Working metrics for all forms of interactions and updated .env.example

.env.example

@@ -27,3 +27,14 @@ S3_VIRTUAL_HOST=false
 
 # Email (Brevo)
 BREVO_API_KEY=your-brevo-api-key
+
+# ClickHouse (analytics / metrics)
+# single connection URL (overrides all individual vars below)
+CLICKHOUSE_URL=http://default:password@localhost:8123/mixer_metrics
+# individual vars (used when CLICKHOUSE_URL is not set)
+CLICKHOUSE_HOST=localhost
+CLICKHOUSE_PORT=8123
+CLICKHOUSE_DATABASE=mixer_metrics
+CLICKHOUSE_USERNAME=default
+CLICKHOUSE_PASSWORD=
+CLICKHOUSE_SCHEME=http

config/config.exs

@@ -94,7 +94,7 @@ config :spark,
   ]
 
 config :mixer,
-  ecto_repos: [Mixer.Repo],
+  ecto_repos: [Mixer.Repo, Mixer.ClickhouseRepo],
   generators: [timestamp_type: :utc_datetime],
   ash_domains: [Mixer.Accounts, Mixer.Posts],
   ash_authentication: [return_error_on_invalid_magic_link_token?: true]
@@ -158,6 +158,11 @@ config :logger, :default_formatter,
 # Use Jason for JSON parsing in Phoenix
 config :phoenix, :json_library, Jason
 
+# ClickHouse repo — migrations live in priv/clickhouse/migrations
+config :mixer, Mixer.ClickhouseRepo,
+  priv: "priv/clickhouse",
+  migration_source: "ch_schema_migrations"
+
 # Import environment specific config. This must remain at the bottom
 # of this file so it overrides the configuration defined above.
 import_config "#{config_env()}.exs"

config/dev.exs

@@ -106,3 +106,12 @@ config :ex_aws, :s3,
 config :waffle,
   bucket: "mixer-bucket",
   asset_host: "http://localhost:9000"
+
+# ClickHouse (default local install)
+config :mixer, Mixer.ClickhouseRepo,
+  scheme: "http",
+  hostname: "localhost",
+  port: 8123,
+  database: "mixer_metrics",
+  username: "default",
+  password: ""

config/runtime.exs

@@ -22,6 +22,11 @@ end
 
 config :mixer, MixerWeb.Endpoint, http: [port: String.to_integer(System.get_env("PORT", "4000"))]
 
+# ClickHouse is available in all environments via env vars when set
+if clickhouse_url = System.get_env("CLICKHOUSE_URL") do
+  config :mixer, Mixer.ClickhouseRepo, url: clickhouse_url
+end
+
 if config_env() == :prod do
   database_url =
     System.get_env("DATABASE_URL") ||
@@ -40,6 +45,19 @@ if config_env() == :prod do
     # pool_count: 4,
     socket_options: maybe_ipv6
 
+  # ClickHouse — configure via CLICKHOUSE_URL or individual vars
+  unless System.get_env("CLICKHOUSE_URL") do
+    config :mixer, Mixer.ClickhouseRepo,
+      scheme: System.get_env("CLICKHOUSE_SCHEME", "http"),
+      hostname:
+        System.get_env("CLICKHOUSE_HOST") ||
+          raise("Missing environment variable `CLICKHOUSE_HOST`!"),
+      port: String.to_integer(System.get_env("CLICKHOUSE_PORT", "8123")),
+      database: System.get_env("CLICKHOUSE_DATABASE", "mixer_metrics"),
+      username: System.get_env("CLICKHOUSE_USERNAME", "default"),
+      password: System.get_env("CLICKHOUSE_PASSWORD", "")
+  end
+
   # The secret key base is used to sign/encrypt cookies and other secrets.
   # A default value is used in config/dev.exs and config/test.exs but you
   # want to use a different value for prod and you most likely don't want

config/test.exs

@@ -42,3 +42,12 @@ config :phoenix_live_view,
 # Sort query params output of verified routes for robust url comparisons
 config :phoenix,
   sort_verified_routes_query_params: true
+
+# ClickHouse — point at a dedicated test database
+config :mixer, Mixer.ClickhouseRepo,
+  scheme: "http",
+  hostname: "localhost",
+  port: 8123,
+  database: "mixer_metrics_test",
+  username: "default",
+  password: ""

lib/mixer/application.ex

@@ -10,6 +10,10 @@ defmodule Mixer.Application do
     children = [
       MixerWeb.Telemetry,
       Mixer.Repo,
+      # ClickHouse repo for analytics — started before the metrics buffer
+      Mixer.ClickhouseRepo,
+      # In-memory event buffer that batches writes to ClickHouse
+      Mixer.Metrics.Buffer,
       {DNSCluster, query: Application.get_env(:mixer, :dns_cluster_query) || :ignore},
       {Phoenix.PubSub, name: Mixer.PubSub},
       # Start a worker by calling: Mixer.Worker.start_link(arg)

