add caching to expensive queries

CHANGELOG.md

@@ -9,6 +9,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added
 
+- Add caching to graph + instance endpoints to better handle traffic spikes.
+
 ### Changed
 
 ### Deprecated

backend/config/config.exs

@@ -34,10 +34,15 @@ config :logger, :console,
 config :phoenix, :json_library, Jason
 
 config :gollum,
+  # 24 hrs
   refresh_secs: 86_400,
   lazy_refresh: true,
   user_agent: "fediverse.space crawler"
 
+config :backend, Graph.Cache,
+  # 1 hour
+  gc_interval: 3600
+
 config :ex_twilio,
   account_sid: System.get_env("TWILIO_ACCOUNT_SID"),
   auth_token: System.get_env("TWILIO_AUTH_TOKEN")

backend/lib/backend/application.ex

@@ -33,7 +33,8 @@ defmodule Backend.Application do
       ),
       Supervisor.child_spec({Task, fn -> HTTPoison.start() end}, id: :start_httpoison),
       Backend.Scheduler,
-      Backend.Elasticsearch.Cluster
+      Backend.Elasticsearch.Cluster,
+      Graph.Cache
     ]
 
     children =

backend/lib/backend_web/controllers/graph_controller.ex

@@ -1,19 +1,16 @@
 defmodule BackendWeb.GraphController do
   use BackendWeb, :controller
-
-  alias Backend.Api
+  alias Graph.Cache
 
   action_fallback BackendWeb.FallbackController
 
   def index(conn, _params) do
-    nodes = Api.list_nodes()
-    edges = Api.list_edges()
+    %{nodes: nodes, edges: edges} = Cache.get_graph()
     render(conn, "index.json", nodes: nodes, edges: edges)
   end
 
   def show(conn, %{"id" => domain}) do
-    nodes = Api.list_nodes(domain)
-    edges = Api.list_edges(domain)
+    %{nodes: nodes, edges: edges} = Cache.get_graph(domain)
     render(conn, "index.json", nodes: nodes, edges: edges)
   end
 end

backend/lib/backend_web/controllers/instance_controller.ex

@@ -2,17 +2,17 @@ defmodule BackendWeb.InstanceController do
   use BackendWeb, :controller
 
   import Backend.Util
-  alias Backend.Api
+  alias Graph.Cache
 
   action_fallback(BackendWeb.FallbackController)
 
   def show(conn, %{"id" => domain}) do
-    instance = Api.get_instance_with_peers(domain)
+    instance = Cache.get_instance_with_peers(domain)
 
     if instance == nil or instance.opt_out == true do
       send_resp(conn, 404, "Not found")
     else
-      last_crawl = get_last_crawl(domain)
+      last_crawl = Cache.get_last_crawl(domain)
       render(conn, "show.json", instance: instance, crawl: last_crawl)
     end
   end

backend/lib/graph/cache.ex

@@ -0,0 +1,93 @@
+defmodule Graph.Cache do
+  @moduledoc false
+  use Nebulex.Cache,
+    otp_app: :backend,
+    adapter: Nebulex.Adapters.Local
+
+  alias Backend.{Api, Crawl, Edge, Instance, MostRecentCrawl, Repo}
+  alias __MODULE__
+  require Logger
+  import Ecto.Query
+
+  @spec get_graph(String.t() | nil) :: %{
+          nodes: [Instance.t()],
+          edges: [Edge.t()]
+        }
+  def get_graph(domain \\ nil) do
+    key =
+      if domain != nil do
+        "graph_" <> domain
+      else
+        "graph"
+      end
+
+    case Cache.get(key) do
+      nil ->
+        Appsignal.increment_counter("graph_cache.misses", 1)
+        Logger.debug("Graph cache: miss")
+        nodes = Api.list_nodes(domain)
+        edges = Api.list_edges(domain)
+        # Cache for 10 minutes
+        Cache.set(key, %{nodes: nodes, edges: edges}, ttl: 600)
+        %{nodes: nodes, edges: edges}
+
+      data ->
+        Appsignal.increment_counter("graph_cache.hits", 1)
+        Logger.debug("Graph cache: hit")
+        data
+    end
+  end
+
+  @spec get_instance_with_peers(String.t()) :: Instance.t()
+  def get_instance_with_peers(domain) do
+    key = "instance_" <> domain
+
+    case Cache.get(key) do
+      nil ->
+        Appsignal.increment_counter("instance_cache.misses", 1)
+        Logger.debug("Instance cache: miss")
+        instance = Api.get_instance_with_peers(domain)
+        # Cache for one minute
+        Cache.set(key, instance, ttl: 60)
+        instance
+
+      data ->
+        Appsignal.increment_counter("instance_cache.hits", 1)
+        Logger.debug("Instance cache: hit")
+        data
+    end
+  end
+
+  @spec get_last_crawl(String.t()) :: Crawl.t() | nil
+  def get_last_crawl(domain) do
+    key = "most_recent_crawl_" <> domain
+
+    most_recent_crawl_subquery =
+      MostRecentCrawl
+      |> select([mrc], %{
+        most_recent_id: mrc.crawl_id
+      })
+      |> where([mrc], mrc.instance_domain == ^domain)
+
+    case Cache.get(key) do
+      nil ->
+        Appsignal.increment_counter("most_recent_crawl_cache.misses", 1)
+        Logger.debug("Most recent crawl cache: miss")
+
+        crawl =
+          Crawl
+          |> join(:inner, [c], mrc in subquery(most_recent_crawl_subquery),
+            on: c.id == mrc.most_recent_id
+          )
+          |> Repo.one()
+
+        # Cache for one minute
+        Cache.set(key, crawl, ttl: 60)
+
+      data ->
+        Appsignal.increment_counter("most_recent_crawl_cache.hits", 1)
+        Logger.debug("Most recent crawl cache: hit")
+        data
+    end
+  end
+end

