检查mysql与远程主机的连接

Question

I have model to store database connection parameters (host, database name, username, password) and filling it by form. Before create or update I need to check if connection be good with entered parameters. I create validate :check_connection validator:

# don`t change primary connection
class Remote < ActiveRecord::Base; end

def check_connection
  return if errors.any? || (!new_record? && password.empty?)
  begin
    Remote.establish_connection(
      adapter: 'mysql2',
      host: host,
      username: username,
      password: password,
      database: database,
      connect_timeout: 5,
      reconnect: false
    )
    # maybe need to make some sql request? did try it
  rescue Exception => e
    errors.add :connection, 'Could not connect to database'
  end
end

When I try enter accessible host ( localhost ), code like above works good. But if host like 192.168.1.1 (unaccessible) page freezing after submit form. I see attempts to connect every second and it did not stop after ESC (stop loading page) at browser (I see attempts at tcpdump on network interface). And attempts did not stop..

So, how can I validate connection to database? And if connection can not be established page must will not be load long time.

Answer 1

I did use gem 'mysql2' and bundle install 0.3.11 version. This version ignore connect_timeout and bug fixed at newer version. After I try 0.3.12b4 ( gem 'mysql2', '~> 0.3.12b4' ) all works fine.

Answer 2

Variable connect_timeout is a global variable. Therefore, mysql2 maybe ignore it.

on mysql5.6:

mysql[(none)]> set connect_timeout = 123;
ERROR 1229 (HY000): Variable 'connect_timeout' is a GLOBAL variable and should be set with SET GLOBAL

I set timeout variables when initializing mysql2 but it's not reflected. A README of mysql2 says that you can set the *timeout options, but I think the README is outdated or broken.

on mysql2 0.3.14(gem):

client =  Mysql2::Client.new(
  host: 'localhost',
  database: 'test',
  username: 'root',
  password: '',
  connect_timeout: 3,
  read_timeout: 3,
  write_timeout: 3,
  wait_timeout: 3);

client.query('show variables like "%timeout%"').map{|r| [r["Variable_name"], r["Value"]] }

=> [["connect_timeout", "10"],
 ["delayed_insert_timeout", "300"],
 ["innodb_lock_wait_timeout", "50"],
 ["innodb_rollback_on_timeout", "OFF"],
 ["interactive_timeout", "28800"],
 ["lock_wait_timeout", "31536000"],
 ["net_read_timeout", "30"],  # Maybe older mysql has read_timeout?
 ["net_write_timeout", "60"], # Maybe older mysql has write_timeout?
 ["slave_net_timeout", "3600"],
 ["wait_timeout", "28800"]]

If you use ActiveRecord , you can set only wait_timeout variable by database.yml .

in database.yml:

development:
  adapter: mysql2
  encoding: utf8
  charset: utf8
  database: test
  pool: 5
  username: root
  password: 
  host: localhost
  connect_timeout: 3
  read_timeout: 3
  write_timeout: 3
  wait_timeout: 3

A result of ActiveRecord 4.0.1:

> ActiveRecord::Base.connection.execute('show variables like "%timeout%"').to_a
=> [["connect_timeout", "10"],
 ["delayed_insert_timeout", "300"],
 ["innodb_flush_log_at_timeout", "1"],
 ["innodb_lock_wait_timeout", "50"],
 ["innodb_rollback_on_timeout", "OFF"],
 ["interactive_timeout", "28800"],
 ["lock_wait_timeout", "31536000"],
 ["net_read_timeout", "30"],
 ["net_write_timeout", "60"],
 ["rpl_stop_slave_timeout", "31536000"],
 ["slave_net_timeout", "3600"],
 ["wait_timeout", "3"]]

ActiveRecord set wait_timeout variable in abstract_mysql_adapter.rb .

see:

abstract_mysql_adapter.rb https://github.com/rails/rails/blob/master/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb

mysql2_adapter.rb https://github.com/rails/rails/blob/master/activerecord/lib/active_record/connection_adapters/mysql2_adapter.rb