3.

Termination in centralized 2PC:
- If a participant times out having voted yes, it must consult the others about
the outcome. Say, P is consulting Q.
- If Q has received the decision from the coordinator, it tells it to P.
- If Q has not yet voted, it can decide to rollback.
- If Q does not know, it can't help.
- If no-one can help, P is blocked.

Termination in decentralized 2PC:
As above expcept the second step.
- If Q has received yes-votes from everyone or no-vote from someone, it tells
P the decision. 

Suppose that we have participants P1,...P6.
Assume that the following has happened
P1 has sent Yes to only P2 and then crashed.
P3 has sent Yes to only P4 and then crashed.
P5 has sent Yes to only P6 and then crashed.

It is not enough if two of the remaining participants exchange
information to see that everyone has voted Yes. However, if everyone's
information is collected together, this is possible. Therefore, it is
possible to enhance termination by consulting all other participants.