title: MySQL - INSERT queries taking long time
body: <p>I have a table with about 10.000 rows. 
  Structure of the table is:</p>
  
  <pre><code>CREATE TABLE IF NOT EXISTS `demands` (
    `cycle_id` int(11) NOT NULL,
    `subject_id` varchar(45) COLLATE utf8_unicode_ci NOT NULL,
    `market_id` int(11) NOT NULL,
    `price` int(11) NOT NULL,
    `currency_id` varchar(45) COLLATE utf8_unicode_ci DEFAULT NULL,
    `amount` bigint(20) DEFAULT NULL
  ) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;
  </code></pre>
  
  <p>Keys:</p>
  
  <ul>
  <li>PRIMARY (cycle_id, subject_id, market_id, price)</li>
  <li>FK1 (market_id)</li>
  <li>FK2 (subject_id)</li>
  <li>FK3 (currency_id)</li>
  </ul>
  
  <p>Query like this offen takes long time (about 1s):</p>
  
  <pre><code>INSERT INTO poptavky VALUES 
    (4, 'user', 17, 110, 'pound', 110) ,
    (4, 'user', 17, 90, 'pound', 120) , 
    (4, 'user', 17, 70, 'pound', 130) ; 
  </code></pre>
  
  <p>Where could be the problem?
  Thanks</p>