Re: [DotGNU]transaction logging and roll-back

[Norbert Bollow]

> Well what I was thinking was more of a routing system, should
> one part go down for what ever reason, we could make a server
> check against a know server table and ask to contact the other
> machine on it's behalf.

Yes, we can do this until we have the full system available.

But it's not a complete solution:

Suppose there are two servers, A and B.  Let's say that for some
reason they are no longer able to communicate with each other.
The servers have no way of knowing whether this is because the
other server is down (or completely unreachable), or whether the
other server is happily serving requests while merely the
communication between the two servers has broken down.  (It
could be a misconfigured router, a saturated link, or whatever.)

One way to deal with this situation is the designate server A
the "master" server, and server "B" the "slave" server, and have
server A process all changes to the database while server B
merely mirrors the database and provides read-only access to the
database.  The downside is that if server A is down or network
conditions are bad somewhere between you and server A, then you
cannot make any change to the database.

In many applications (e.g. the authentication database we're
talking about) there will not be many simultanous requests
requests that would change the database in conflicting ways.
Then it will be much better for both servers to "optimistically"
make all requested changes, even though that makes it possible
for conflicting changes to happen to the copies of the databases
on different servers.  Hence the need for a reliable way of
resolving those conflicts, and rolling back those transactions
which should not have happened.

Greetings, Norbert.

-- 
Norbert Bollow, Weidlistr.18, CH-8624 Gruet  (near Zurich, Switzerland)
Your own domain with all your Mailman lists: $15/month http://cisto.com
Business Coaching for Internet Entrepreneurs ---> http://thinkcoach.com
Tel +41 1 972 20 59      Fax +41 1 972 20 69      address@hidden