lib/mixer/clickhouse_repo.ex

@@ -0,0 +1,13 @@
+defmodule Mixer.ClickhouseRepo do
+  @moduledoc """
+  Ecto repository for ClickHouse, backed by the `ecto_ch` / `Ch` adapter.
+
+  Used exclusively for analytics writes (via `Mixer.Metrics.Buffer`) and
+  read queries (via `Mixer.Metrics`). It is **not** an Ash repo and must
+  never be used for transactional application data.
+  """
+
+  use Ecto.Repo,
+    otp_app: :mixer,
+    adapter: Ecto.Adapters.ClickHouse
+end

lib/mixer/metrics.ex

@@ -0,0 +1,291 @@
+defmodule Mixer.Metrics do
+  @moduledoc """
+  Public API for tracking and querying post (tweet) metrics via ClickHouse.
+
+  ## Tracking events
+
+  Tracking calls are non-blocking — events are handed off to the in-memory
+  `Mixer.Metrics.Buffer` GenServer and written to ClickHouse in batches.
+
+      # Record a tweet view (anonymous)
+      Mixer.Metrics.track_view(tweet_id)
+
+      # Record a view with a logged-in user and their IP
+      Mixer.Metrics.track_view(tweet_id, user_id: user.id, ip_address: conn.remote_ip)
+
+  ## Querying metrics
+
+  Query functions execute synchronous ClickHouse SQL and return plain maps.
+
+      {:ok, summary} = Mixer.Metrics.get_summary(tweet_id)
+      # => %{views: 42, likes: 7, unlikes: 1, comments: 3, shares: 0}
+
+      {:ok, rows} = Mixer.Metrics.get_top_posts(10)
+      # => [%{tweet_id: "...", views: 99}, ...]
+  """
+
+  require Logger
+
+  alias Mixer.ClickhouseRepo
+  alias Mixer.Metrics.Buffer
+
+  # ---------------------------------------------------------------------------
+  # Event types
+  # ---------------------------------------------------------------------------
+
+  @type event_type ::
+          :view | :post | :comment | :like | :unlike | :share | :delete_post | :delete_comment
+
+  @type track_opt ::
+          {:user_id, binary() | nil}
+          | {:ip_address, binary() | :inet.ip_address() | nil}
+
+  # ---------------------------------------------------------------------------
+  # Tracking helpers
+  # ---------------------------------------------------------------------------
+
+  @doc """
+  Track a tweet view event.
+
+  ## Options
+
+    * `:user_id` — UUID of the viewing user (nil for anonymous)
+    * `:ip_address` — originating IP; accepts a string or an `:inet` tuple
+  """
+  @spec track_view(binary(), [track_opt()]) :: :ok
+  def track_view(tweet_id, opts \\ []), do: enqueue("view", tweet_id, opts)
+
+  @doc "Track a tweet like event."
+  @spec track_like(binary(), [track_opt()]) :: :ok
+  def track_like(tweet_id, opts \\ []), do: enqueue("like", tweet_id, opts)
+
+  @doc "Track a tweet unlike event."
+  @spec track_unlike(binary(), [track_opt()]) :: :ok
+  def track_unlike(tweet_id, opts \\ []), do: enqueue("unlike", tweet_id, opts)
+
+  @doc "Track a comment (reply) event on a tweet."
+  @spec track_comment(binary(), [track_opt()]) :: :ok
+  def track_comment(tweet_id, opts \\ []), do: enqueue("comment", tweet_id, opts)
+
+  @doc "Track a tweet share / repost event."
+  @spec track_share(binary(), [track_opt()]) :: :ok
+  def track_share(tweet_id, opts \\ []), do: enqueue("share", tweet_id, opts)
+
+  @doc """
+  Track a new top-level tweet being published.
+
+  The event is recorded against the new tweet's own ID.
+  """
+  @spec track_post(binary(), [track_opt()]) :: :ok
+  def track_post(tweet_id, opts \\ []), do: enqueue("post", tweet_id, opts)
+
+  @doc """
