Implement batch counter for summing a column

lib/gitlab/database/batch_count.rb

@@ -16,6 +16,7 @@
 #  batch_count(::Clusters::Cluster.aws_installed.enabled, :cluster_id)
 #  batch_distinct_count(::Project, :creator_id)
 #  batch_distinct_count(::Project.with_active_services.service_desk_enabled.where(time_period), start: ::User.minimum(:id), finish: ::User.maximum(:id))
+#  batch_sum(User, :sign_in_count)
 module Gitlab
   module Database
     module BatchCount
@@ -27,6 +28,10 @@ module Gitlab
         BatchCounter.new(relation, column: column).count(mode: :distinct, batch_size: batch_size, start: start, finish: finish)
       end
 
+      def batch_sum(relation, column, batch_size: nil, start: nil, finish: nil)
+        BatchCounter.new(relation, column: nil, operation: :sum, operation_args: [column]).count(batch_size: batch_size, start: start, finish: finish)
+      end
+
       class << self
         include BatchCount
       end
@@ -35,6 +40,7 @@ module Gitlab
     class BatchCounter
       FALLBACK = -1
       MIN_REQUIRED_BATCH_SIZE = 1_250
+      DEFAULT_SUM_BATCH_SIZE = 1_000
       MAX_ALLOWED_LOOPS = 10_000
       SLEEP_TIME_IN_SECONDS = 0.01 # 10 msec sleep
       ALLOWED_MODES = [:itself, :distinct].freeze
@@ -43,13 +49,16 @@ module Gitlab
       DEFAULT_DISTINCT_BATCH_SIZE = 10_000
       DEFAULT_BATCH_SIZE = 100_000
 
-      def initialize(relation, column: nil)
+      def initialize(relation, column: nil, operation: :count, operation_args: nil)
         @relation = relation
         @column = column || relation.primary_key
+        @operation = operation
+        @operation_args = operation_args
       end
 
       def unwanted_configuration?(finish, batch_size, start)
-        batch_size <= MIN_REQUIRED_BATCH_SIZE ||
+        (@operation == :count && batch_size <= MIN_REQUIRED_BATCH_SIZE) ||
+          (@operation == :sum && batch_size < DEFAULT_SUM_BATCH_SIZE) ||
           (finish - start) / batch_size >= MAX_ALLOWED_LOOPS ||
           start > finish
       end
@@ -60,7 +69,7 @@ module Gitlab
         check_mode!(mode)
 
         # non-distinct have better performance
-        batch_size ||= mode == :distinct ? DEFAULT_DISTINCT_BATCH_SIZE : DEFAULT_BATCH_SIZE
+        batch_size ||= batch_size_for_mode_and_operation(mode, @operation)
 
         start = actual_start(start)
         finish = actual_finish(finish)
@@ -91,11 +100,17 @@ module Gitlab
 
       def batch_fetch(start, finish, mode)
         # rubocop:disable GitlabSecurity/PublicSend
-        @relation.select(@column).public_send(mode).where(between_condition(start, finish)).count
+        @relation.select(@column).public_send(mode).where(between_condition(start, finish)).send(@operation, *@operation_args)
       end
 
       private
 
+      def batch_size_for_mode_and_operation(mode, operation)
+        return DEFAULT_SUM_BATCH_SIZE if operation == :sum
+
+        mode == :distinct ? DEFAULT_DISTINCT_BATCH_SIZE : DEFAULT_BATCH_SIZE
+      end
+
       def between_condition(start, finish)
         return @column.between(start..(finish - 1)) if @column.is_a?(Arel::Attributes::Attribute)
 

spec/lib/gitlab/database/batch_count_spec.rb

@@ -13,11 +13,34 @@ RSpec.describe Gitlab::Database::BatchCount do
   let(:another_user) { create(:user) }
 
   before do
-    create_list(:issue, 3, author: user )
-    create_list(:issue, 2, author: another_user )
+    create_list(:issue, 3, author: user)
+    create_list(:issue, 2, author: another_user)
     allow(ActiveRecord::Base.connection).to receive(:transaction_open?).and_return(in_transaction)
   end
 
