title: Why BigQuery BI engine does not use all the reservation?
body: <p>I have a dashboard connected to a BigQuery Table, BI engine works as expected as I am using a calendar filter and my table is partitioned per date.
  when I select a longer date range, BI engine stop working with this message "The table or data volume was larger than BI Engine supports at this time", that's fair.</p>
  
  <p>Please notice, I am already filtering by a partition, but sometimes, I need to see the whole data</p>
  
  <p>to solve that, I created a BI reservation, and I notice regardless of the size 1,2,4 GB the memory used is always 600MB? and I get the same message, I attached a screenshot here, is this by design?</p>
  
  <p><a href="https://i.stack.imgur.com/Y7aq3.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Y7aq3.png" alt="enter image description here"></a></p>
  
  <p>Bug Report here: <a href="https://issuetracker.google.com/issues/150633500" rel="nofollow noreferrer">https://issuetracker.google.com/issues/150633500</a></p>