Shared checkpoints create a group (per checkpoint table) to identify replicas and to pick the active replica.  

All groups use a single checkpoint (SAFplus::Checkpoint Group::mGroupCkpt).  Groups store <????> in this structure because <????>.

But groups can be configured to use an in memory database instead of a checkpoint.  Using this mode has the following features, limitations, and effects:

 1.  ??
 2.  ??


To avoid circular initialization dependencies, Checkpoints initialize themselves with in-memory groups.