title: mysql insert into.. on duplicate key update - auto_increment issue
body: <p>I need to perform bulk <code>INSERT IGNORE</code> with <code>ON DUPLICATE KEY UPDATE</code> and I'm facing the following problem.</p>
  
  <p>I perform 20 million updates daily on a table of around 20 million. Only a few dozen thousand new rows are added daily.</p>
  
  <p>If I use <code>innodb_autoinc_lock_mode = 0</code> I'm losing concurrent performance, but the ID increments only when rows are inserted.</p>
  
  <p>If I use <code>innodb_autoinc_lock_mode = 1</code> I gain concurrency, but the ID field increments by 20 million daily, and it would max out an <code>INT</code> in under 4 months.</p>
  
  <p>I could use a <code>BIGINT</code> and I wouldn't run out of ID space even with updates, but this seems a bit hacky. Is this the preferable solution in my case?</p>