Decrease memory use and increase performance of Google Code importer.

lib/gitlab/google_code_import/importer.rb

@@ -62,24 +62,7 @@ module Gitlab
       def import_issues
         return unless repo.issues
 
-        last_id = 0
-
-        deleted_issues = []
-
-        repo.issues.each do |raw_issue|
-          while raw_issue["id"] > last_id + 1
-            last_id += 1
-
-            issue = project.issues.create!(
-              title:        "Deleted issue",
-              description:  "*This issue has been deleted*",
-              author_id:    project.creator_id,
-              state:        "closed"
-            )
-            deleted_issues << issue
-          end
-          last_id = raw_issue["id"]
-
+        while raw_issue = repo.issues.shift
           author  = user_map[raw_issue["author"]["name"]]
           date    = DateTime.parse(raw_issue["published"]).to_formatted_s(:long)
 
@@ -116,7 +99,8 @@ module Gitlab
             end
           end
 
-          issue = project.issues.create!(
+          issue = Issue.create!(
+            project_id:   project.id,
             title:        raw_issue["title"],
             description:  body,
             author_id:    project.creator_id,
@@ -125,14 +109,17 @@ module Gitlab
           )
           issue.add_labels_by_names(labels)
 
-          import_issue_comments(issue, comments)
+          if issue.iid != raw_issue["id"]
+            issue.update_attribute(:iid, raw_issue["id"])
           end
 
-        deleted_issues.each(&:destroy!)
+          import_issue_comments(issue, comments)
+        end
       end
 
       def import_issue_comments(issue, comments)
-        comments.each do |raw_comment|
+        Note.transaction do
+          while raw_comment = comments.shift
             next if raw_comment.has_key?("deletedBy")
 
             content     = format_content(raw_comment["content"])
@@ -153,13 +140,17 @@ module Gitlab
               attachments
             )
 
-          issue.notes.create!(
+            # Needs to match order of `comment_columns` below.
+            Note.create!(
               project_id:     project.id,
+              noteable_type:  "Issue",
+              noteable_id:    issue.id,
               author_id:      project.creator_id,
               note:           body
             )
           end
         end
+      end
 
       def nice_label_color(name)
         case name
@@ -236,7 +227,7 @@ module Gitlab
 
       def create_label(name)
         color = nice_label_color(name)
-        project.labels.create!(name: name, color: color)
+        Label.create!(project_id: project.id, name: name, color: color)
       end
 
       def format_content(raw_content)