Add index to improve performance

of the projects deployments API endpoint.

changelogs/unreleased/mk-add-index-for-project-deployments-with-environment-id-and-updated-at.yml

+---
+title: Add index to improve project deployments endpoint performance
+merge_request: 57554
+author:
+type: performance

db/migrate/20210326035553_add_index_for_project_deployments_with_environment_id_and_updated_at.rb

+# frozen_string_literal: true
+
+class AddIndexForProjectDeploymentsWithEnvironmentIdAndUpdatedAt < ActiveRecord::Migration[6.0]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  INDEX_NAME = 'index_deployments_on_project_and_environment_and_updated_at'
+
+  def up
+    add_concurrent_index :deployments, [:project_id, :environment_id, :updated_at], name: INDEX_NAME
+  end
+
+  def down
+    remove_concurrent_index_by_name :deployments, INDEX_NAME
+  end
+end

db/schema_migrations/20210326035553

+018381c15d859a777afb2b3402ca4425ce52ab35dcd4d1e930b3a9928b2a2019
\ No newline at end of file

db/structure.sql

@@ -22462,6 +22462,8 @@ CREATE INDEX index_deployments_on_id_and_status_and_created_at ON deployments US
 
 CREATE INDEX index_deployments_on_id_where_cluster_id_present ON deployments USING btree (id) WHERE (cluster_id IS NOT NULL);
 
+CREATE INDEX index_deployments_on_project_and_environment_and_updated_at ON deployments USING btree (project_id, environment_id, updated_at);
+
 CREATE INDEX index_deployments_on_project_and_finished ON deployments USING btree (project_id, finished_at) WHERE (status = 2);
 
 CREATE INDEX index_deployments_on_project_id_and_id ON deployments USING btree (project_id, id DESC);