title: Performance impact of updating an index in SQL Server?
body: <p>I'm working on optimising a database. I'm wondering what the impact is on performance when an update is performed on a non-clustered index column when there are ~9.000.000 records in the table. </p>
  
  <p>I know an update on a clustered index column involves "physical" moving of data. What about a non-clustered one?</p>
  
  <p>I'm looking at an index that is used to seek 68 times but updated 208.000 times at ~9.000.000 records (non-unique). I'm trying to determine the performance tradeoff. Without the index, a full table scan would have been used 68 times instead of the seek (with a runtime of <code>N = ~9.000.000</code>). Is this worse than an update being performed on the index 208.000 times?</p>
  
  <p>Thanks</p>