Improve performance of public snippets API endpoint

changelogs/unreleased/ap-35389-api-snippets-public-personal.yml

+---
+title: Improve performance of /api/:version/snippets/public API and only return public
+  personal snippets
+merge_request: 20339
+author:
+type: performance

db/migrate/20191119023952_add_created_at_index_to_snippets.rb

+# frozen_string_literal: true
+
+class AddCreatedAtIndexToSnippets < ActiveRecord::Migration[5.2]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  def up
+    add_concurrent_index :snippets, :created_at
+  end
+
+  def down
+    remove_concurrent_index :snippets, :created_at
+  end
+end

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_11_18_182722) do
+ActiveRecord::Schema.define(version: 2019_11_19_023952) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "pg_trgm"
@@ -3628,6 +3628,7 @@ ActiveRecord::Schema.define(version: 2019_11_18_182722) do
     t.boolean "secret", default: false, null: false
     t.index ["author_id"], name: "index_snippets_on_author_id"
     t.index ["content"], name: "index_snippets_on_content_trigram", opclass: :gin_trgm_ops, using: :gin
+    t.index ["created_at"], name: "index_snippets_on_created_at"
     t.index ["file_name"], name: "index_snippets_on_file_name_trigram", opclass: :gin_trgm_ops, using: :gin
     t.index ["project_id", "visibility_level"], name: "index_snippets_on_project_id_and_visibility_level"
     t.index ["title"], name: "index_snippets_on_title_trigram", opclass: :gin_trgm_ops, using: :gin

lib/api/snippets.rb

@@ -14,7 +14,7 @@ module API
         end
 
         def public_snippets
-          SnippetsFinder.new(current_user, scope: :are_public).execute
+          Snippet.only_personal_snippets.are_public.fresh
         end
 
         def snippets
@@ -33,7 +33,7 @@ module API
         present paginate(snippets_for_current_user), with: Entities::PersonalSnippet
       end
 
-      desc 'List all public snippets current_user has access to' do
+      desc 'List all public personal snippets current_user has access to' do
         detail 'This feature was introduced in GitLab 8.15.'
         success Entities::PersonalSnippet
       end

spec/requests/api/snippets_spec.rb

@@ -66,6 +66,9 @@ describe API::Snippets do
     let!(:public_snippet_other) { create(:personal_snippet, :public, author: other_user) }
     let!(:private_snippet_other) { create(:personal_snippet, :private, author: other_user) }
     let!(:internal_snippet_other) { create(:personal_snippet, :internal, author: other_user) }
+    let!(:public_snippet_project) { create(:project_snippet, :public, author: user) }
+    let!(:private_snippet_project) { create(:project_snippet, :private, author: user) }
+    let!(:internal_snippet_project) { create(:project_snippet, :internal, author: user) }
 
     it 'returns all snippets with public visibility from all users' do
       get api("/snippets/public", user)
@@ -76,10 +79,10 @@ describe API::Snippets do
       expect(json_response.map { |snippet| snippet['id']} ).to contain_exactly(
         public_snippet.id,
         public_snippet_other.id)
-      expect(json_response.map { |snippet| snippet['web_url']} ).to include(
+      expect(json_response.map { |snippet| snippet['web_url']} ).to contain_exactly(
         "http://localhost/snippets/#{public_snippet.id}",
         "http://localhost/snippets/#{public_snippet_other.id}")
-      expect(json_response.map { |snippet| snippet['raw_url']} ).to include(
+      expect(json_response.map { |snippet| snippet['raw_url']} ).to contain_exactly(
         "http://localhost/snippets/#{public_snippet.id}/raw",
         "http://localhost/snippets/#{public_snippet_other.id}/raw")
     end