Use SQL to find the gap instead of iterating

Also removes unnecessary methods causing extra queries

2 files changed, 26 insertions, 2 deletions

diff --git a/db/migrate/20190802012622_reorder_issues_project_id_relative_position_index.rb b/db/migrate/20190802012622_reorder_issues_project_id_relative_position_index.rb
new file mode 100644
index 00000000000..12088dd763f
--- /dev/null
+++ b/db/migrate/20190802012622_reorder_issues_project_id_relative_position_index.rb
@@ -0,0 +1,24 @@
+# frozen_string_literal: true
+
+class ReorderIssuesProjectIdRelativePositionIndex < ActiveRecord::Migration[5.2]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  OLD_INDEX_NAME = 'index_issues_on_project_id_and_state_and_rel_position_and_id'
+  NEW_INDEX_NAME = 'index_issues_on_project_id_and_rel_position_and_state_and_id'
+
+  def up
+    add_concurrent_index :issues, [:project_id, :relative_position, :state, :id], order: { id: :desc }, name: NEW_INDEX_NAME
+
+    remove_concurrent_index_by_name :issues, OLD_INDEX_NAME
+  end
+
+  def down
+    add_concurrent_index :issues, [:project_id, :state, :relative_position, :id], order: { id: :desc }, name: OLD_INDEX_NAME
+
+    remove_concurrent_index_by_name :issues, NEW_INDEX_NAME
+  end
+end
diff --git a/db/schema.rb b/db/schema.rb
index fe3fa597006..a9b7c1930e3 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: 2019_08_01_114109) do
+ActiveRecord::Schema.define(version: 2019_08_02_012622) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "pg_trgm"
@@ -1716,7 +1716,7 @@ ActiveRecord::Schema.define(version: 2019_08_01_114109) do
     t.index ["project_id", "created_at", "id", "state"], name: "index_issues_on_project_id_and_created_at_and_id_and_state"
     t.index ["project_id", "due_date", "id", "state"], name: "idx_issues_on_project_id_and_due_date_and_id_and_state_partial", where: "(due_date IS NOT NULL)"
     t.index ["project_id", "iid"], name: "index_issues_on_project_id_and_iid", unique: true
-    t.index ["project_id", "state", "relative_position", "id"], name: "index_issues_on_project_id_and_state_and_rel_position_and_id", order: { id: :desc }
+    t.index ["project_id", "relative_position", "state", "id"], name: "index_issues_on_project_id_and_rel_position_and_state_and_id", order: { id: :desc }
     t.index ["project_id", "updated_at", "id", "state"], name: "index_issues_on_project_id_and_updated_at_and_id_and_state"
     t.index ["relative_position"], name: "index_issues_on_relative_position"
     t.index ["state"], name: "index_issues_on_state"