Move strategies in their own files

This improves readability quite a bit.

4 files changed, 176 insertions, 155 deletions

diff --git a/lib/gitlab/database/count.rb b/lib/gitlab/database/count.rb
index df08e6916dd..c996d786909 100644
--- a/lib/gitlab/database/count.rb
+++ b/lib/gitlab/database/count.rb
@@ -50,161 +50,6 @@ module Gitlab
           end
         end
       end
-
-      # This strategy performs an exact count on the model.
-      #
-      # This is guaranteed to be accurate, however it also scans the
-      # whole table. Hence, there are no guarantees with respect
-      # to runtime.
-      #
-      # Note that for very large tables, this may even timeout.
-      class ExactCountStrategy
-        attr_reader :models
-        def initialize(models)
-          @models = models
-        end
-
-        def count
-          models.each_with_object({}) do |model, data|
-            data[model] = model.count
-          end
-        end
-
-        def self.enabled?
-          true
-        end
-      end
-
-      class PgClass < ActiveRecord::Base
-        self.table_name = 'pg_class'
-      end
-
-      # This strategy counts based on PostgreSQL's statistics in pg_stat_user_tables.
-      #
-      # Specifically, it relies on the column reltuples in said table. An additional
-      # check is performed to make sure statistics were updated within the last hour.
-      #
-      # Otherwise, this strategy skips tables with outdated statistics.
-      #
-      # There are no guarantees with respect to the accuracy of this strategy. Runtime
-      # however is guaranteed to be "fast", because it only looks up statistics.
-      class ReltuplesCountStrategy
-        attr_reader :models
-        def initialize(models)
-          @models = models
-        end
-
-        # Returns a hash of the table names that have recently updated tuples.
-        #
-        # @returns [Hash] Table name to count mapping (e.g. { 'projects' => 5, 'users' => 100 })
-        def count
-          size_estimates
-        rescue *CONNECTION_ERRORS
-          {}
-        end
-
-        def self.enabled?
-          Gitlab::Database.postgresql?
-        end
-
-        private
-
-        def table_names
-          models.map(&:table_name)
-        end
-
-        def size_estimates(check_statistics: true)
-          table_to_model = models.each_with_object({}) { |model, h| h[model.table_name] = model }
-
-          # Querying tuple stats only works on the primary. Due to load balancing, the
-          # easiest way to do this is to start a transaction.
-          ActiveRecord::Base.transaction do
-            get_statistics(table_names, check_statistics: check_statistics).each_with_object({}) do |row, data|
-              model = table_to_model[row.table_name]
-              data[model] = row.estimate
-            end
-          end
-        end
-
-        # Generates the PostgreSQL query to return the tuples for tables
-        # that have been vacuumed or analyzed in the last hour.
-        #
-        # @param [Array] table names
-        # @returns [Hash] Table name to count mapping (e.g. { 'projects' => 5, 'users' => 100 })
-        def get_statistics(table_names, check_statistics: true)
-          time = "to_timestamp(#{1.hour.ago.to_i})"
-
-          query = PgClass.joins("LEFT JOIN pg_stat_user_tables USING (relname)")
-            .where(relname: table_names)
-            .select('pg_class.relname AS table_name, reltuples::bigint AS estimate')
-
-          if check_statistics
-            query = query.where('last_vacuum > ? OR last_autovacuum > ? OR last_analyze > ? OR last_autoanalyze > ?',
-                                time, time, time, time)
-          end
-
-          query
-        end
-      end
-
-      # A tablesample count executes in two phases:
-      # * Estimate table sizes based on reltuples.
-      # * Based on the estimate:
-      #   * If the table is considered 'small', execute an exact relation count.
-      #   * Otherwise, count on a sample of the table using TABLESAMPLE.
-      #
-      # The size of the sample is chosen in a way that we always roughly scan
-      # the same amount of rows (see TABLESAMPLE_ROW_TARGET).
-      #
-      # There are no guarantees with respect to the accuracy of the result or runtime.
