feat(Database::Videos): built-in video cache and support for multiple caching backends

I did this to get rid of Redis compatible DBs and for speed purposes.
This is considered experimental, but everything works fine from
what I have tested.

Here are some benchmarks using the built-in benchmark library of
crystal:

\# built-in release
cache get  19.79M ( 50.54ns) (± 4.12%)  32.0B/op  fastest
cache insert   7.88k (126.86µs) (± 2.20%)  65.5kB/op  fastest
cache get   4.31k (232.11µs) (± 5.50%)  104kB/op  fastest

\# redis release
cache get  22.27k ( 44.90µs) (± 6.40%)  264B/op  fastest
cache insert   4.74k (211.01µs) (± 4.72%)  65.7kB/op  fastest
cache get   2.51k (399.11µs) (±13.15%)  129kB/op  fastest

---

OP/s are way higher, and memory usage per call is lower, so it's a win
win.

src/invidious.cr

@@ -156,19 +156,6 @@ end
 OUTPUT = CONFIG.output.upcase == "STDOUT" ? STDOUT : File.open(CONFIG.output, mode: "a")
 LOGGER = Invidious::LogHandler.new(OUTPUT, CONFIG.log_level, CONFIG.colorize_logs)
 
-REDIS_DB = begin
-  LOGGER.info "Connecting to Redis compatible DB"
-  redis = Redis::PooledClient.new(unixsocket: CONFIG.redis_socket || nil, url: CONFIG.redis_url || nil)
-  if redis.ping
-    LOGGER.info "Connected to Redis compatible DB via unix domain socket at '#{CONFIG.redis_socket}'" if CONFIG.redis_socket
-    LOGGER.info "Connected to Redis compatible DB via TCP socket at '#{CONFIG.redis_url}'" if CONFIG.redis_url
-  end
-  redis
-rescue ex
-  LOGGER.error "Failed to connect to a Redis compatible DB. Invidious will store the video cache on the PostgresSQL DB"
-  nil
-end
-
 # Check table integrity
 Invidious::Database.check_integrity(CONFIG)
 

src/invidious/config.cr

@@ -217,7 +217,16 @@ class Config
 
   property tokens_server : String = ""
 
-  property video_cache : Bool = true
+  property video_cache : VideoCacheConfig
+
+  class VideoCacheConfig
+    include YAML::Serializable
+
+    property enabled : Bool = true
+    property backend : Int32 = 1
+    # Max quantity of keys that can be held on the LRU cache
+    property lru_max_size : Int32 = 18432 # ~512MB
+  end
 
   {% if flag?(:linux) %}
     property reload_config_automatically : Bool = true
@@ -395,6 +404,16 @@ class Config
       end
     end
 
+    if config.video_cache.enabled
+      if !config.video_cache.backend.in?(0, 1, 2)
+        puts "Config: 'video_cache_storage', can only be:"
+        puts "0 (PostgreSQL)"
+        puts "1 (Redis compatible DB) (Default)"
+        puts "2 (In memory LRU)"
+        exit(1)
+      end
+    end
+
     return config
   end
 end

src/invidious/database/videos.cr

@@ -1,42 +1,63 @@
 require "./base.cr"
+require "redis"
+
+VideoCache = Invidious::Database::Videos::Cache.new
 
 module Invidious::Database::Videos
-  module DBCache
-    extend self
+  class Cache
+    def initialize
+      case CONFIG.video_cache.backend
+      when 0
+        @cache = CacheMethods::PostgresSQL.new
+      when 1
+        @cache = CacheMethods::Redis_.new
+      when 2
+        @cache = CacheMethods::LRU.new
+      else
+        LOGGER.debug "Video Cache: Using default cache method to store video cache (PostgreSQL)"
+        @cache = CacheMethods::PostgresSQL.new
+      end
+    end
 
     def set(video : Video, expire_time)
-      if redis = REDIS_DB
-        redis.set(video.id, video.info.to_json, expire_time)
-        redis.set(video.id + ":time", video.updated, expire_time)
-      else
-        request = <<-SQL
-          INSERT INTO videos
-          VALUES ($1, $2, $3)
-          ON CONFLICT (id) DO NOTHING
-        SQL
-
-        PG_DB.exec(request, video.id, video.info.to_json, video.updated)
-      end
+      @cache.set(video, expire_time)
     end
 
     def del(id : String)
-      if redis = REDIS_DB
-        redis.del(id)
-        redis.del(id + ":time")
-      else
-        request = <<-SQL
-          DELETE FROM videos *
-          WHERE id = $1
-        SQL
-
-        PG_DB.exec(request, id)
-      end
+      @cache.del(id)
     end
 
