Optimize ldap keys counters query performance for usage data

changelogs/unreleased/208234-optimize-ldap-keys-in-usage-data.yml

+---
+title: Optimize ldap keys counters query performance in usage data
+merge_request: 27309
+author:
+type: performance

db/migrate/20200316111759_add_index_on_id_and_ldap_key_to_keys.rb

+# frozen_string_literal: true
+
+class AddIndexOnIdAndLdapKeyToKeys < ActiveRecord::Migration[6.0]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+  INDEX_NAME = 'index_keys_on_id_and_ldap_key_type'
+
+  disable_ddl_transaction!
+
+  def up
+    add_concurrent_index :keys, [:id, :type], where: "type = 'LDAPKey'", name: INDEX_NAME
+  end
+
+  def down
+    remove_concurrent_index :keys, INDEX_NAME
+  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: 2020_03_13_123934) do
+ActiveRecord::Schema.define(version: 2020_03_16_111759) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "pg_trgm"
@@ -2309,6 +2309,7 @@ ActiveRecord::Schema.define(version: 2020_03_13_123934) do
     t.datetime_with_timezone "expires_at"
     t.index ["fingerprint"], name: "index_keys_on_fingerprint", unique: true
     t.index ["fingerprint_sha256"], name: "index_keys_on_fingerprint_sha256"
+    t.index ["id", "type"], name: "index_keys_on_id_and_ldap_key_type", where: "((type)::text = 'LDAPKey'::text)"
     t.index ["id", "type"], name: "index_on_deploy_keys_id_and_type_and_public", unique: true, where: "(public = true)"
     t.index ["last_used_at"], name: "index_keys_on_last_used_at", order: "DESC NULLS LAST"
     t.index ["user_id"], name: "index_keys_on_user_id"