3.

Q: Examine the possibilities to use the following rule in termination of 3PC,
 when the network has partitioned?
"Allow a group to recover only, if it contains two different states (and there 
can be at most 2)."


A: Each group elects a new coordinator, except the group that has the original
coordinator. The coordinator polls the states of the members of the group. 
There must be two different states and not more than two. Existence of two 
states ensure that all the participants in the system are in either of those 
two states. 

If the group contains INIT amd ABORT states, 
then all the participants of the group make an ABORT. 

If the group contains INIT and WAIT states, 
then  all the participants of the group make an ABORT. 

If the group contains WAIT and ABORT states, 
then  all the participants of the group make an ABORT.  

If the group contains WAIT and PRECOMMIT states, 
then all the participants of the group make a COMMIT.

If the group contains PRECOMMIT and COMMIT states, 
then all the participants of the group make a COMMIT.