     def get(id : String)
-      if redis = REDIS_DB
-        info = redis.get(id)
-        time = redis.get(id + ":time")
+      return @cache.get(id)
+    end
+  end
+
+  module CacheMethods
+    # TODO: Save the cache on a file with a Job
+    class LRU
+      @max_size : Int32
+      @lru = {} of String => String
+      @access = [] of String
+
+      def initialize(@max_size = CONFIG.video_cache.lru_max_size)
+        LOGGER.info "Video Cache: Using in memory LRU to store video cache"
+        LOGGER.info "Video Cache, LRU: LRU cache max size set to #{@max_size}"
+      end
+
+      # TODO: Handle expire_time with a Job
+      def set(video : Video, expire_time)
+        self[video.id] = video.info.to_json
+        self[video.id + ":time"] = "#{video.updated}"
+      end
+
+      def del(id : String)
+        self.delete(id)
+        self.delete(id + ":time")
+      end
+
+      def get(id : String)
+        info = self[id]
+        time = self[id + ":time"]
         if info && time
           return Video.new({
             id:      id,
@@ -46,7 +67,98 @@ module Invidious::Database::Videos
         else
           return nil
         end
-      else
+      end
+
+      private def [](key)
+        if @lru[key]?
+          @access.delete(key)
+          @access.push(key)
+          @lru[key]
+        else
+          nil
+        end
+      end
+
+      private def []=(key, value)
+        if @lru.size >= @max_size
+          lru_key = @access.shift
+          @lru.delete(lru_key)
+        end
+        @lru[key] = value
+        @access.push(key)
+      end
+
+      private def delete(key)
+        if @lru[key]?
+          @lru.delete(key)
+          @access.delete(key)
+        end
+      end
+    end
+
+    class Redis_
+      @redis : Redis::PooledClient
+
+      def initialize
+        @redis = Redis::PooledClient.new(unixsocket: CONFIG.redis_socket || nil, url: CONFIG.redis_url || nil)
+        LOGGER.info "Video Cache: Using Redis compatible DB to store video cache"
+        LOGGER.info "Connecting to Redis compatible DB"
+        if @redis.ping
+          LOGGER.info "Connected to Redis compatible DB via unix domain socket at '#{CONFIG.redis_socket}'" if CONFIG.redis_socket
+          LOGGER.info "Connected to Redis compatible DB via TCP socket at '#{CONFIG.redis_url}'" if CONFIG.redis_url
+        end
+      end
+
+      def set(video : Video, expire_time)
+        @redis.set(video.id, video.info.to_json, expire_time)
+        @redis.set(video.id + ":time", video.updated, expire_time)
+      end
+
+      def del(id : String)
+        @redis.del(id)
+        @redis.del(id + ":time")
+      end
+
+      def get(id : String)
+        info = @redis.get(id)
+        time = @redis.get(id + ":time")
+        if info && time
+          return Video.new({
+            id:      id,
+            info:    JSON.parse(info).as_h,
+            updated: Time.parse(time, "%Y-%m-%d %H:%M:%S %z", Time::Location::UTC),
+          })
+        else
+          return nil
+        end
+      end
+    end
+
+    class PostgresSQL
+      def initialize
+        LOGGER.info "Video Cache: Using PostgreSQL to store video cache"
+      end
+
+      def set(video : Video, expire_time)
+        request = <<-SQL
+          INSERT INTO videos
+          VALUES ($1, $2, $3)
+          ON CONFLICT (id) DO NOTHING
+        SQL
+
+        PG_DB.exec(request, video.id, video.info.to_json, video.updated)
+      end
+
+      def del(id)
+        request = <<-SQL
+          DELETE FROM videos *
+          WHERE id = $1
+        SQL
+
+        PG_DB.exec(request, id)
+      end
+
+      def get(id : String) : Video?
         request = <<-SQL
           SELECT * FROM videos
           WHERE id = $1
@@ -60,11 +172,11 @@ module Invidious::Database::Videos
   extend self
 
   def insert(video : Video)
-    DBCache.set(video: video, expire_time: 14400) if CONFIG.video_cache
+    VideoCache.set(video: video, expire_time: 14400) if CONFIG.video_cache.enabled
   end
 
   def delete(id)
-    DBCache.del(id)
+    VideoCache.del(id)
   end
 
   def delete_expired
@@ -87,6 +199,6 @@ module Invidious::Database::Videos
   end
 
   def select(id : String) : Video?
-    return DBCache.get(id)
+    return VideoCache.get(id)
   end
 end