Support batch record collections

README.md

@@ -111,6 +111,41 @@ end
 title,content
 My Title,Hello World!
 ```
+### Processing Batch Collections
+
+The Maintenance Tasks gem supports processing Active Records in batches. This
+can reduce the number of calls your Task makes to the database. Use `in_batches`
+to specify that your Task should process records in batches. The default batch
+size is 100, but a custom size can be specified.
+
+```ruby
+# app/tasks/maintenance/update_posts_in_batches_task.rb
+module Maintenance
+  class UpdatePostsInBatchesTask < MaintenanceTasks::Task
+    in_batches 50
+
+    def collection
+      Post.all
+    end
+
+    def count
+      collection.count
+    end
+
+    def process(batch_of_posts)
+      Post.where(id: batch_of_posts.map(&:id)).update_all(
+        content: "New content added on #{Time.now.utc}"
+      )    
+    end
+  end
+end
+```
+
+Ensure that you've implemented the following methods:
+* `collection`: return an Active Record Relation to be iterated over.
+* `process`: do the work of your Task on a _batch_ of records.
+* `count`: return the number of rows that will be iterated over (this should
+still be the number of records to be processed, not the number of batches).
 
 ### Considerations when writing Tasks
 

app/jobs/maintenance_tasks/task_job.rb

@@ -31,7 +31,18 @@ def build_enumerator(_run, cursor:)
 
       case collection
       when ActiveRecord::Relation
-        enumerator_builder.active_record_on_records(collection, cursor: cursor)
+        if @task.in_batches?
+          enumerator_builder.active_record_on_batches(
+            collection,
+            cursor: cursor,
+            batch_size: @task.batch_size
+          )
+        else
+          enumerator_builder.active_record_on_records(
+            collection,
+            cursor: cursor
+          )
+        end
       when Array
         enumerator_builder.build_array_enumerator(collection, cursor: cursor)
       when CSV
@@ -50,7 +61,8 @@ def build_enumerator(_run, cursor:)
     def each_iteration(input, _run)
       throw(:abort, :skip_complete_callbacks) if @run.stopping?
       task_iteration(input)
-      @ticker.tick
+      batch_size = @task.in_batches? ? input.size : 1
+      @ticker.tick(batch_size)
       @run.reload_status
     end
 

app/models/maintenance_tasks/ticker.rb

@@ -28,11 +28,11 @@ def initialize(throttle_duration, &persist)
       @ticks_recorded = 0
     end
 
-    # Increments the tick count by one, and may persist the new value if the
-    # threshold duration has passed since initialization or the tick count was
-    # last persisted.
-    def tick
-      @ticks_recorded += 1
+    # Increments the tick count, which defaults to one. It may persist the new
+    # value if the threshold duration has passed since initialization or the
+    # tick count was last persisted.
+    def tick(increment = 1)
+      @ticks_recorded += increment
       persist if persist?
     end
 

app/tasks/maintenance_tasks/task.rb

@@ -8,6 +8,8 @@ class Task
     class NotFoundError < NameError; end
 
     class << self
+      attr_reader :batch_size
+
       # Finds a Task with the given name.
       #
       # @param name [String] the name of the Task to be found.
@@ -72,6 +74,14 @@ def count
         new.count
       end
 
+      # Make this a Task that processes batches.
+      #
+      # @param batch_size [Integer] optionally, a custom batch size can be
+      #   specified. Defaults to 100 if one is not provided.
+      def in_batches(batch_size = 100)
+        @batch_size = batch_size
+      end
+
       private
 
       def load_constants
@@ -110,5 +120,20 @@ def process(_item)
     # @return [Integer, nil]
     def count
     end
+
+    # The batch size for this Task instance, if any.
+    #
+    # @return [Integer, nil] the batch size for this Task instance, or nil if
+    #   the Task does not process batches.
+    def batch_size
+      self.class.batch_size
+    end
+
+    # Whether this Task instance processes batches.
+    #
+    # @return [Boolean] whether this Task instance processes batches.
+    def in_batches?
+      batch_size.present?
+    end
   end
 end

test/dummy/app/tasks/maintenance/update_posts_in_batches_task.rb

@@ -0,0 +1,20 @@
+# frozen_string_literal: true
+module Maintenance
+  class UpdatePostsInBatchesTask < MaintenanceTasks::Task
+    in_batches 5
+
+    def collection
+      Post.all
+    end
+
+    def count
+      collection.count
+    end
+
+    def process(batch_of_posts)
+      Post.where(id: batch_of_posts.map(&:id)).update_all(
+        content: "New content added on #{Time.now.utc}"
+      )
+    end
+  end
+end

test/jobs/maintenance_tasks/task_job_test.rb

@@ -337,5 +337,18 @@ class << self
     ensure
       MaintenanceTasks.error_handler = error_handler_before
     end
+
+    test ".perform_now handles batched tasks" do
+      5.times do |i|
+        Post.create!(title: "Another Post ##{i}", content: "Content ##{i}")
+      end
+      # We expect 2 batches (7 posts => 5 + 2)
+      Maintenance::UpdatePostsInBatchesTask.any_instance.expects(:process).twice
+
+      run = Run.create!(task_name: "Maintenance::UpdatePostsInBatchesTask")
+      TaskJob.perform_now(run)
+
+      assert_equal Post.count, run.reload.tick_count
+    end
   end
 end

test/models/maintenance_tasks/task_data_test.rb

@@ -26,6 +26,7 @@ class TaskDataTest < ActiveSupport::TestCase
         "Maintenance::ErrorTask",
         "Maintenance::ImportPostsTask",
         "Maintenance::TestTask",
+        "Maintenance::UpdatePostsInBatchesTask",
         "Maintenance::UpdatePostsTask",
       ]
       assert_equal expected, TaskData.available_tasks.map(&:name)

test/system/maintenance_tasks/tasks_test.rb

@@ -23,6 +23,7 @@ class TasksTest < ApplicationSystemTestCase
         "Maintenance::ErrorTask\nNew",
         "Maintenance::ImportPostsTask\nNew",
         "Maintenance::TestTask\nNew",
+        "Maintenance::UpdatePostsInBatchesTask\nNew",
         "Completed Tasks",
         "Maintenance::UpdatePostsTask\nSucceeded",
       ]

test/tasks/maintenance_tasks/task_test.rb

@@ -10,6 +10,7 @@ class TaskTest < ActiveSupport::TestCase
         "Maintenance::ErrorTask",
         "Maintenance::ImportPostsTask",
         "Maintenance::TestTask",
+        "Maintenance::UpdatePostsInBatchesTask",
         "Maintenance::UpdatePostsTask",
       ]
       assert_equal expected,