Distributed Transaction Management, Autumn 2003 , Exercise 6
Due Tue 02.12.2003

1. Create another example (not payments like in slides),
where nested txns seem to be reasonable in that there
may be an aborting subtxn but even then the top-level
txn will commit. Draw a txn tree and explain how the
processing might proceed.

2. Let us assume the following events:
Server X initiates a TIP txn.
X pushes the txn is to server Y.
Y pushes the txn is to server Z.
X initiates 2PC and all vote yes.
Write down the sequence of messages exchanged.

3. Let us assume the following events:
Server X initiates a TIP txn.
X pushes the txn to server Y.
Y pushes the txn to server Z.
Y pushes the txn to server U.
U pushes the txn to server W, which can not commit
the txn.
X initiates 2PC and all but U vote yes.
Write down the sequence of messages exchanged.


4. Show that one-phase commit in TIP may violate
atomicity (that is, there may be someone committing
and someone else aborting). For this,  you need more than
two participants in the participant tree.

5. Give a condition under which one-phase commit can be
done safely in TIP.