PERF: Active Record #pluck is twice faster

PERF: SqlBuilder bypasses AR converters and uses PG directly

lib/freedom_patches/fast_pluck.rb

@@ -0,0 +1,108 @@
+# Speeds up #pluck so its about 2.2x faster, importantly makes pluck avoid creation of a slew
+# of AR objects
+
+require_dependency 'sql_builder'
+
+class ActiveRecord::Relation
+
+  # class RailsDateTimeDecoder < PG::SimpleDecoder
+  #   def decode(string, tuple=nil, field=nil)
+  #     if Rails.version >= "4.2.0"
+  #       @caster ||= ActiveRecord::Type::DateTime.new
+  #       @caster.type_cast_from_database(string)
+  #     else
+  #       ActiveRecord::ConnectionAdapters::Column.string_to_time string
+  #     end
+  #   end
+  # end
+  #
+  # class ActiveRecordTypeMap < PG::BasicTypeMapForResults
+  #   def initialize(connection)
+  #     super(connection)
+  #     rm_coder 0, 1114
+  #     add_coder RailsDateTimeDecoder.new(name: "timestamp", oid: 1114, format: 0)
+  #     # we don't need deprecations
+  #     self.default_type_map = PG::TypeMapInRuby.new
+  #   end
+  # end
+  #
+  # def self.pg_type_map
+  #   conn = ActiveRecord::Base.connection.raw_connection
+  #   @typemap ||= ActiveRecordTypeMap.new(conn)
+  # end
+
+  class ::ActiveRecord::ConnectionAdapters::PostgreSQLAdapter
+    if Rails.version >= "4.2.0"
+      def select_raw(arel, name = nil, binds = [], &block)
+        arel, binds = binds_from_relation arel, binds
+        sql = to_sql(arel, binds)
+        execute_and_clear(sql, name, binds, &block)
+      end
+    else
+
+      def select_raw(arel, name = nil, binds = [], &block)
+        arel, binds = binds_from_relation arel, binds
+        sql = to_sql(arel, binds)
+
+        result = without_prepared_statement?(binds) ? exec_no_cache(sql, 'SQL', binds) :
+                                                        exec_cache(sql, 'SQL', binds)
+        yield result, nil
+      end
+    end
+  end
+
+  def pluck(*cols)
+
+    conn = ActiveRecord::Base.connection
+    relation = self
+
+    cols.map! do |column_name|
+      if column_name.is_a?(Symbol) && attribute_alias?(column_name)
+        attribute_alias(column_name)
+      else
+        column_name.to_s
+      end
+    end
+
+
+    if has_include?(cols.first)
+      construct_relation_for_association_calculations.pluck(*cols)
+    else
+      relation = spawn
+
+      relation.select_values = cols.map { |cn|
+        columns_hash.key?(cn) ? arel_table[cn] : cn
+      }
+
+      conn.select_raw(relation) do |result,_|
+        result.type_map = SqlBuilder.pg_type_map
+        result.nfields == 1 ? result.column_values(0) : result.values
+      end
+
+    end
+  end
+end
+
+# require 'benchmark/ips'
+#
+# ENV['RAILS_ENV'] = 'production'
+# require File.expand_path("../../config/environment", __FILE__)
+#
+# Benchmark.ips do |x|
+#   x.report("fast_pluck") do
+#     Post.where(topic_id: 48464).fast_pluck(:id)
+#   end
+#
+#   x.report("pluck") do
+#     Post.where(topic_id: 48464).pluck(:id)
+#   end
+# end
+#
+# % ruby tmp/fast_pluck.rb
+# Calculating -------------------------------------
+#           fast_pluck   165.000  i/100ms
+#                pluck    80.000  i/100ms
+# -------------------------------------------------
+#           fast_pluck      1.720k (± 8.8%) i/s -      8.580k
+#                pluck    807.913  (± 4.0%) i/s -      4.080k
+#