-      class TablesampleCountStrategy < ReltuplesCountStrategy
-        EXACT_COUNT_THRESHOLD = 100_000
-        TABLESAMPLE_ROW_TARGET = 100_000
-
-        def count
-          estimates = size_estimates(check_statistics: false)
-
-          models.each_with_object({}) do |model, count_by_model|
-            count = perform_count(model, estimates[model])
-            count_by_model[model] = count if count
-          end
-        rescue *CONNECTION_ERRORS
-          {}
-        end
-
-        def self.enabled?
-          Gitlab::Database.postgresql? && Feature.enabled?(:tablesample_counts)
-        end
-
-        private
-
-        def perform_count(model, estimate)
-          # If we estimate 0, we may not have statistics at all. Don't use them.
-          return nil unless estimate && estimate > 0
-
-          if estimate < EXACT_COUNT_THRESHOLD
-            # The table is considered small, the assumption here is that
-            # the exact count will be fast anyways.
-            model.count
-          else
-            # The table is considered large, let's only count on a sample.
-            tablesample_count(model, estimate)
-          end
-        end
-
-        def tablesample_count(model, estimate)
-          portion = (TABLESAMPLE_ROW_TARGET.to_f / estimate).round(4)
-          inverse = 1 / portion
-          query = <<~SQL
-            SELECT (COUNT(*)*#{inverse})::integer AS count
-            FROM #{model.table_name} TABLESAMPLE SYSTEM (#{portion * 100})
-          SQL
-
-          rows = ActiveRecord::Base.connection.select_all(query)
-
-          Integer(rows.first['count'])
-        end
-      end
     end
   end
 end
diff --git a/lib/gitlab/database/count/exact_count_strategy.rb b/lib/gitlab/database/count/exact_count_strategy.rb
new file mode 100644
index 00000000000..0276fe2b54f
--- /dev/null
+++ b/lib/gitlab/database/count/exact_count_strategy.rb
@@ -0,0 +1,31 @@
+# frozen_string_literal: true
+
+module Gitlab
+  module Database
+    module Count
+      # This strategy performs an exact count on the model.
+      #
+      # This is guaranteed to be accurate, however it also scans the
+      # whole table. Hence, there are no guarantees with respect
+      # to runtime.
+      #
+      # Note that for very large tables, this may even timeout.
+      class ExactCountStrategy
+        attr_reader :models
+        def initialize(models)
+          @models = models
+        end
+
+        def count
+          models.each_with_object({}) do |model, data|
+            data[model] = model.count
+          end
+        end
+
+        def self.enabled?
+          true
+        end
+      end
+    end
+  end
+end
diff --git a/lib/gitlab/database/count/reltuples_count_strategy.rb b/lib/gitlab/database/count/reltuples_count_strategy.rb
new file mode 100644
index 00000000000..c3a674aeb7e
--- /dev/null
+++ b/lib/gitlab/database/count/reltuples_count_strategy.rb
@@ -0,0 +1,79 @@
+# frozen_string_literal: true
+
+module Gitlab
+  module Database
+    module Count
+      class PgClass < ActiveRecord::Base
+        self.table_name = 'pg_class'
+      end
+
+      # This strategy counts based on PostgreSQL's statistics in pg_stat_user_tables.
+      #
+      # Specifically, it relies on the column reltuples in said table. An additional
+      # check is performed to make sure statistics were updated within the last hour.
+      #
+      # Otherwise, this strategy skips tables with outdated statistics.
+      #
+      # There are no guarantees with respect to the accuracy of this strategy. Runtime
+      # however is guaranteed to be "fast", because it only looks up statistics.
+      class ReltuplesCountStrategy
+        attr_reader :models
+        def initialize(models)
+          @models = models
+        end
+
+        # Returns a hash of the table names that have recently updated tuples.
+        #
+        # @returns [Hash] Table name to count mapping (e.g. { 'projects' => 5, 'users' => 100 })
+        def count
+          size_estimates
+        rescue *CONNECTION_ERRORS
+          {}
+        end
+
+        def self.enabled?
+          Gitlab::Database.postgresql?