+  Track a top-level tweet being deleted.
+
+  The event is recorded against the deleted tweet's ID.
+  Note: cascade-deleted comments are not individually tracked — only the
+  explicit user-initiated destroy action emits this event.
+  """
+  @spec track_delete_post(binary(), [track_opt()]) :: :ok
+  def track_delete_post(tweet_id, opts \\ []), do: enqueue("delete_post", tweet_id, opts)
+
+  @doc """
+  Track a comment (reply) being deleted.
+
+  The event is recorded against the *parent* tweet's ID so that
+  `get_summary/1` can reflect net comment activity on a tweet.
+  """
+  @spec track_delete_comment(binary(), [track_opt()]) :: :ok
+  def track_delete_comment(tweet_id, opts \\ []), do: enqueue("delete_comment", tweet_id, opts)
+
+  # ---------------------------------------------------------------------------
+  # Query helpers
+  # ---------------------------------------------------------------------------
+
+  @doc """
+  Return a summary of all event counts for a single tweet.
+
+  Returns `{:ok, map}` on success or `{:error, reason}` on failure.
+
+  ## Example
+
+      {:ok, %{views: 12, likes: 3, unlikes: 0, comments: 5, shares: 1}} =
+        Mixer.Metrics.get_summary(tweet_id)
+  """
+  @spec get_summary(binary()) :: {:ok, map()} | {:error, term()}
+  def get_summary(tweet_id) do
+    sql = """
+    SELECT
+      countIf(event_type = 'view')    AS views,
+      countIf(event_type = 'like')    AS likes,
+      countIf(event_type = 'unlike')  AS unlikes,
+      countIf(event_type = 'comment') AS comments,
+      countIf(event_type = 'share')   AS shares
+    FROM post_events
+    WHERE tweet_id = {tweet_id:String}
+    """
+
+    case ClickhouseRepo.query(sql, %{"tweet_id" => tweet_id}) do
+      {:ok, result} ->
+        {:ok, row_to_summary(result)}
+
+      {:error, reason} ->
+        Logger.error("[Mixer.Metrics] get_summary failed for #{tweet_id}: #{inspect(reason)}")
+        {:error, reason}
+    end
+  end
+
+  @doc """
+  Return view counts bucketed by UTC hour for the past `hours` hours.
+
+  Useful for rendering a sparkline on a tweet detail page.
+
+  ## Example
+
+      {:ok, rows} = Mixer.Metrics.get_hourly_views(tweet_id, 24)
+      # => [%{hour: ~N[2026-04-07 00:00:00], views: 5}, ...]
+  """
+  @spec get_hourly_views(binary(), pos_integer()) :: {:ok, [map()]} | {:error, term()}
+  def get_hourly_views(tweet_id, hours \\ 24) when is_integer(hours) and hours > 0 do
+    sql = """
+    SELECT
+      toStartOfHour(occurred_at) AS hour,
+      count()                    AS views
+    FROM post_events
+    WHERE
+      tweet_id   = {tweet_id:String}
+      AND event_type = 'view'
+      AND occurred_at >= now() - toIntervalHour({hours:UInt32})
+    GROUP BY hour
+    ORDER BY hour ASC
+    """
+
+    case ClickhouseRepo.query(sql, %{"tweet_id" => tweet_id, "hours" => hours}) do
+      {:ok, %{rows: rows}} ->
+        {:ok, Enum.map(rows, fn [hour, views] -> %{hour: hour, views: views} end)}
+
+      {:error, reason} ->
+        Logger.error("[Mixer.Metrics] get_hourly_views failed: #{inspect(reason)}")
+        {:error, reason}
+    end
+  end
+
+  @doc """
+  Return the top `limit` tweets ordered by total view count across all time.
+
+  ## Example
+
+      {:ok, rows} = Mixer.Metrics.get_top_posts(10)
+      # => [%{tweet_id: "...", views: 99}, %{tweet_id: "...", views: 72}, ...]
+  """
+  @spec get_top_posts(pos_integer()) :: {:ok, [map()]} | {:error, term()}
