() do
diff --git a/lib/plausible/telemetry/plausible_metrics.ex b/lib/plausible/telemetry/plausible_metrics.ex
index c5cb11265..80e78d25b 100644
--- a/lib/plausible/telemetry/plausible_metrics.ex
+++ b/lib/plausible/telemetry/plausible_metrics.ex
@@ -88,29 +88,23 @@ defmodule Plausible.PromEx.Plugins.PlausibleMetrics do
   end
 
   @doc """
-  Add telemetry events for Cachex user agents and sessions
+  Fire telemetry events for various caches
   """
   def execute_cache_metrics do
-    {:ok, user_agents_stats} = Cachex.stats(:user_agents)
-    {:ok, sessions_stats} = Cachex.stats(:sessions)
+    {:ok, user_agents_stats} = Plausible.Cache.Stats.gather(:user_agents)
+    {:ok, sessions_stats} = Plausible.Cache.Stats.gather(:sessions)
 
-    user_agents_hit_rate = Map.get(user_agents_stats, :hit_rate, 0.0)
-    sessions_hit_rate = Map.get(sessions_stats, :hit_rate, 0.0)
-
-    {:ok, user_agents_count} = Cachex.size(:user_agents)
-    {:ok, sessions_count} = Cachex.size(:sessions)
-
-    :telemetry.execute([:prom_ex, :plugin, :cachex, :user_agents], %{
-      count: user_agents_count,
-      hit_rate: user_agents_hit_rate
+    :telemetry.execute([:prom_ex, :plugin, :cache, :user_agents], %{
+      count: user_agents_stats.count,
+      hit_rate: user_agents_stats.hit_rate
     })
 
-    :telemetry.execute([:prom_ex, :plugin, :cachex, :sessions], %{
-      count: sessions_count,
-      hit_rate: sessions_hit_rate
+    :telemetry.execute([:prom_ex, :plugin, :cache, :sessions], %{
+      count: sessions_stats.count,
+      hit_rate: sessions_stats.hit_rate
     })
 
-    :telemetry.execute([:prom_ex, :plugin, :cachex, :sites], %{
+    :telemetry.execute([:prom_ex, :plugin, :cache, :sites], %{
       count: Site.Cache.size(),
       hit_rate: Site.Cache.hit_rate()
     })
@@ -144,32 +138,32 @@ defmodule Plausible.PromEx.Plugins.PlausibleMetrics do
       [
         last_value(
           metric_prefix ++ [:cache, :sessions, :size],
-          event_name: [:prom_ex, :plugin, :cachex, :sessions],
+          event_name: [:prom_ex, :plugin, :cache, :sessions],
           measurement: :count
         ),
         last_value(
           metric_prefix ++ [:cache, :user_agents, :size],
-          event_name: [:prom_ex, :plugin, :cachex, :user_agents],
+          event_name: [:prom_ex, :plugin, :cache, :user_agents],
           measurement: :count
         ),
         last_value(
           metric_prefix ++ [:cache, :user_agents, :hit_ratio],
-          event_name: [:prom_ex, :plugin, :cachex, :user_agents],
+          event_name: [:prom_ex, :plugin, :cache, :user_agents],
           measurement: :hit_rate
         ),
         last_value(
           metric_prefix ++ [:cache, :sessions, :hit_ratio],
-          event_name: [:prom_ex, :plugin, :cachex, :sessions],
+          event_name: [:prom_ex, :plugin, :cache, :sessions],
           measurement: :hit_rate
         ),
         last_value(
           metric_prefix ++ [:cache, :sites, :size],
-          event_name: [:prom_ex, :plugin, :cachex, :sites],
+          event_name: [:prom_ex, :plugin, :cache, :sites],
           measurement: :count
         ),
         last_value(
           metric_prefix ++ [:cache, :sites, :hit_ratio],
-          event_name: [:prom_ex, :plugin, :cachex, :sites],
+          event_name: [:prom_ex, :plugin, :cache, :sites],
           measurement: :hit_rate
         )
       ]
diff --git a/mix.exs b/mix.exs
index 95c76fdf5..f434ad6ca 100644
--- a/mix.exs
+++ b/mix.exs
@@ -67,7 +67,6 @@ defmodule Plausible.MixProject do
       {:bamboo_mua, "~> 0.1.4"},
       {:bcrypt_elixir, "~> 3.0"},
       {:bypass, "~> 2.1", only: [:dev, :test, :small_test]},
-      {:cachex, "~> 3.4"},
       {:ecto_ch, "~> 0.3"},
       {:cloak, "~> 1.1"},
       {:cloak_ecto, "~> 1.2"},
@@ -140,7 +139,8 @@ defmodule Plausible.MixProject do
       {:ex_aws, "~> 2.5"},
       {:ex_aws_s3, "~> 2.5"},
       {:sweet_xml, "~> 0.7.4"},
-      {:testcontainers, "~> 1.6", only: [:test, :small_test]}
+      {:testcontainers, "~> 1.6", only: [:test, :small_test]},
+      {:con_cache, "~> 1.0"}
     ]
   end
 
