Improve migration robustness and speed.

db/migrate/20180223120443_create_user_contributed_projects_table.rb

@@ -9,8 +9,6 @@ class CreateUserContributedProjectsTable < ActiveRecord::Migration
     create_table :user_contributed_projects, id: false do |t|
       t.references :user, null: false
       t.references :project, null: false
-
-      t.index [:user_id, :project_id], unique: true
     end
 
     add_concurrent_foreign_key :user_contributed_projects, :users, column: :user_id, on_delete: :cascade

db/post_migrate/20180223124427_build_user_contributed_projects_table.rb

@@ -12,10 +12,14 @@ class BuildUserContributedProjectsTable < ActiveRecord::Migration
     else
       MysqlStrategy.new
     end.up
+
+    add_concurrent_index :user_contributed_projects, [:project_id, :user_id], unique: true
   end
 
   def down
     execute "TRUNCATE user_contributed_projects"
+
+    remove_concurrent_index_by_name :user_contributed_projects, 'index_user_contributed_projects_on_project_id_and_user_id'
   end
 
   private
@@ -24,7 +28,7 @@ class BuildUserContributedProjectsTable < ActiveRecord::Migration
     include Gitlab::Database::MigrationHelpers
 
     BATCH_SIZE = 100_000
-    SLEEP_TIME = 30
+    SLEEP_TIME = 5
 
     def up
       with_index(:events, [:author_id, :project_id], name: 'events_user_contributions_temp', where: 'project_id IS NOT NULL') do
@@ -44,10 +48,14 @@ class BuildUserContributedProjectsTable < ActiveRecord::Migration
           records += result.cmd_tuples
           Rails.logger.info "Building user_contributed_projects table, batch ##{iteration} complete, created #{records} overall"
           Kernel.sleep(SLEEP_TIME) if result.cmd_tuples > 0
+        rescue ActiveRecord::InvalidForeignKey => e
+          Rails.logger.info "Retry on InvalidForeignKey: #{e}"
+          retry
         end while result.cmd_tuples > 0
       end
 
       execute "ANALYZE user_contributed_projects"
+
     end
 
     private

db/schema.rb

@@ -1820,7 +1820,7 @@ ActiveRecord::Schema.define(version: 20180304204842) do
     t.integer "project_id", null: false
   end
 
-  add_index "user_contributed_projects", ["user_id", "project_id"], name: "index_user_contributed_projects_on_user_id_and_project_id", unique: true, using: :btree
+  add_index "user_contributed_projects", ["project_id", "user_id"], name: "index_user_contributed_projects_on_project_id_and_user_id", unique: true, using: :btree
 
   create_table "user_custom_attributes", force: :cascade do |t|
     t.datetime_with_timezone "created_at", null: false