+        end
+
+        private
+
+        def table_names
+          models.map(&:table_name)
+        end
+
+        def size_estimates(check_statistics: true)
+          table_to_model = models.each_with_object({}) { |model, h| h[model.table_name] = model }
+
+          # Querying tuple stats only works on the primary. Due to load balancing, the
+          # easiest way to do this is to start a transaction.
+          ActiveRecord::Base.transaction do
+            get_statistics(table_names, check_statistics: check_statistics).each_with_object({}) do |row, data|
+              model = table_to_model[row.table_name]
+              data[model] = row.estimate
+            end
+          end
+        end
+
+        # Generates the PostgreSQL query to return the tuples for tables
+        # that have been vacuumed or analyzed in the last hour.
+        #
+        # @param [Array] table names
+        # @returns [Hash] Table name to count mapping (e.g. { 'projects' => 5, 'users' => 100 })
+        def get_statistics(table_names, check_statistics: true)
+          time = 1.hour.ago
+
+          query = PgClass.joins("LEFT JOIN pg_stat_user_tables USING (relname)")
+            .where(relname: table_names)
+            .select('pg_class.relname AS table_name, reltuples::bigint AS estimate')
+
+          if check_statistics
+            query = query.where('last_vacuum > ? OR last_autovacuum > ? OR last_analyze > ? OR last_autoanalyze > ?',
+                                time, time, time, time)
+          end
+
+          query
+        end
+      end
+    end
+  end
+end
diff --git a/lib/gitlab/database/count/tablesample_count_strategy.rb b/lib/gitlab/database/count/tablesample_count_strategy.rb
new file mode 100644
index 00000000000..c211bb5bb16
--- /dev/null
+++ b/lib/gitlab/database/count/tablesample_count_strategy.rb
@@ -0,0 +1,66 @@
+# frozen_string_literal: true
+
+module Gitlab
+  module Database
+    module Count
+      # A tablesample count executes in two phases:
+      # * Estimate table sizes based on reltuples.
+      # * Based on the estimate:
+      #   * If the table is considered 'small', execute an exact relation count.
+      #   * Otherwise, count on a sample of the table using TABLESAMPLE.
+      #
+      # The size of the sample is chosen in a way that we always roughly scan
+      # the same amount of rows (see TABLESAMPLE_ROW_TARGET).
+      #
+      # There are no guarantees with respect to the accuracy of the result or runtime.
+      class TablesampleCountStrategy < ReltuplesCountStrategy
+        EXACT_COUNT_THRESHOLD = 100_000
+        TABLESAMPLE_ROW_TARGET = 100_000
+
+        def count
+          estimates = size_estimates(check_statistics: false)
+
+          models.each_with_object({}) do |model, count_by_model|
+            count = perform_count(model, estimates[model])
+            count_by_model[model] = count if count
+          end
+        rescue *CONNECTION_ERRORS
+          {}
+        end
+
+        def self.enabled?
+          Gitlab::Database.postgresql? && Feature.enabled?(:tablesample_counts)
+        end
+
+        private
+
+        def perform_count(model, estimate)
+          # If we estimate 0, we may not have statistics at all. Don't use them.
+          return nil unless estimate && estimate > 0
+
+          if estimate < EXACT_COUNT_THRESHOLD
+            # The table is considered small, the assumption here is that
+            # the exact count will be fast anyways.
+            model.count
+          else
+            # The table is considered large, let's only count on a sample.
+            tablesample_count(model, estimate)
+          end
+        end
+
+        def tablesample_count(model, estimate)
+          portion = (TABLESAMPLE_ROW_TARGET.to_f / estimate).round(4)
+          inverse = 1 / portion
+          query = <<~SQL
+            SELECT (COUNT(*)*#{inverse})::integer AS count
+            FROM #{model.table_name} TABLESAMPLE SYSTEM (#{portion * 100})
+          SQL
+
+          rows = ActiveRecord::Base.connection.select_all(query)
+
+          Integer(rows.first['count'])
+        end
+      end
+    end
+  end
+end