SQL Server Always On + changing Isolation level of SPID
<p>Is there any reason why I cannot change the isolation level of a spid running against a primary database in an always on configuration?</p>

<p>Scenario: we are running CRM Dynamics upgrade tool. It was being blocked when trying to run the following command in SQL Server:</p>

<pre><code>SET TRANSACTION ISOLATION LEVEL READ COMMITTED
</code></pre>

<p>On checking the error logs for the upgrade tool it says </p>

<blockquote>
  <p>The operation cannot be performed on database "My_CRM_DB" because it is involved in a database mirroring session or an availability group. Some operations are not allowed on a database that is participating in a database mirroring session or in an availability group.</p>
</blockquote>

<p>I'd like to understand why this is. I can't find anything online in technet that says I shouldn't be allowed to set a spid's isolation level to read committed when using AlwaysOn</p>