title: DateTieredCompaction without Timestamp Col
body: <p>I think this question: <a href="https://stackoverflow.com/questions/28827489/does-datetieredcompactionstrategy-work-with-composite-keys">Does DateTieredCompactionStrategy work with composite keys?</a> is essentially the same question, but I would like to confirm..</p>
  
  <p>My table (simplified) looks like:
  CREATE TABLE foo (
  name text, 
  textId text, 
  message text
  PRIMARY KEY 
  ((name),textId)) 
  WITH CLUSTERING ORDER BY (textId ASC)</p>
  
  <p>We see here we have no TIMESTAMP column, which to confirm is in fact not needed for DataTieredCompaction, (since this strategy leverages the actual write time, correct?)</p>
  
  <p>The textId does in fact have 'TS' encoded in, which is close the actual writeTimeStamp, but will vary a little bit.</p>
  
  <p>Are use case is, all data is inserted (never updated), with a TTL.
  In most cases we expect the records to be deleted prior to TTL.  Does this sound like an appropriate use for DateTieredCompaction? If not why not?</p>
  
  <p>I've started running some tests, and it does appear to working so far, but will require longer runs (In particular I'm trying to avoid an issue we saw before..where we saw performance plummet after x amount time, which I believe is either due heavy compaction and/or repair processes (we were running on 3 node cluster with LevelTieredCompaction), but have moved up to a 5 node cluster, in the hopes repair will only slow down 2 of the nodes at a time, leaving a full quorum operational at ~100% performance.  (In fact for our use case, we may have a dedicated cluster with repair turned off, and replication factor 1 (we self replicate to other DCs)</p>
  
  <p>Thoughts?</p>
  
  <p>ps. We are running cassandra 2.1</p>