+  def get_top_posts(limit \\ 10) when is_integer(limit) and limit > 0 do
+    sql = """
+    SELECT
+      tweet_id,
+      countIf(event_type = 'view') AS views
+    FROM post_events
+    GROUP BY tweet_id
+    ORDER BY views DESC
+    LIMIT {limit:UInt32}
+    """
+
+    case ClickhouseRepo.query(sql, %{"limit" => limit}) do
+      {:ok, %{rows: rows}} ->
+        {:ok, Enum.map(rows, fn [tweet_id, views] -> %{tweet_id: tweet_id, views: views} end)}
+
+      {:error, reason} ->
+        Logger.error("[Mixer.Metrics] get_top_posts failed: #{inspect(reason)}")
+        {:error, reason}
+    end
+  end
+
+  @doc """
+  Return per-event-type counts for a list of tweet IDs in a single query.
+
+  Handy for batch-enriching a feed with metrics without N+1 queries.
+
+  ## Example
+
+      {:ok, map} = Mixer.Metrics.get_bulk_summaries(tweet_ids)
+      # => %{"<uuid>" => %{views: 5, likes: 2, ...}, ...}
+  """
+  @spec get_bulk_summaries([binary()]) :: {:ok, %{binary() => map()}} | {:error, term()}
+  def get_bulk_summaries([]), do: {:ok, %{}}
+
+  def get_bulk_summaries(tweet_ids) when is_list(tweet_ids) do
+    # ecto_ch supports passing arrays as query parameters
+    sql = """
+    SELECT
+      tweet_id,
+      countIf(event_type = 'view')    AS views,
+      countIf(event_type = 'like')    AS likes,
+      countIf(event_type = 'unlike')  AS unlikes,
+      countIf(event_type = 'comment') AS comments,
+      countIf(event_type = 'share')   AS shares
+    FROM post_events
+    WHERE tweet_id IN {tweet_ids:Array(String)}
+    GROUP BY tweet_id
+    """
+
+    case ClickhouseRepo.query(sql, %{"tweet_ids" => tweet_ids}) do
+      {:ok, %{rows: rows}} ->
+        summaries =
+          Map.new(rows, fn [tweet_id, views, likes, unlikes, comments, shares] ->
+            {tweet_id,
+             %{
+               views: views,
+               likes: likes,
+               unlikes: unlikes,
+               comments: comments,
+               shares: shares
+             }}
+          end)
+
+        {:ok, summaries}
+
+      {:error, reason} ->
+        Logger.error("[Mixer.Metrics] get_bulk_summaries failed: #{inspect(reason)}")
+        {:error, reason}
+    end
+  end
+
+  # ---------------------------------------------------------------------------
+  # Private helpers
+  # ---------------------------------------------------------------------------
+
+  defp enqueue(event_type, tweet_id, opts) do
+    event = %{
+      event_type: event_type,
+      tweet_id: tweet_id,
+      user_id: Keyword.get(opts, :user_id),
+      occurred_at: DateTime.utc_now() |> DateTime.truncate(:second),
+      ip_address: opts |> Keyword.get(:ip_address) |> format_ip()
+    }
+
+    Buffer.track(event)
+  end
+
+  defp format_ip(nil), do: nil
+  defp format_ip(ip) when is_binary(ip), do: ip
+
+  defp format_ip({a, b, c, d}), do: "#{a}.#{b}.#{c}.#{d}"
+
+  defp format_ip({a, b, c, d, e, f, g, h}) do
+    [a, b, c, d, e, f, g, h]
+    |> Enum.map_join(":", &Integer.to_string(&1, 16))
+  end
+
+  defp row_to_summary(%{rows: [[views, likes, unlikes, comments, shares] | _]}) do
+    %{
+      views: views,
+      likes: likes,
+      unlikes: unlikes,
+      comments: comments,
+      shares: shares
+    }
+  end
+
+  # ClickHouse returns no rows when the tweet has zero events — default to 0
+  defp row_to_summary(_), do: %{views: 0, likes: 0, unlikes: 0, comments: 0, shares: 0}
+end