diff --git a/mix.lock b/mix.lock
index a985822b3..2669598ce 100644
--- a/mix.lock
+++ b/mix.lock
@@ -8,7 +8,6 @@
   "bcrypt_elixir": {:hex, :bcrypt_elixir, "3.1.0", "0b110a9a6c619b19a7f73fa3004aa11d6e719a67e672d1633dc36b6b2290a0f7", [:make, :mix], [{:comeonin, "~> 5.3", [hex: :comeonin, repo: "hexpm", optional: false]}, {:elixir_make, "~> 0.6", [hex: :elixir_make, repo: "hexpm", optional: false]}], "hexpm", "2ad2acb5a8bc049e8d5aa267802631912bb80d5f4110a178ae7999e69dca1bf7"},
   "bunt": {:hex, :bunt, "1.0.0", "081c2c665f086849e6d57900292b3a161727ab40431219529f13c4ddcf3e7a44", [:mix], [], "hexpm", "dc5f86aa08a5f6fa6b8096f0735c4e76d54ae5c9fa2c143e5a1fc7c1cd9bb6b5"},
   "bypass": {:hex, :bypass, "2.1.0", "909782781bf8e20ee86a9cabde36b259d44af8b9f38756173e8f5e2e1fabb9b1", [:mix], [{:plug, "~> 1.7", [hex: :plug, repo: "hexpm", optional: false]}, {:plug_cowboy, "~> 2.0", [hex: :plug_cowboy, repo: "hexpm", optional: false]}, {:ranch, "~> 1.3", [hex: :ranch, repo: "hexpm", optional: false]}], "hexpm", "d9b5df8fa5b7a6efa08384e9bbecfe4ce61c77d28a4282f79e02f1ef78d96b80"},
-  "cachex": {:hex, :cachex, "3.6.0", "14a1bfbeee060dd9bec25a5b6f4e4691e3670ebda28c8ba2884b12fe30b36bf8", [:mix], [{:eternal, "~> 1.2", [hex: :eternal, repo: "hexpm", optional: false]}, {:jumper, "~> 1.0", [hex: :jumper, repo: "hexpm", optional: false]}, {:sleeplocks, "~> 1.1", [hex: :sleeplocks, repo: "hexpm", optional: false]}, {:unsafe, "~> 1.0", [hex: :unsafe, repo: "hexpm", optional: false]}], "hexpm", "ebf24e373883bc8e0c8d894a63bbe102ae13d918f790121f5cfe6e485cc8e2e2"},
   "castore": {:hex, :castore, "1.0.5", "9eeebb394cc9a0f3ae56b813459f990abb0a3dedee1be6b27fdb50301930502f", [:mix], [], "hexpm", "8d7c597c3e4a64c395980882d4bca3cebb8d74197c590dc272cfd3b6a6310578"},
   "certifi": {:hex, :certifi, "2.12.0", "2d1cca2ec95f59643862af91f001478c9863c2ac9cb6e2f89780bfd8de987329", [:rebar3], [], "hexpm", "ee68d85df22e554040cdb4be100f33873ac6051387baf6a8f6ce82272340ff1c"},
   "ch": {:hex, :ch, "0.2.4", "d510fbb5542d009f7c5b00bb1ecab73307b6066d9fb9b220600257d462cba67f", [:mix], [{:db_connection, "~> 2.0", [hex: :db_connection, repo: "hexpm", optional: false]}, {:decimal, "~> 2.0", [hex: :decimal, repo: "hexpm", optional: false]}, {:ecto, "~> 3.5", [hex: :ecto, repo: "hexpm", optional: true]}, {:jason, "~> 1.0", [hex: :jason, repo: "hexpm", optional: false]}, {:mint, "~> 1.0", [hex: :mint, repo: "hexpm", optional: false]}], "hexpm", "8f065d15aaf912ae8da56c9ca5298fb2d1a09108d006de589bcf8c2b39a7e2bb"},
@@ -19,6 +18,7 @@
   "combination": {:hex, :combination, "0.0.3", "746aedca63d833293ec6e835aa1f34974868829b1486b1e1cb0685f0b2ae1f41", [:mix], [], "hexpm", "72b099f463df42ef7dc6371d250c7070b57b6c5902853f69deb894f79eda18ca"},
   "combine": {:hex, :combine, "0.10.0", "eff8224eeb56498a2af13011d142c5e7997a80c8f5b97c499f84c841032e429f", [:mix], [], "hexpm", "1b1dbc1790073076580d0d1d64e42eae2366583e7aecd455d1215b0d16f2451b"},
   "comeonin": {:hex, :comeonin, "5.4.0", "246a56ca3f41d404380fc6465650ddaa532c7f98be4bda1b4656b3a37cc13abe", [:mix], [], "hexpm", "796393a9e50d01999d56b7b8420ab0481a7538d0caf80919da493b4a6e51faf1"},
+  "con_cache": {:hex, :con_cache, "1.0.0", "6405e2bd5d5005334af72939432783562a8c35a196c2e63108fe10bb97b366e6", [:mix], [], "hexpm", "4d1f5cb1a67f3c1a468243dc98d10ac83af7f3e33b7e7c15999dc2c9bc0a551e"},