backend/mix.exs

@@ -63,7 +63,8 @@ defmodule Backend.MixProject do
       {:ex_twilio, "~> 0.7.0"},
       {:elasticsearch, "~> 1.0"},
       {:appsignal, "~> 1.10.1"},
-      {:credo, "~> 1.1", only: [:dev, :test], runtime: false}
+      {:credo, "~> 1.1", only: [:dev, :test], runtime: false},
+      {:nebulex, "~> 1.1"}
     ]
   end
 

backend/mix.lock

@@ -35,6 +35,7 @@
   "metrics": {:hex, :metrics, "1.0.1", "25f094dea2cda98213cecc3aeff09e940299d950904393b2a29d191c346a8486", [:rebar3], [], "hexpm"},
   "mime": {:hex, :mime, "1.3.1", "30ce04ab3175b6ad0bdce0035cba77bba68b813d523d1aac73d9781b4d193cf8", [:mix], [], "hexpm"},
   "mimerl": {:hex, :mimerl, "1.2.0", "67e2d3f571088d5cfd3e550c383094b47159f3eee8ffa08e64106cdf5e981be3", [:rebar3], [], "hexpm"},
+  "nebulex": {:hex, :nebulex, "1.1.0", "be45cc3a2b7d01eb7da05747d38072d336187d05796ad9ef2d9dad9be430f915", [:mix], [{:shards, "~> 0.6", [hex: :shards, repo: "hexpm", optional: false]}], "hexpm"},
   "paginator": {:hex, :paginator, "0.6.0", "bc2c01abdd98281ff39b6a7439cf540091122a7927bdaabc167c61d4508f9cbb", [:mix], [{:ecto, "~> 3.0", [hex: :ecto, repo: "hexpm", optional: false]}, {:ecto_sql, "~> 3.0", [hex: :ecto_sql, repo: "hexpm", optional: false]}, {:postgrex, "~> 0.13", [hex: :postgrex, repo: "hexpm", optional: true]}], "hexpm"},
   "parse_trans": {:hex, :parse_trans, "3.3.0", "09765507a3c7590a784615cfd421d101aec25098d50b89d7aa1d66646bc571c1", [:rebar3], [], "hexpm"},
   "phoenix": {:hex, :phoenix, "1.4.9", "746d098e10741c334d88143d3c94cab1756435f94387a63441792e66ec0ee974", [:mix], [{:jason, "~> 1.0", [hex: :jason, repo: "hexpm", optional: true]}, {:phoenix_pubsub, "~> 1.1", [hex: :phoenix_pubsub, repo: "hexpm", optional: false]}, {:plug, "~> 1.8.1 or ~> 1.9", [hex: :plug, repo: "hexpm", optional: false]}, {:plug_cowboy, "~> 1.0 or ~> 2.0", [hex: :plug_cowboy, repo: "hexpm", optional: true]}, {:telemetry, "~> 0.4", [hex: :telemetry, repo: "hexpm", optional: false]}], "hexpm"},
@@ -48,6 +49,7 @@
   "public_suffix": {:hex, :public_suffix, "0.6.0", "100cfe86f13f9f6f0cf67e743b1b83c78dd1223a2c422fa03ebf4adff514cbc3", [:mix], [{:idna, ">= 1.2.0 and < 6.0.0", [hex: :idna, repo: "hexpm", optional: false]}], "hexpm"},
   "quantum": {:hex, :quantum, "2.3.4", "72a0e8855e2adc101459eac8454787cb74ab4169de6ca50f670e72142d4960e9", [:mix], [{:calendar, "~> 0.17", [hex: :calendar, repo: "hexpm", optional: true]}, {:crontab, "~> 1.1", [hex: :crontab, repo: "hexpm", optional: false]}, {:gen_stage, "~> 0.12", [hex: :gen_stage, repo: "hexpm", optional: false]}, {:swarm, "~> 3.3", [hex: :swarm, repo: "hexpm", optional: false]}, {:timex, "~> 3.1", [hex: :timex, repo: "hexpm", optional: true]}], "hexpm"},
   "ranch": {:hex, :ranch, "1.7.1", "6b1fab51b49196860b733a49c07604465a47bdb78aa10c1c16a3d199f7f8c881", [:rebar3], [], "hexpm"},
+  "shards": {:hex, :shards, "0.6.0", "678d292ad74a4598a872930f9b12251f43e97f6050287f1fb712fbfd3d282f75", [:make, :rebar3], [], "hexpm"},
   "sobelow": {:hex, :sobelow, "0.8.0", "a3ec73e546dfde19f14818e5000c418e3f305d9edb070e79dd391de0ae1cd1ea", [:mix], [], "hexpm"},
   "ssl_verify_fun": {:hex, :ssl_verify_fun, "1.1.4", "f0eafff810d2041e93f915ef59899c923f4568f4585904d010387ed74988e77b", [:make, :mix, :rebar3], [], "hexpm"},
   "swarm": {:hex, :swarm, "3.4.0", "64f8b30055d74640d2186c66354b33b999438692a91be275bb89cdc7e401f448", [:mix], [{:gen_state_machine, "~> 2.0", [hex: :gen_state_machine, repo: "hexpm", optional: false]}, {:libring, "~> 1.0", [hex: :libring, repo: "hexpm", optional: false]}], "hexpm"},