Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!sdd.hp.com!hplabs!hpcc05!hpyhde4!hpycla!hpcuhc!dhepner
From: dhepner@hpcuhc.cup.hp.com (Dan Hepner)
Newsgroups: comp.databases
Subject: Re: two phase commit ???
Message-ID: <2060021@hpcuhc.cup.hp.com>
Date: 29 Jun 91 04:20:49 GMT
References: <1991Jun23.191959.29921@logixwi.uucp>
Organization: Hewlett Packard, Cupertino
Lines: 19

Before getting on an airplane I wrote:

>The only irritant with 2PC is that it is subject to "getting stuck",

Which I went on to explain poorly.

After completing phase 1, a subserviant conceivably can lose contact
with the commit coordinator.  After proper patience, the administrator
of the subserviant machine may decide that the cost of any potential 
inconsistency which may be caused by making some unilateral decision
is overridden by a need to free up resources held by the uncompleted
transaction. This is called by some literature a "heuristic decision".

Most formal specifications of two phase commit anticipate such
an override of the protocol proper, and provide for "someone" to
eventually be notified of what has happened, so long as anyone 
checks. 

Dan Hepner