   "cors_plug": {:hex, :cors_plug, "3.0.3", "7c3ac52b39624bc616db2e937c282f3f623f25f8d550068b6710e58d04a0e330", [:mix], [{:plug, "~> 1.13", [hex: :plug, repo: "hexpm", optional: false]}], "hexpm", "3f2d759e8c272ed3835fab2ef11b46bddab8c1ab9528167bd463b6452edf830d"},
   "cowboy": {:hex, :cowboy, "2.10.0", "ff9ffeff91dae4ae270dd975642997afe2a1179d94b1887863e43f681a203e26", [:make, :rebar3], [{:cowlib, "2.12.1", [hex: :cowlib, repo: "hexpm", optional: false]}, {:ranch, "1.8.0", [hex: :ranch, repo: "hexpm", optional: false]}], "hexpm", "3afdccb7183cc6f143cb14d3cf51fa00e53db9ec80cdcd525482f5e99bc41d6b"},
   "cowboy_telemetry": {:hex, :cowboy_telemetry, "0.4.0", "f239f68b588efa7707abce16a84d0d2acf3a0f50571f8bb7f56a15865aae820c", [:rebar3], [{:cowboy, "~> 2.7", [hex: :cowboy, repo: "hexpm", optional: false]}, {:telemetry, "~> 1.0", [hex: :telemetry, repo: "hexpm", optional: false]}], "hexpm", "7d98bac1ee4565d31b62d59f8823dfd8356a169e7fcbb83831b8a5397404c9de"},
diff --git a/test/plausible/cache/stats_test.exs b/test/plausible/cache/stats_test.exs
new file mode 100644
index 000000000..557ab6f48
--- /dev/null
+++ b/test/plausible/cache/stats_test.exs
@@ -0,0 +1,50 @@
+defmodule Plausible.Cache.StatsTest do
+  use Plausible.DataCase, async: true
+
+  alias Plausible.Cache.Stats
+
+  test "when tracking is not initialized, stats are 0" do
+    assert {:ok, %{hit_rate: +0.0, count: 0}} = Stats.gather(:foo)
+  end
+
+  test "when cache is started, stats are 0", %{test: test} do
+    {:ok, _} = Stats.start_link(name: test, table: test)
+    assert {:ok, %{hit_rate: +0.0, count: 0}} = Stats.gather(test, test)
+  end
+
+  test "tracking changes hit ratio", %{test: test} do
+    {:ok, _} = Stats.start_link(name: test, table: test)
+
+    Stats.track(nil, test, test)
+    assert {:ok, %{hit_rate: +0.0, count: 0}} = Stats.gather(test, test)
+
+    Stats.track(:not_nil, test, test)
+    assert {:ok, %{hit_rate: 50.0, count: 0}} = Stats.gather(test, test)
+
+    Stats.track(:not_nil, test, test)
+    Stats.track(:not_nil, test, test)
+    assert {:ok, %{hit_rate: 75.0, count: 0}} = Stats.gather(test, test)
+
+    Stats.track(nil, test, test)
+    Stats.track(nil, test, test)
+    assert {:ok, %{hit_rate: 50.0, count: 0}} = Stats.gather(test, test)
+  end
+
+  test "bump by custom number", %{test: test} do
+    {:ok, _} = Stats.start_link(name: test, table: test)
+    Stats.bump(test, :miss, 10, test)
+    assert {:ok, %{hit_rate: +0.0, count: 0}} = Stats.gather(test, test)
+    Stats.bump(test, :hit, 90, test)
+    assert {:ok, %{hit_rate: 90.0, count: 0}} = Stats.gather(test, test)
+  end
+
+  test "count comes from cache adapter", %{test: test} do
+    {:ok, _} = Stats.start_link(name: test, table: test)
+    %{start: {m, f, a}} = Plausible.Cache.Adapter.child_spec(test, test)
+    {:ok, _} = apply(m, f, a)
+
+    Plausible.Cache.Adapter.put(test, :key, :value)
+    assert Stats.size(test) == 1
+    assert {:ok, %{hit_rate: +0.0, count: 1}} = Stats.gather(test, test)
+  end
+end
diff --git a/test/plausible/cache_test.exs b/test/plausible/cache_test.exs
index 0e66c25f6..2190f09c8 100644
--- a/test/plausible/cache_test.exs
+++ b/test/plausible/cache_test.exs
@@ -50,7 +50,7 @@ defmodule Plausible.CacheTest do
           assert ExampleCache.get("key", force?: true, cache_name: NonExistingCache) == nil
         end)
 
