y stale results.  Asynchronous communication
  is used when synchronous would be too slow.
 </P
><P
>  Solutions can also be categorized by their granularity.  Some solutions
  can deal only with an entire database server, while others allow control
  at the per-table or per-database level.
 </P
><P
>  Performance must be considered in any choice.  There is usually a
  trade-off between functionality and
  performance.  For example, a fully synchronous solution over a slow
  network might cut performance by