Migrate MR commits and diffs to new tablesmerge-request-commits-table

Previously, we stored these as serialised fields - `st_{commits,diffs}` - on the
`merge_request_diffs` table. These now have their own tables -
`merge_request_diff_{commits,diffs}` - with a column for each attribute of the
serialised data.

Add a background migration to go through the existing MR diffs and migrate them
to the new format. Ignore any contents that cannot be displayed.

2 files changed, 25 insertions, 1 deletions

diff --git a/db/post_migrate/20170703130158_schedule_merge_request_diff_migrations.rb b/db/post_migrate/20170703130158_schedule_merge_request_diff_migrations.rb
new file mode 100644
index 00000000000..ae53e3e1ab3
--- /dev/null
+++ b/db/post_migrate/20170703130158_schedule_merge_request_diff_migrations.rb
@@ -0,0 +1,24 @@
+class ScheduleMergeRequestDiffMigrations < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  class MergeRequestDiff < ActiveRecord::Base
+    self.table_name = 'merge_request_diffs'
+  end
+
+  def up
+    MergeRequestDiff.all.in_batches do |relation|
+      jobs = relation.pluck(:id).map do |id|
+        ['DeserializeMergeRequestDiffsAndCommits', [id]]
+      end
+
+      BackgroundMigrationWorker.perform_bulk(*jobs)
+    end
+  end
+
+  def down
+  end
+end
diff --git a/db/schema.rb b/db/schema.rb
index 4937f290d3e..b51e4942750 100644
--- a/db/schema.rb
+++ b/db/schema.rb
@@ -11,7 +11,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 20170623080805) do
+ActiveRecord::Schema.define(version: 20170703130158) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"