title: global temporary table in hibernate
body: <p>In update mode of hbm2ddl.auto hibernate creates global temporary table like below,</p>
  
  <pre><code>Hibernate: create global temporary table HT_PASSENGER_VEHICLE (VEHICLE_ID number(10,0) not null) on commit delete rows
  Hibernate: create global temporary table HT_TRANSPORTATION_VEHICLE (VEHICLE_ID number(10,0) not null) on commit delete rows
  Hibernate: create global temporary table HT_VEHICLE (VEHICLE_ID number(10,0) not null) on commit delete rows
  </code></pre>
  
  <p>what are these tables? are these related to cache mechanism?
  why hibernate creates these tables?</p>