Use EachBatch concern to loop over batches

app/workers/namespaceless_project_destroy_worker.rb

@@ -19,7 +19,7 @@ class NamespacelessProjectDestroyWorker
       return
     end
 
-    return if namespace?(project)  # Reject doing anything for projects that *do* have a namespace
+    return if project.namespace  # Reject doing anything for projects that *do* have a namespace
 
     project.team.truncate
 
@@ -30,10 +30,6 @@ class NamespacelessProjectDestroyWorker
 
   private
 
-  def namespace?(project)
-    project.namespace_id && Namespace.exists?(project.namespace_id)
-  end
-
   def unlink_fork(project)
     merge_requests = project.forked_from_project.merge_requests.opened.from_project(project)
 

db/post_migrate/20170816102555_cleanup_nonexisting_namespace_pending_delete_projects.rb

@@ -8,35 +8,31 @@ class CleanupNonexistingNamespacePendingDeleteProjects < ActiveRecord::Migration
 
   disable_ddl_transaction!
 
-  def up
-    @offset = 0
+  class Project < ActiveRecord::Base
+    self.table_name = 'projects'
 
-    loop do
-      ids = pending_delete_batch
+    include ::EachBatch
+  end
 
-      break if ids.empty?
+  class Namespace < ActiveRecord::Base
+    self.table_name = 'namespaces'
+  end
 
-      args = ids.map { |id| Array(id) }
+  def up
+    find_projects.each_batch do |batch|
+      args = batch.pluck(:id).map { |id| [id] }
 
       NamespacelessProjectDestroyWorker.bulk_perform_async(args)
-
-      @offset += 1
     end
   end
 
   def down
-    # noop
+    # NOOP
   end
 
   private
 
-  def pending_delete_batch
-    connection.exec_query(find_batch).map { |row| row['id'].to_i }
-  end
-
-  BATCH_SIZE = 5000
-
-  def find_batch
+  def find_projects
     projects = Project.arel_table
     namespaces = Namespace.arel_table
 
@@ -44,11 +40,15 @@ class CleanupNonexistingNamespacePendingDeleteProjects < ActiveRecord::Migration
                         .where(namespaces[:id].eq(projects[:namespace_id]))
                         .exists.not
 
-    projects.project(projects[:id])
-      .where(projects[:pending_delete].eq(true))
+    # SELECT "projects"."id"
+    # FROM "projects"
+    # WHERE "projects"."pending_delete" = 't'
+    #   AND (NOT (EXISTS
+    #               (SELECT 1
+    #                FROM "namespaces"
+    #                WHERE "namespaces"."id" = "projects"."namespace_id")))
+    Project.where(projects[:pending_delete].eq(true))
       .where(namespace_query)
-      .skip(@offset * BATCH_SIZE)
-      .take(BATCH_SIZE)
-      .to_sql
+      .select(:id)
   end
 end