-      assert log =~ "Error retrieving key from 'NonExistingCache': :no_cache"
+      assert log =~ "Error retrieving key from 'NonExistingCache'"
     end
 
     test "cache is not ready when it doesn't exist", %{test: test} do
@@ -58,6 +58,32 @@ defmodule Plausible.CacheTest do
     end
   end
 
+  describe "stats tracking" do
+    test "get affects hit rate", %{test: test} do
+      {:ok, _} = start_test_cache(test)
+      :ok = ExampleCache.merge_items([{"item1", :item1}], cache_name: test)
+      assert ExampleCache.get("item1", cache_name: test, force?: true)
+      assert {:ok, %{hit_rate: 100.0}} = Plausible.Cache.Stats.gather(test)
+      refute ExampleCache.get("item2", cache_name: test, force?: true)
+      assert {:ok, %{hit_rate: 50.0}} = Plausible.Cache.Stats.gather(test)
+    end
+
+    test "get_or_store affects hit rate", %{test: test} do
+      {:ok, _} = start_test_cache(test)
+
+      :ok = ExampleCache.merge_items([{"item1", :item1}], cache_name: test)
+      assert ExampleCache.get("item1", cache_name: test, force?: true)
+
+      assert "value" ==
+               ExampleCache.get_or_store("item2", fn -> "value" end,
+                 cache_name: test,
+                 force?: true
+               )
+
+      assert {:ok, %{hit_rate: 50.0}} = Plausible.Cache.Stats.gather(test)
+    end
+  end
+
   describe "merging cache items" do
     test "merging adds new items", %{test: test} do
       {:ok, _} = start_test_cache(test)
diff --git a/test/plausible/site/cache_test.exs b/test/plausible/site/cache_test.exs
index de2cb6ca3..7c5a889f7 100644
--- a/test/plausible/site/cache_test.exs
+++ b/test/plausible/site/cache_test.exs
@@ -323,7 +323,6 @@ defmodule Plausible.Site.CacheTest do
     @items1 for i <- 1..200_000, do: {i, nil, :batch1}
     @items2 for _ <- 1..200_000, do: {Enum.random(1..400_000), nil, :batch2}
     @max_seconds 2
-    @tag :slow
     test "merging large sets is expected to be under #{@max_seconds} seconds", %{test: test} do
       {:ok, _} = start_test_cache(test)