lib/mixer/metrics/buffer.ex

@@ -0,0 +1,151 @@
+defmodule Mixer.Metrics.Buffer do
+  @moduledoc """
+  GenServer that accumulates post metric events in memory and flushes them
+  to ClickHouse in batches.
+
+  Two conditions trigger a flush:
+
+  1. **Timer** — every `@flush_interval` milliseconds (default 10 s).
+  2. **Threshold** — whenever the in-memory buffer reaches `@max_buffer_size`
+     rows (default 500).
+
+  If ClickHouse is unavailable the error is logged and the buffered events
+  are discarded rather than retried indefinitely, preventing unbounded memory
+  growth. For production deployments that require durability, consider adding
+  a persistent queue in front of this buffer.
+  """
+
+  use GenServer
+
+  require Logger
+
+  alias Mixer.Metrics.PostEvent
+
+  @flush_interval :timer.seconds(10)
+  @max_buffer_size 500
+
+  # ---------------------------------------------------------------------------
+  # Public API
+  # ---------------------------------------------------------------------------
+
+  @doc """
+  Start the buffer process and link it to the calling process.
+
+  Accepts an optional keyword list of overrides:
+
+    * `:flush_interval` — milliseconds between scheduled flushes
+    * `:max_buffer_size` — row count that triggers an immediate flush
+  """
+  @spec start_link(keyword()) :: GenServer.on_start()
+  def start_link(opts \\ []) do
+    GenServer.start_link(__MODULE__, opts, name: __MODULE__)
+  end
+
+  @doc """
+  Enqueue a single analytics event map for buffered insertion into ClickHouse.
+
+  The map must contain at minimum the fields required by `Mixer.Metrics.PostEvent`:
+  `:event_type`, `:tweet_id`, `:occurred_at`. Other fields are optional.
+
+  This call is asynchronous (cast) and returns `:ok` immediately.
+  """
+  @spec track(map()) :: :ok
+  def track(event) when is_map(event) do
+    GenServer.cast(__MODULE__, {:track, event})
+  end
+
+  @doc """
+  Force an immediate flush of all buffered events to ClickHouse, regardless
+  of the timer or threshold. Returns `:ok` after the flush completes.
+
+  Primarily useful in tests.
+  """
+  @spec flush() :: :ok
+  def flush do
+    GenServer.call(__MODULE__, :flush)
+  end
+
+  # ---------------------------------------------------------------------------
+  # GenServer callbacks
+  # ---------------------------------------------------------------------------
+
+  @impl GenServer
+  def init(opts) do
+    flush_interval = Keyword.get(opts, :flush_interval, @flush_interval)
+    max_buffer_size = Keyword.get(opts, :max_buffer_size, @max_buffer_size)
+
+    schedule_flush(flush_interval)
+
+    state = %{
+      events: [],
+      count: 0,
+      flush_interval: flush_interval,
+      max_buffer_size: max_buffer_size
+    }
+
+    {:ok, state}
+  end
+
+  @impl GenServer
+  def handle_cast({:track, event}, state) do
+    new_count = state.count + 1
+    new_events = [event | state.events]
+
+    if new_count >= state.max_buffer_size do
+      do_flush(new_events)
+      {:noreply, %{state | events: [], count: 0}}
+    else
+      {:noreply, %{state | events: new_events, count: new_count}}
+    end
+  end
+
+  @impl GenServer
+  def handle_call(:flush, _from, state) do
+    do_flush(state.events)
+    {:reply, :ok, %{state | events: [], count: 0}}
+  end
+
+  @impl GenServer
+  def handle_info(:flush, state) do
+    do_flush(state.events)
+    schedule_flush(state.flush_interval)
+    {:noreply, %{state | events: [], count: 0}}
+  end
+
+  @impl GenServer
+  def terminate(_reason, state) do
+    # Best-effort flush on shutdown so we don't lose buffered events during
+    # graceful stops (e.g., deploys).
+    do_flush(state.events)
+    :ok
+  end
+
+  # ---------------------------------------------------------------------------
+  # Private helpers
+  # ---------------------------------------------------------------------------
+
+  defp do_flush([]), do: :ok
+
+  defp do_flush(events) do
+    rows = Enum.reverse(events)
+    count = length(rows)
+
+    try do
+      # ClickHouse async inserts acknowledge writes immediately and always
+      # return num_rows: 0 — the data is queued for background commitment.
+      # We use our own row count for the log so it is always accurate.
+      Mixer.ClickhouseRepo.insert_all(PostEvent, rows)
+      Logger.debug("[Mixer.Metrics.Buffer] Flushed #{count} event(s) to ClickHouse")
+    rescue
+      error ->
+        Logger.error(
+          "[Mixer.Metrics.Buffer] Failed to flush #{count} event(s) to ClickHouse: " <>
+            Exception.message(error)
+        )
+    end
+  end
+
+  defp schedule_flush(interval) do
+    Process.send_after(self(), :flush, interval)
+  end
+end

lib/mixer/metrics/post_event.ex

@@ -0,0 +1,47 @@
+defmodule Mixer.Metrics.PostEvent do
+  @moduledoc """
+  Ecto schema that maps to the `post_events` table in ClickHouse.
+
+  Each row represents a single analytics event tied to a tweet (post).
+  The table uses a MergeTree engine ordered by `(occurred_at, event_type,
+  tweet_id)` for efficient time-range scans and per-tweet aggregations.
+
+  ## Event types
+
+  | event_type         | `tweet_id` refers to  | Description                                     |
+  |--------------------|-----------------------|-------------------------------------------------|
+  | `"view"`           | the viewed tweet      | Tweet detail page was loaded                    |
+  | `"post"`           | the new tweet         | A new top-level tweet was published             |
+  | `"comment"`        | the parent tweet      | A reply was posted; count against the parent    |
+  | `"like"`           | the liked tweet       | A user liked a tweet                            |
+  | `"unlike"`         | the unliked tweet     | A user removed their like                       |
+  | `"share"`          | the shared tweet      | A user shared / reposted a tweet                |
+  | `"delete_post"`    | the deleted tweet     | A top-level tweet was deleted by its author     |
+  | `"delete_comment"` | the parent tweet      | A reply was deleted; count against the parent   |
+  """
+
+  use Ecto.Schema
+
+  @primary_key false
+
+  schema "post_events" do
+    # Must be Ch-typed so ecto_ch emits LowCardinality(String) in the RowBinary
+    # header, matching the ClickHouse table DDL exactly.
+    field :event_type, Ch, type: "LowCardinality(String)"
+
+    # The tweet that the event relates to
+    field :tweet_id, Ecto.UUID
+
+    # The acting user; may be nil for anonymous views.
+    # Must be Ch-typed so ecto_ch emits Nullable(UUID) in the RowBinary header,
+    # matching the ClickHouse table DDL exactly.
+    field :user_id, Ch, type: "Nullable(UUID)"
+
+    # Wall-clock time of the event (UTC, second precision)
+    field :occurred_at, :utc_datetime
+
+    # Optional originating IP, useful for deduplicating anonymous views.
+    # Nullable(String) for the same reason as user_id above.
+    field :ip_address, Ch, type: "Nullable(String)"
+  end
+end

