Change commit_id type on commit_user_mentions table

Change commit_id column type from binary to string.

changelogs/unreleased/42738-change-commit-user-mentions-commit-id-column-type.yml

+---
+title: Change commit_id type on commit_user_mentions table
+merge_request: 21651
+author:
+type: fixed

db/migrate/20191212140117_change_commit_user_mentions_commit_id_column_type.rb

+# frozen_string_literal: true
+
+class ChangeCommitUserMentionsCommitIdColumnType < ActiveRecord::Migration[5.2]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  OLD_INDEX = 'commit_user_mentions_on_commit_id_and_note_id_index'
+  OLD_TMP_INDEX = 'temp_commit_id_and_note_id_index'
+  NEW_TMP_INDEX = 'temp_commit_id_for_type_change_and_note_id_index'
+  NEW_INDEX = 'commit_id_and_note_id_index'
+
+  def up
+    # the initial index name is too long and fails during migration. Renaming the index first.
+    add_concurrent_index :commit_user_mentions, [:commit_id, :note_id], name: OLD_TMP_INDEX
+    remove_concurrent_index_by_name :commit_user_mentions, OLD_INDEX
+
+    change_column_type_concurrently :commit_user_mentions, :commit_id, :string
+
+    # change_column_type_concurrently creates a new index for new column `commit_id_for_type` based on existing
+    # `temp_commit_id_and_note_id_index` naming it `temp_commit_id_for_type_change_and_note_id_index`, yet keeping
+    # `temp_commit_id_and_note_id_index` for `commit_id`, that will be cleaned
+    # by `cleanup_concurrent_column_type_change :commit_user_mentions, :commit_id` in a later migration.
+    #
+    # So we'll rename `temp_commit_id_for_type_change_and_note_id_index` to initialy intended name: `commit_id_and_note_id_index`.
+
+    add_concurrent_index :commit_user_mentions, [:commit_id_for_type_change, :note_id], name: NEW_INDEX
+    remove_concurrent_index_by_name :commit_user_mentions, NEW_TMP_INDEX
+  end
+
+  def down
+    cleanup_concurrent_column_type_change :commit_user_mentions, :commit_id
+  end
+end

db/post_migrate/20191212162434_change_commit_user_mentions_commit_id_column_type_cleanup.rb

+# frozen_string_literal: true
+
+class ChangeCommitUserMentionsCommitIdColumnTypeCleanup < ActiveRecord::Migration[5.2]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  NEW_INDEX = 'commit_id_for_type_change_and_note_id_index'
+  OLD_INDEX = 'commit_user_mentions_on_commit_id_and_note_id_index'
+
+  def up
+    cleanup_concurrent_column_type_change :commit_user_mentions, :commit_id
+  end
+
+  def down
+    change_column_type_concurrently :commit_user_mentions, :commit_id, :binary
+
+    # change_column_type_concurrently creates a new index based on existing commit_id_and_note_id_index` naming it
+    # `commit_id_for_type_change_and_note_id_index` so we'll rename it back to its original name.
+    add_concurrent_index :commit_user_mentions, [:commit_id_for_type_change, :note_id], name: OLD_INDEX
+    remove_concurrent_index_by_name :commit_user_mentions, NEW_INDEX
+  end
+end

db/schema.rb

@@ -1217,11 +1217,11 @@ ActiveRecord::Schema.define(version: 2019_12_14_175727) do
 
   create_table "commit_user_mentions", force: :cascade do |t|
     t.integer "note_id", null: false
-    t.binary "commit_id", null: false
     t.integer "mentioned_users_ids", array: true
     t.integer "mentioned_projects_ids", array: true
     t.integer "mentioned_groups_ids", array: true
-    t.index ["commit_id", "note_id"], name: "commit_user_mentions_on_commit_id_and_note_id_index"
+    t.string "commit_id", null: false
+    t.index ["commit_id", "note_id"], name: "commit_id_and_note_id_index"
     t.index ["note_id"], name: "index_commit_user_mentions_on_note_id", unique: true
   end