anchor.diff:  <2> the type of header is aliased as the name SCQStore.
   <3> the `writePosition` is the first bound value. It is the highest known byte which has been written to and is updated atomically.
   <4> the roll cycle is daily.
  -<5> this class control how it will be indexed on demand.  This adds meta data entries for indexed lookup.
  +<5> this class controls how it will be indexed on demand.  This adds meta data entries for indexed lookup.
   <6> this is the highest message index which was acknowledged by a replica.
   
   For us a key feature of CQ is not just how the data structure is arranged,
  
positive.code: == What is Chronicle Queue?
  
  Chronicle Queue (CQ) is a persisted journal of messages.
  CQ support concurrent writers and readers even across multiple JVMs on the same machine.
  Every reader sees every message and a reader can join at any time and still see every message.
  We assume you can read/scan through messages fast enough that even if you are not interested in most messages it will still be fast enough.
  These are not consumers as such and messages don't disappear after reading them.
  
negative.code:  - a bit to flag whether the message is complete or not.
  
  When the message is not complete, it cannot be read.  However, if the length is known, a writer can skip such messages, attempt to write after it.
  Say Thread1 is in the middle of writing a message, but it knows how long it will be,
  it can write 4 bytes which indicate the length.
  Thread2 can see that there will be a message and skip over it looking for a place to write.
  This way multiple threads can be writing to the queue concurrently.
  Any message which is detected as bad e.g. the thread died, can be marked as meta data and skipped by the reader.
  
  There is a special value which is a "poison pill" value, which indicates the file has been rolled.
  