lib/mixer/posts/tweet.ex

@@ -32,7 +32,7 @@ defmodule Mixer.Posts.Tweet do
   end
 
   actions do
-    defaults [:read, :destroy]
+    defaults [:read]
 
     read :following_feed do
       filter expr(
@@ -66,6 +66,49 @@ defmodule Mixer.Posts.Tweet do
             end)
         end
       end
+
+      # Track post / comment creation metrics.
+      # Root tweets emit a "post" event recorded against their own ID.
+      # Replies emit a "comment" event recorded against the parent tweet ID so
+      # that `get_summary/1` can count how many replies a tweet has received.
+      change fn changeset, context ->
+        parent_tweet_id = Ash.Changeset.get_attribute(changeset, :parent_tweet_id)
+        user_id = context.actor && context.actor.id
+
+        Ash.Changeset.after_action(changeset, fn _changeset, tweet ->
+          if parent_tweet_id do
+            Mixer.Metrics.track_comment(parent_tweet_id, user_id: user_id)
+          else
+            Mixer.Metrics.track_post(tweet.id, user_id: user_id)
+          end
+
+          {:ok, tweet}
+        end)
+      end
+    end
+
+    # Explicit destroy so we can attach a metrics hook. The policy and cascade
+    # behaviour are identical to the previous default :destroy action.
+    destroy :destroy do
+      require_atomic? false
+
+      change fn changeset, context ->
+        # Capture the record's identity *before* deletion — after the action
+        # completes the row no longer exists.
+        tweet_id = changeset.data.id
+        parent_tweet_id = changeset.data.parent_tweet_id
+        user_id = context.actor && context.actor.id
+
+        Ash.Changeset.after_action(changeset, fn _changeset, result ->
+          if parent_tweet_id do
+            Mixer.Metrics.track_delete_comment(parent_tweet_id, user_id: user_id)
+          else
+            Mixer.Metrics.track_delete_post(tweet_id, user_id: user_id)
+          end
+
+          {:ok, result}
+        end)
+      end
     end
 
     update :update do
@@ -80,6 +123,7 @@ defmodule Mixer.Posts.Tweet do
         Ash.Changeset.after_action(changeset, fn _changeset, tweet ->
           case ensure_like(tweet, context.actor) do
             {:created, _like} ->
+              Mixer.Metrics.track_like(tweet.id, user_id: context.actor && context.actor.id)
               increment_likes(tweet, context.actor)
 
             {:noop, _like} ->
@@ -100,6 +144,7 @@ defmodule Mixer.Posts.Tweet do
         Ash.Changeset.after_action(changeset, fn _changeset, tweet ->
           case remove_like(tweet, context.actor) do
             {:deleted, _like} ->
+              Mixer.Metrics.track_unlike(tweet.id, user_id: context.actor && context.actor.id)
               decrement_likes(tweet, context.actor)
 
             {:noop, _like} ->

lib/mixer_web/controllers/page_controller.ex

@@ -16,6 +16,8 @@ defmodule MixerWeb.PageController do
   end
 
   def show(conn, %{"tweet_id" => tweet_id}) do
+    user_id = conn.assigns[:current_user] && conn.assigns[:current_user].id
+    Mixer.Metrics.track_view(tweet_id, user_id: user_id, ip_address: conn.remote_ip)
     render_spa(conn, %{page: "tweet", tweet_id: tweet_id, user_id: nil})
   end
 

mix.exs

@@ -91,7 +91,8 @@ defmodule Mixer.MixProject do
       {:ex_aws, "~> 2.1.2"},
       {:ex_aws_s3, "~> 2.0"},
       {:hackney, "~> 1.9"},
-      {:sweet_xml, "~> 0.6"}
+      {:sweet_xml, "~> 0.6"},
+      {:ecto_ch, "~> 0.3"}
     ]
   end
 

