Reset merge status from mergeable MRs

Adds migrations to reset the merge_status of opened,
mergeable MRs. That's required by
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/28513
so we're able to sync the status update along merge-ref,
without leaving MRs with a stale merge-ref.

3 files changed, 53 insertions, 1 deletions

diff --git a/db/migrate/20190530154715_add_index_to_merge_requests_state_and_merge_status.rb b/db/migrate/20190530154715_add_index_to_merge_requests_state_and_merge_status.rb
new file mode 100644
index 00000000000..e669f81ca35
--- /dev/null
+++ b/db/migrate/20190530154715_add_index_to_merge_requests_state_and_merge_status.rb
@@ -0,0 +1,21 @@
+# frozen_string_literal: true
+
+# See http://doc.gitlab.com/ce/development/migration_style_guide.html
+# for more information on how to write migrations for GitLab.
+
+class AddIndexToMergeRequestsStateAndMergeStatus < ActiveRecord::Migration[5.1]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  def up
+    add_concurrent_index :merge_requests, [:state, :merge_status],
+                         where: "state = 'opened' AND merge_status = 'can_be_merged'"
+  end
+
+  def down
+    remove_concurrent_index :merge_requests, [:state, :merge_status]
+  end
+end
diff --git a/db/post_migrate/20190528180441_enqueue_reset_merge_status.rb b/db/post_migrate/20190528180441_enqueue_reset_merge_status.rb
new file mode 100644
index 00000000000..1b668d85bac
--- /dev/null
+++ b/db/post_migrate/20190528180441_enqueue_reset_merge_status.rb
@@ -0,0 +1,30 @@
+# frozen_string_literal: true
+
+# See http://doc.gitlab.com/ce/development/migration_style_guide.html
+# for more information on how to write migrations for GitLab.
+
+class EnqueueResetMergeStatus < ActiveRecord::Migration[5.1]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+  BATCH_SIZE = 10_000
+  MIGRATION = 'ResetMergeStatus'
+  DELAY_INTERVAL = 5.minutes.to_i
+
+  disable_ddl_transaction!
+
+  def up
+    say 'Scheduling `ResetMergeStatus` jobs'
+
+    # We currently have around 135_000 opened, mergeable MRs in GitLab.com. This iteration
+    # will schedule around 13 batches of 10_000 MRs, which should take around 1 hour to
+    # complete.
+    relation = MergeRequest.where(state: 'opened', merge_status: 'can_be_merged')
+
+    relation.each_batch(of: BATCH_SIZE) do |batch, index|
+      range = batch.pluck('MIN(id)', 'MAX(id)').first
+
+      BackgroundMigrationWorker.perform_in(index * DELAY_INTERVAL, MIGRATION, range)
+    end
+  end
+end
diff --git a/db/schema.rb b/db/schema.rb
index 89140048ad3..dc73f7f02da 100644
--- a/db/schema.rb
+++ b/db/schema.rb
@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 20190527194900) do
+ActiveRecord::Schema.define(version: 20190530154715) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -1361,6 +1361,7 @@ ActiveRecord::Schema.define(version: 20190527194900) do
     t.index ["source_branch"], name: "index_merge_requests_on_source_branch", using: :btree
     t.index ["source_project_id", "source_branch"], name: "index_merge_requests_on_source_project_and_branch_state_opened", where: "((state)::text = 'opened'::text)", using: :btree
     t.index ["source_project_id", "source_branch"], name: "index_merge_requests_on_source_project_id_and_source_branch", using: :btree
+    t.index ["state", "merge_status"], name: "index_merge_requests_on_state_and_merge_status", where: "(((state)::text = 'opened'::text) AND ((merge_status)::text = 'can_be_merged'::text))", using: :btree
     t.index ["target_branch"], name: "index_merge_requests_on_target_branch", using: :btree
     t.index ["target_project_id", "iid"], name: "index_merge_requests_on_target_project_id_and_iid", unique: true, using: :btree
     t.index ["target_project_id", "iid"], name: "index_merge_requests_on_target_project_id_and_iid_opened", where: "((state)::text = 'opened'::text)", using: :btree