Drop NULL constraint on Geo event columns

The columns effected store the repository storage path, which can't be
NULL. So in general the path can't be NULL. However, the tables also
include the shard name. From the shard name, the storage path can be
determined, allowing for a more dynamic approach.

db/schema.rb

@@ -1020,7 +1020,7 @@ ActiveRecord::Schema.define(version: 20180419031622) do
   create_table "geo_hashed_storage_migrated_events", id: :bigserial, force: :cascade do |t|
     t.integer "project_id", null: false
     t.text "repository_storage_name", null: false
-    t.text "repository_storage_path", null: false
+    t.text "repository_storage_path"
     t.text "old_disk_path", null: false
     t.text "new_disk_path", null: false
     t.text "old_wiki_disk_path", null: false
@@ -1126,7 +1126,7 @@ ActiveRecord::Schema.define(version: 20180419031622) do
   create_table "geo_repository_created_events", id: :bigserial, force: :cascade do |t|
     t.integer "project_id", null: false
     t.text "repository_storage_name", null: false
-    t.text "repository_storage_path", null: false
+    t.text "repository_storage_path"
     t.text "repo_path", null: false
     t.text "wiki_path"
     t.text "project_name", null: false
@@ -1137,7 +1137,7 @@ ActiveRecord::Schema.define(version: 20180419031622) do
   create_table "geo_repository_deleted_events", id: :bigserial, force: :cascade do |t|
     t.integer "project_id", null: false
     t.text "repository_storage_name", null: false
-    t.text "repository_storage_path", null: false
+    t.text "repository_storage_path"
     t.text "deleted_path", null: false
     t.text "deleted_wiki_path"
     t.text "deleted_project_name", null: false
@@ -1148,7 +1148,7 @@ ActiveRecord::Schema.define(version: 20180419031622) do
   create_table "geo_repository_renamed_events", id: :bigserial, force: :cascade do |t|
     t.integer "project_id", null: false
     t.text "repository_storage_name", null: false
-    t.text "repository_storage_path", null: false
+    t.text "repository_storage_path"
     t.text "old_path_with_namespace", null: false
     t.text "new_path_with_namespace", null: false
     t.text "old_wiki_path_with_namespace", null: false

ee/db/migrate/20180416112831_drop_null_constraint_geo_events_storage_path.rb

+class DropNullConstraintGeoEventsStoragePath < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+  TABLES = %i(geo_hashed_storage_migrated_events geo_repository_created_events
+              geo_repository_deleted_events geo_repository_renamed_events)
+
+  def up 
+    TABLES.each do |table|
+      change_column_null(table, :repository_storage_path, true)
+    end
+  end
+
+  def down
+    TABLES.each do |table|
+      change_column_null(table, :repository_storage_path, false)
+    end
+  end
+end