mix.lock

@@ -20,6 +20,7 @@
   "castore": {:hex, :castore, "1.0.18", "5e43ef0ec7d31195dfa5a65a86e6131db999d074179d2ba5a8de11fe14570f55", [:mix], [], "hexpm", "f393e4fe6317829b158fb74d86eb681f737d2fe326aa61ccf6293c4104957e34"},
   "cc_precompiler": {:hex, :cc_precompiler, "0.1.11", "8c844d0b9fb98a3edea067f94f616b3f6b29b959b6b3bf25fee94ffe34364768", [:mix], [{:elixir_make, "~> 0.7", [hex: :elixir_make, repo: "hexpm", optional: false]}], "hexpm", "3427232caf0835f94680e5bcf082408a70b48ad68a5f5c0b02a3bea9f3a075b9"},
   "certifi": {:hex, :certifi, "2.15.0", "0e6e882fcdaaa0a5a9f2b3db55b1394dba07e8d6d9bcad08318fb604c6839712", [:rebar3], [], "hexpm", "b147ed22ce71d72eafdad94f055165c1c182f61a2ff49df28bcc71d1d5b94a60"},
+  "ch": {:hex, :ch, "0.7.1", "116c08094b30d095c3bd6a8fe4ebe19fdaaf3dce84e2413cfdd6af157baf6303", [:mix], [{:db_connection, "~> 2.9.0", [hex: :db_connection, repo: "hexpm", optional: false]}, {:decimal, "~> 2.0", [hex: :decimal, repo: "hexpm", optional: false]}, {:ecto, "~> 3.13.0", [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", "3c1c900291ff9c4c077cd1dc0c265051a3f1d26320d58b37ed9e91b33d41a868"},
   "cinder": {:hex, :cinder, "0.12.1", "02ae4988e025fb32c37e4e7f2e491586b952918c0dd99d856da13271cd680e16", [:mix], [{:ash, "~> 3.0", [hex: :ash, repo: "hexpm", optional: false]}, {:ash_phoenix, "~> 2.3", [hex: :ash_phoenix, repo: "hexpm", optional: false]}, {:gettext, "~> 1.0.0", [hex: :gettext, repo: "hexpm", optional: false]}, {:phoenix_live_view, "~> 1.0", [hex: :phoenix_live_view, repo: "hexpm", optional: false]}, {:spark, "~> 2.0", [hex: :spark, repo: "hexpm", optional: false]}], "hexpm", "a48b5677c1f57619d9d7564fb2bd7928f93750a2e8c0b1b145852a30ecf2aa20"},
   "comeonin": {:hex, :comeonin, "5.5.1", "5113e5f3800799787de08a6e0db307133850e635d34e9fab23c70b6501669510", [:mix], [], "hexpm", "65aac8f19938145377cee73973f192c5645873dcf550a8a6b18187d17c13ccdb"},
   "conv_case": {:hex, :conv_case, "0.2.3", "c1455c27d3c1ffcdd5f17f1e91f40b8a0bc0a337805a6e8302f441af17118ed8", [:mix], [], "hexpm", "88f29a3d97d1742f9865f7e394ed3da011abb7c5e8cc104e676fdef6270d4b4a"},
@@ -29,6 +30,7 @@
   "dns_cluster": {:hex, :dns_cluster, "0.2.0", "aa8eb46e3bd0326bd67b84790c561733b25c5ba2fe3c7e36f28e88f384ebcb33", [:mix], [], "hexpm", "ba6f1893411c69c01b9e8e8f772062535a4cf70f3f35bcc964a324078d8c8240"},
   "dotenvy": {:hex, :dotenvy, "1.1.1", "00e318f3c51de9fafc4b48598447e386f19204dc18ca69886905bb8f8b08b667", [:mix], [], "hexpm", "c8269471b5701e9e56dc86509c1199ded2b33dce088c3471afcfef7839766d8e"},
   "ecto": {:hex, :ecto, "3.13.5", "9d4a69700183f33bf97208294768e561f5c7f1ecf417e0fa1006e4a91713a834", [:mix], [{:decimal, "~> 2.0", [hex: :decimal, repo: "hexpm", optional: false]}, {:jason, "~> 1.0", [hex: :jason, repo: "hexpm", optional: true]}, {:telemetry, "~> 0.4 or ~> 1.0", [hex: :telemetry, repo: "hexpm", optional: false]}], "hexpm", "df9efebf70cf94142739ba357499661ef5dbb559ef902b68ea1f3c1fabce36de"},
+  "ecto_ch": {:hex, :ecto_ch, "0.8.6", "f31b507e86690c003f46e75d6e742e6b5d8ce34b6b10a86604b1c3aa785e0b56", [:mix], [{:ch, "~> 0.5.0 or ~> 0.6.0 or ~> 0.7.0", [hex: :ch, repo: "hexpm", optional: false]}, {:ecto_sql, "~> 3.13.0", [hex: :ecto_sql, repo: "hexpm", optional: false]}], "hexpm", "6ca9f1cf9680452b1925c6a3a7b5e3d8b12e38ee134b03c6a45a8b26434fad97"},
   "ecto_sql": {:hex, :ecto_sql, "3.13.5", "2f8282b2ad97bf0f0d3217ea0a6fff320ead9e2f8770f810141189d182dc304e", [:mix], [{:db_connection, "~> 2.4.1 or ~> 2.5", [hex: :db_connection, repo: "hexpm", optional: false]}, {:ecto, "~> 3.13.0", [hex: :ecto, repo: "hexpm", optional: false]}, {:myxql, "~> 0.7", [hex: :myxql, repo: "hexpm", optional: true]}, {:postgrex, "~> 0.19 or ~> 1.0", [hex: :postgrex, repo: "hexpm", optional: true]}, {:tds, "~> 2.1.1 or ~> 2.2", [hex: :tds, repo: "hexpm", optional: true]}, {:telemetry, "~> 0.4.0 or ~> 1.0", [hex: :telemetry, repo: "hexpm", optional: false]}], "hexpm", "aa36751f4e6a2b56ae79efb0e088042e010ff4935fc8684e74c23b1f49e25fdc"},
   "elixir_make": {:hex, :elixir_make, "0.9.0", "6484b3cd8c0cee58f09f05ecaf1a140a8c97670671a6a0e7ab4dc326c3109726", [:mix], [], "hexpm", "db23d4fd8b757462ad02f8aa73431a426fe6671c80b200d9710caf3d1dd0ffdb"},
   "esbuild": {:hex, :esbuild, "0.10.0", "b0aa3388a1c23e727c5a3e7427c932d89ee791746b0081bbe56103e9ef3d291f", [:mix], [{:jason, "~> 1.4", [hex: :jason, repo: "hexpm", optional: false]}], "hexpm", "468489cda427b974a7cc9f03ace55368a83e1a7be12fba7e30969af78e5f8c70"},

