title: Amazon redshift large table VACUUM REINDEX issue
body: <p>My table is 500gb large with 8+ billion rows, INTERLEAVED SORTED by 4 keys. 
  One of the keys has a big skew 680+. On running a VACUUM REINDEX, its taking very long, about 5 hours for every billion rows.</p>
  
  <p>When i track the vacuum progress it says the following:</p>
  
  <pre><code>SELECT * FROM svv_vacuum_progress;
           table_name          |                                        status                                        | time_remaining_estimate 
  -----------------------------+--------------------------------------------------------------------------------------+-------------------------
   my_table_name               | Vacuum my_table_name sort (partition: 1761 remaining rows: 7330776383)               | 0m 0s
  </code></pre>
  
  <p>I am wondering how long it will be before it finishes as it is not giving any time estimates as well. Its currently processing partition 1761... is it possible to know how many partitions there are in a certain table? Note these seem to be some storage level lower layer partitions within Redshift.</p>