RE: [ws-caf] 2PC or 3PC

An interesting piece of work in this area is Lamport/Gray Paxos Commit. Subject to patent, as I understand it.

Alastair

-----Original Message-----
From: Guy Pardon [mailto:guy@atomikos.com]
Sent: 24 May 2004 13:58
To: ws-caf@lists.oasis-open.org
Subject: [ws-caf] 2PC or 3PC

Hi all,

Sorry for my long absence, but now I am finally trying to get involved again into CAF.

Since it is time to start thinking about the CF specs (next step after Context), I was trying to imagine possible practical cases of other protocols for coordination besides 2-phase commit.

Hence the question I would like to discuss: what is the view of this community on the applicability of 3-phase commit (3PC) in SOA architectures?

3PC is generally believed to be better than 2-phase because of its non-blocking character in some situations. It's also mentioned in the initial CF draft text.

But, if I recall correctly, there is a theorem (Nancy Lynch, MIT) which states that distributed agreement is not possible in systems where both nodes and communication can fail and/or time out.

The net practical result is that 3PC can also block (like 2PC) in realistic environments like IIOP, HTTP or any other transport protocol I know.

Due to this, and the increased message overhead (3 rounds instead of 2), it seems unlikely to me that this protocol will get significant acceptance in an SOA world. 2PC is simpler and probably just about as good in practice.

I am not saying that 2PC is the only protocol (and that's also not the kind of thread I wanted to start). Instead, I just want to validate my view on 3PC applicability for web services here. I know about the WS-R work going on, but it seems unlikely that this will offer deterministic time limits for message delivery (correct me if I am wrong?). As a result, WS-R falls under the above theorem and will not improve 3PC performance either.

Any thoughts/comments/ideas?

Thanks,

Guy

Dr. Guy Pardon ( guy@atomikos.com )

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