Add Migration to Index members on user_id, source_id, and source_type

changelogs/unreleased/index-members-user-id-source-id-source-type.yml

+---
+title: Add migration to index members on user_id, source_id, and source_type
+merge_request: 59051
+author:
+type: performance

db/post_migrate/20210409185501_index_members_on_user_id_source_id_source_type.rb

+# frozen_string_literal: true
+
+class IndexMembersOnUserIdSourceIdSourceType < ActiveRecord::Migration[6.0]
+  include Gitlab::Database::MigrationHelpers
+
+  disable_ddl_transaction!
+
+  INDEX_NAME = 'index_members_on_user_id_source_id_source_type'
+
+  def up
+    add_concurrent_index(:members, [:user_id, :source_id, :source_type], name: INDEX_NAME)
+  end
+
+  def down
+    remove_concurrent_index_by_name(:members, INDEX_NAME)
+  end
+end

db/post_migrate/20210409185531_remove_members_index_on_user_id.rb

+# frozen_string_literal: true
+
+class RemoveMembersIndexOnUserId < ActiveRecord::Migration[6.0]
+  include Gitlab::Database::MigrationHelpers
+
+  disable_ddl_transaction!
+
+  INDEX_NAME = 'index_members_on_user_id'
+
+  def up
+    remove_concurrent_index_by_name(:members, INDEX_NAME)
+  end
+
+  def down
+    add_concurrent_index(:members, :user_id, name: INDEX_NAME)
+  end
+end

db/schema_migrations/20210409185501

+3655b51b9975a73f3b141f53a0e89aba5b90a030abb8f1dfec3d3bcbb08aa1ec
\ No newline at end of file

db/schema_migrations/20210409185531

+1ecd19849ca362a360719c46893f793ffc52b08bd85603305e3fd4d43f3b7ef2
\ No newline at end of file

db/structure.sql

@@ -23018,10 +23018,10 @@ CREATE INDEX index_members_on_requested_at ON members USING btree (requested_at)
 CREATE INDEX index_members_on_source_id_and_source_type ON members USING btree (source_id, source_type);
-CREATE INDEX index_members_on_user_id ON members USING btree (user_id);
-
 CREATE INDEX index_members_on_user_id_created_at ON members USING btree (user_id, created_at) WHERE ((ldap = true) AND ((type)::text = 'GroupMember'::text) AND ((source_type)::text = 'Namespace'::text));
+CREATE INDEX index_members_on_user_id_source_id_source_type ON members USING btree (user_id, source_id, source_type);
+
 CREATE INDEX index_merge_request_assignees_on_merge_request_id ON merge_request_assignees USING btree (merge_request_id);
 CREATE UNIQUE INDEX index_merge_request_assignees_on_merge_request_id_and_user_id ON merge_request_assignees USING btree (merge_request_id, user_id);