title: Performance impact on primary instance when querying read-only replica
body: <p>I am currently working on an application that continuously queries a database for real time data to be displayed. </p>
  
  <p>In order to have minimal impact on systems which are writing to database, which are essential to the business operation, I am connecting to the Read Only replica in the availability group directly (using the read only replica server name as opposed to Read Only routing via the Always On listener by means of <code>applicationintent=readonly</code>).
  Even in doing so we are noticing response time increases on the inserting of data to the primary server.</p>
  
  <p>To my understanding of secondary replicas this should not be the case. I am using <code>NOLOCK</code> hints in the query as well. I am very perplexed by this and do not quite understand what is causing this increase in response times. All I have thought of so far is that SQL is, regardless of the <code>NOLOCK</code> hint, locking the table I am reading from and preventing the synchronous replication to the read only replica, which is in turn locking the primary instances table, which is holding up the insert query.</p>
  
  <p>Is this the case or is there something I am not quite understanding with regard to Always on Read only replicas?</p>