+  shared_examples 'disallowed configurations' do |method|
+    it 'returns fallback if start is bigger than finish' do
+      expect(described_class.public_send(method, *args, start: 1, finish: 0)).to eq(fallback)
+    end
+
+    it 'returns fallback if loops more than allowed' do
+      large_finish = Gitlab::Database::BatchCounter::MAX_ALLOWED_LOOPS * default_batch_size + 1
+      expect(described_class.public_send(method, *args, start: 1, finish: large_finish)).to eq(fallback)
+    end
+
+    it 'returns fallback if batch size is less than min required' do
+      expect(described_class.public_send(method, *args, batch_size: small_batch_size)).to eq(fallback)
+    end
+  end
+
+  shared_examples 'when a transaction is open' do
+    let(:in_transaction) { true }
+
+    it 'raises an error' do
+      expect { subject }.to raise_error('BatchCount can not be run inside a transaction')
+    end
+  end
+
   describe '#batch_count' do
     it 'counts table' do
       expect(described_class.batch_count(model)).to eq(5)
@@ -53,38 +76,32 @@ RSpec.describe Gitlab::Database::BatchCount do
       [1, 2, 4, 5, 6].each { |i| expect(described_class.batch_count(model, batch_size: i)).to eq(5) }
     end
 
-    it 'will raise an error if distinct count is requested' do
-      expect do
-        described_class.batch_count(model.distinct(column))
-      end.to raise_error 'Use distinct count for optimized distinct counting'
+    it 'counts with a start and finish' do
+      expect(described_class.batch_count(model, start: model.minimum(:id), finish: model.maximum(:id))).to eq(5)
     end
 
-    context 'in a transaction' do
-      let(:in_transaction) { true }
+    it "defaults the batch size to #{Gitlab::Database::BatchCounter::DEFAULT_BATCH_SIZE}" do
+      min_id = model.minimum(:id)
 
-      it 'cannot count' do
-        expect do
-          described_class.batch_count(model)
-        end.to raise_error 'BatchCount can not be run inside a transaction'
+      expect_next_instance_of(Gitlab::Database::BatchCounter) do |batch_counter|
+        expect(batch_counter).to receive(:batch_fetch).with(min_id, Gitlab::Database::BatchCounter::DEFAULT_BATCH_SIZE + min_id, :itself).once.and_call_original
       end
-    end
 
-    it 'counts with a start and finish' do
-      expect(described_class.batch_count(model, start: model.minimum(:id), finish: model.maximum(:id))).to eq(5)
+      described_class.batch_count(model)
     end
 
-    context 'disallowed configurations' do
-      it 'returns fallback if start is bigger than finish' do
-        expect(described_class.batch_count(model, start: 1, finish: 0)).to eq(fallback)
-      end
+    it_behaves_like 'when a transaction is open' do
+      subject { described_class.batch_count(model) }
+    end
 
-      it 'returns fallback if loops more than allowed' do
-        large_finish = Gitlab::Database::BatchCounter::MAX_ALLOWED_LOOPS * Gitlab::Database::BatchCounter::DEFAULT_BATCH_SIZE + 1
-        expect(described_class.batch_count(model, start: 1, finish: large_finish)).to eq(fallback)
+    context 'disallowed_configurations' do
+      include_examples 'disallowed configurations', :batch_count do
+        let(:args) { [Issue] }
+        let(:default_batch_size) { Gitlab::Database::BatchCounter::DEFAULT_BATCH_SIZE }
       end
 
-      it 'returns fallback if batch size is less than min required' do
-        expect(described_class.batch_count(model, batch_size: small_batch_size)).to eq(fallback)
+      it 'raises an error if distinct count is requested' do
+        expect { described_class.batch_count(model.distinct(column)) }.to raise_error 'Use distinct count for optimized distinct counting'
       end
     end
   end
@@ -128,18 +145,24 @@ RSpec.describe Gitlab::Database::BatchCount do
       expect(described_class.batch_distinct_count(model, column, start: User.minimum(:id), finish: User.maximum(:id))).to eq(2)
     end
 
