Remove the project_authorizations.id column

This column used to be a 32 bits integer, allowing for only a maximum of
2 147 483 647 rows. Given enough users one can hit this limit pretty
quickly, as was the case for GitLab.com.

Changing this type to bigint (= 64 bits) would give us more space, but
we'd eventually hit the same limit given enough users and projects. A
much more sustainable solution is to simply drop the "id" column.

There were only 2 lines of code depending on this column being present,
and neither truly required it to be present. Instead the code now uses
the "project_id" column combined with the "user_id" column. This means
that instead of something like this:

    DELETE FROM project_authorizations
    WHERE user_id = X
    AND id = Y;

We now run the following when removing rows:

    DELETE FROM project_authorizations
    WHERE user_id = X
    AND project_id = Y;

Since both user_id and project_id are indexed this should not slow down
the DELETE query.

This commit also removes the "dependent: destroy" clause from the
"project_authorizations" relation in the User and Project models.
Keeping this prevents Rails from being able to remove data as it relies
on an "id" column being present. Since the "project_authorizations"
table has proper foreign keys set up (with cascading removals) we don't
need to depend on any Rails logic.

2 files changed, 15 insertions, 3 deletions

diff --git a/db/post_migrate/20170106172224_remove_project_authorizations_id_column.rb b/db/post_migrate/20170106172224_remove_project_authorizations_id_column.rb
new file mode 100644
index 00000000000..7c788160022
--- /dev/null
+++ b/db/post_migrate/20170106172224_remove_project_authorizations_id_column.rb
@@ -0,0 +1,12 @@
+# See http://doc.gitlab.com/ce/development/migration_style_guide.html
+# for more information on how to write migrations for GitLab.
+
+class RemoveProjectAuthorizationsIdColumn < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  def change
+    remove_column :project_authorizations, :id, :primary_key
+  end
+end
diff --git a/db/schema.rb b/db/schema.rb
index 923ece86edb..379e566e9ec 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: 20161227192806) do
+ActiveRecord::Schema.define(version: 20170106172224) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -861,7 +861,7 @@ ActiveRecord::Schema.define(version: 20161227192806) do
   add_index "personal_access_tokens", ["token"], name: "index_personal_access_tokens_on_token", unique: true, using: :btree
   add_index "personal_access_tokens", ["user_id"], name: "index_personal_access_tokens_on_user_id", using: :btree
 
-  create_table "project_authorizations", force: :cascade do |t|
+  create_table "project_authorizations", id: false, force: :cascade do |t|
     t.integer "user_id"
     t.integer "project_id"
     t.integer "access_level"
@@ -1306,4 +1306,4 @@ ActiveRecord::Schema.define(version: 20161227192806) do
   add_foreign_key "subscriptions", "projects", on_delete: :cascade
   add_foreign_key "trending_projects", "projects", on_delete: :cascade
   add_foreign_key "u2f_registrations", "users"
-end
\ No newline at end of file
+end