priv/clickhouse/migrations/.formatter.exs

@@ -0,0 +1,4 @@
+[
+  import_deps: [:ecto_ch],
+  inputs: ["*.exs"]
+]

priv/clickhouse/migrations/20260407000001_create_post_events.exs

@@ -0,0 +1,49 @@
+defmodule Mixer.ClickhouseRepo.Migrations.CreatePostEvents do
+  use Ecto.Migration
+
+  @doc """
+  Creates the `post_events` table using a MergeTree engine.
+
+  Key design decisions:
+
+  * `LowCardinality(String)` for `event_type` — the cardinality is tiny
+    (5–10 values), so ClickHouse can store it as a dictionary, giving both
+    compression and faster filtering.
+
+  * `Nullable(UUID)` / `Nullable(String)` for optional columns — ClickHouse
+    handles NULLs differently from PostgreSQL; we make the nullable fields
+    explicit so the schema is unambiguous.
+
+  * `ORDER BY (occurred_at, event_type, tweet_id)` — optimises the two most
+    common query patterns:
+      1. Time-range scans (`WHERE occurred_at >= now() - interval 24 HOUR`)
+      2. Per-tweet aggregations (`WHERE tweet_id = ?`)
+
+  * `PARTITION BY toYYYYMM(occurred_at)` — monthly partitions make it cheap
+    to drop old data with `ALTER TABLE … DROP PARTITION`.
+
+  * `TTL occurred_at + INTERVAL 1 YEAR DELETE` — automatically reclaim disk
+    space after two years. Adjust as required.
+  """
+  def up do
+    execute("""
+    CREATE TABLE IF NOT EXISTS post_events
+    (
+        event_type  LowCardinality(String),
+        tweet_id    UUID,
+        user_id     Nullable(UUID),
+        occurred_at DateTime,
+        ip_address  Nullable(String)
+    )
+    ENGINE = MergeTree()
+    PARTITION BY toYYYYMM(occurred_at)
+    ORDER BY (occurred_at, event_type, tweet_id)
+    TTL occurred_at + INTERVAL 1 YEAR DELETE
+    SETTINGS index_granularity = 8192
+    """)
+  end
+
+  def down do
+    execute("DROP TABLE IF EXISTS post_events")
+  end
+end

priv/clickhouse/seeds.exs

@@ -0,0 +1,11 @@
+# Script for populating the database. You can run it as:
+#
+#     mix run priv/clickhouse/seeds.exs
+#
+# Inside the script, you can read and write to any of your
+# repositories directly:
+#
+#     Mixer.ClickhouseRepo.insert!(%Mixer.SomeSchema{})
+#
+# We recommend using the bang functions (`insert!`, `update!`
+# and so on) as they will fail if something goes wrong.