-    context 'disallowed configurations' do
-      it 'returns fallback if start is bigger than finish' do
-        expect(described_class.batch_distinct_count(model, column, start: 1, finish: 0)).to eq(fallback)
-      end
+    it "defaults the batch size to #{Gitlab::Database::BatchCounter::DEFAULT_DISTINCT_BATCH_SIZE}" do
+      min_id = model.minimum(:id)
 
-      it 'returns fallback if loops more than allowed' do
-        large_finish = Gitlab::Database::BatchCounter::MAX_ALLOWED_LOOPS * Gitlab::Database::BatchCounter::DEFAULT_DISTINCT_BATCH_SIZE + 1
-        expect(described_class.batch_distinct_count(model, column, start: 1, finish: large_finish)).to eq(fallback)
+      expect_next_instance_of(Gitlab::Database::BatchCounter) do |batch_counter|
+        expect(batch_counter).to receive(:batch_fetch).with(min_id, Gitlab::Database::BatchCounter::DEFAULT_DISTINCT_BATCH_SIZE + min_id, :distinct).once.and_call_original
       end
 
-      it 'returns fallback if batch size is less than min required' do
-        expect(described_class.batch_distinct_count(model, column, batch_size: small_batch_size)).to eq(fallback)
+      described_class.batch_distinct_count(model)
+    end
+
+    it_behaves_like 'when a transaction is open' do
+      subject { described_class.batch_distinct_count(model, column) }
+    end
+
+    context 'disallowed configurations' do
+      include_examples 'disallowed configurations', :batch_distinct_count do
+        let(:args) { [model, column] }
+        let(:default_batch_size) { Gitlab::Database::BatchCounter::DEFAULT_DISTINCT_BATCH_SIZE }
       end
 
       it 'will raise an error if distinct count with the :id column is requested' do
@@ -149,4 +172,55 @@ RSpec.describe Gitlab::Database::BatchCount do
       end
     end
   end
+
+  describe '#batch_sum' do
+    let(:column) { :weight }
+
+    before do
+      Issue.first.update_attribute(column, 3)
+      Issue.last.update_attribute(column, 4)
+    end
+
+    it 'returns the sum of values in the given column' do
+      expect(described_class.batch_sum(model, column)).to eq(7)
+    end
+
+    it 'works when given an Arel column' do
+      expect(described_class.batch_sum(model, model.arel_table[column])).to eq(7)
+    end
+
+    it 'works with a batch size of 50K' do
+      expect(described_class.batch_sum(model, column, batch_size: 50_000)).to eq(7)
+    end
+
+    it 'works with start and finish provided' do
+      expect(described_class.batch_sum(model, column, start: model.minimum(:id), finish: model.maximum(:id))).to eq(7)
+    end
+
+    it 'returns the same result regardless of batch size' do
+      stub_const('Gitlab::Database::BatchCounter::DEFAULT_SUM_BATCH_SIZE', 0)
+
+      (1..(model.count + 1)).each { |i| expect(described_class.batch_sum(model, column, batch_size: i)).to eq(7) }
+    end
+
+    it "defaults the batch size to #{Gitlab::Database::BatchCounter::DEFAULT_SUM_BATCH_SIZE}" do
+      min_id = model.minimum(:id)
+
+      expect_next_instance_of(Gitlab::Database::BatchCounter) do |batch_counter|
+        expect(batch_counter).to receive(:batch_fetch).with(min_id, Gitlab::Database::BatchCounter::DEFAULT_SUM_BATCH_SIZE + min_id, :itself).once.and_call_original
+      end
+
+      described_class.batch_sum(model, column)
+    end
+
+    it_behaves_like 'when a transaction is open' do
+      subject { described_class.batch_sum(model, column) }
+    end
+
+    it_behaves_like 'disallowed configurations', :batch_sum do
+      let(:args) { [model, column] }
+      let(:default_batch_size) { Gitlab::Database::BatchCounter::DEFAULT_SUM_BATCH_SIZE }
+      let(:small_batch_size) { Gitlab::Database::BatchCounter::DEFAULT_SUM_BATCH_SIZE - 1 }
+    end
+  end
 end