title: Why do deadlocks happen in SQL Server?
body: <p>So as I understand it, SQL deadlocks happen when a SPID is busy processing another query and it can't be bothered to run another one because it's so busy right now. The SQL Server "randomly" picks one of the queries to deadlock out of the resources asked for and fails it out, throwing an exception.</p>
  
  <p>I have an app running ~ 40 instances and a back-end Windows Service, all of which are hitting the same database. I'm looking to reduce deadlocks so I can increase the number of threads I can runs simultaneously.</p>
  
  <ol>
  <li>Why can't SQL Server just enqueue the new query and run it when it has time and the resources are available? Most of what I'm doing can wait a few seconds on occasion.</li>
  <li>Is there a way to set <strong>Transaction Isolation Level</strong> globally without having to specify it at the onset of each new connection/session?</li>
  </ol>