Re: [ws-tx] Ws-at state tables analysis

[Ian Robinson <ian_robinson@uk.ibm.com>]

Peter, I have comments on your last two observations:
>> 6. In the PV table, event "Commit Decision" occurs twice, with obviously
different meanings. The form valid in state Preparing ought really be
called something else (Prepare Decision), and the action name changed to -
it isn't Record Commit, but Record Prepared. [ i think I remember some
earlier discussion on this; apologies if I've forgotten a deliberate
decision; no apologies for raising the point]

"Record Commit" simply means record the decision of the participant to vote
to commit. "Record Prepared" would have exactly the same meaning.
Splitting the "Commit Decision" row into 2 separate rows in the table for
the distinct actions in Preparing and Committing state seems unnecessary.

>> 7. CV table, allows Commit Decision in Preparing. This makes it possible
for the CV to proceed to a commitment, before the participant has replied,
leading to an inconsistent result.  It clearly should not be possible for
CV to get to PreparedSuccess *with respect to this participant* until it
has received Prepared *from this participant*. I'm afraid we need to
re-instate the CV "Prepared" state.

I disagree with this. The "Commit Decision" requires the "Record Vote"
action to have occurred, which requires a wsat:Prepared message in the
Preparing state.


Regards,
Ian


                                                                           
             "Peter Furniss"                                               
             <peter.furniss@er                                             
             ebor.co.uk>                                                To 
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             28/08/2006 22:43                                           cc 
                                                                           
                                                                   Subject 
                                       [ws-tx] Ws-at state tables analysis 
                                                                           
                                                                           
                                                                           
                                                                           
                                                                           
                                                                           




I've applied a state table checker to the WS-AT 2pc tables as in the
current working
draft (in fact, modified an existing checker used for another protocol).

I took the tables as in the Word document,
transferred them to Excel then ran a macro that wrote them out as
tab-separated.
A perl program then reads the tables in and runs scenarios on them. This
was using
just the paired CV, PV tables. At each step, each side offers the currently
valid internal
events, and if a message is waiting to be delivered, the delivery event. It
also offers
to drop a message in transit.  The program can accept random choice of the
available actions
or be directed. (script choice and the comprehensive investigation of all
possible actions are
intended).

Checks on correctness are that the tables don't get deadlocked (i.e they
eventually reach None:None) and that the final states are consistent.


The following observations are of increasing significance. 1 and 2 are
utterly trivial are only arise because of the deliberately mechinical
loading of the tester; 3 - 6 are are peculiarities and inconsistencies that
reduce the quality of the tables. 7 is a bug.

1. CV, Preparing/Commit Decision: the new state is stated as "Prepared
Success", but the state name has no space in it.
2. PV, Active/Rollback Decision : the new state is "Aborting " with a
spurious trailing space

3. Now we have regularised CV state Aborting [to mean "I am waiting for an
Aborted reply to the
sent Rollback" (regularised as a result of 081 - previously it covered both
this and a received Aborted], it is appropriate to define Comms Times Out
in Aborting state, with action Resend Rollback/Aborting. Without it, if a
message is lost the state machines get stuck, with the coordinator in
Aborting, participant in None.

4. For determining final states, I considered that the coordinator
committed iff it the internal event "Write Done" occurred, and that the
participant committed iff it performed "Initiate Commit Decision"; rolled
back if it performed "Initiate Rollback" and went read-only if it sent
ReadOnly.

However, there is an inconsistency with PV Rollback Decision, which just
has the action "Send Aborted", whereas all the other rollback initiations,
have "Initiate Rollback, Send Aborted, and Forget".  For consistency,
shouldn't the PV Rollback Decision cells have the same actions as e.g.
Expires Times Out, receiving Rollback, Write Failed ?  (c.f issue 038; the
new issue 090 may affect the Forget action and the resulting state, but
Initiate Rollback would seem to be needed anyway)

5. PV table has All Forgotten/None with transition None.  This doesn't seem
consistent with the usual interpretation of state None, that the bilateral
relationship is extinct, and internal events do not occur for it. This may
be sorted out by changes from issue 090.

6. In the PV table, event "Commit Decision" occurs twice, with obviously
different meanings. The form valid in state Preparing ought really be
called something else (Prepare Decision), and the action name changed to -
it isn't Record Commit, but Record Prepared. [ i think I remember some
earlier discussion on this; apologies if I've forgotten a deliberate
decision; no apologies for raising the point]

7. CV table, allows Commit Decision in Preparing. This makes it possible
for the CV to proceed to a commitment, before the participant has replied,
leading to an inconsistent result.  It clearly should not be possible for
CV to get to PreparedSuccess *with respect to this participant* until it
has received Prepared *from this participant*. I'm afraid we need to
re-instate the CV "Prepared" state.


I've not mentioned inconsistencies that are addressed in issue 090.


Peter