Re: [CI] Query

[David B. Z. <dav...@co...>]

Ramachandra Pai wrote:

> Hi,
>     Trying to educate myself on CI.
>
>     Looking at the features published on the web page,
> I did not find any support for global reliable ordered
> messaging between nodes of the cluster.

Our ICS communication layer guarantees reliable messages between nodes.
Ordering is NOT performed by the communication layer.  We have multiple service
daemons available to process incoming messages, even if the messages were
ordered, we'd have to limit the service daemons in order to guarantee that they
are processed in the order they arrived.

>
>
>     How does any subsystem relying on CI make sure
> that messages sent by any node in the cluster to
> everybody else is seen in the same order on all the
> nodes. Isn't this kind of feature neccessary for SSI
> or any other clients of CI? If so how is that
> accomplished?

We built full SSI on UNIXWARE without complete ordering between nodes.  I worked
on a filesystem token (lock) manager which ordered just the token messages
between nodes.  This mechanism was component specific and did not interact with
any other sub-system.  The token sub-system ordering took 450 lines of code to
perform.  Other sub-systems do not perform any ordering.  As a matter of fact
when we wrote the code, we always assumed that a receiving node may "process"
incoming messages in order.  Think of an SMP machine which has multiple service
daemons handling incoming messages. That means multiple message are even handled
simultaneously!

--
David B. Zafman                             | Compaq Computer Corporation
mailto:dav...@co... | http://www.compaq.com
"Thus spake the master programmer:  When you have learned to snatch
the error code from the trap frame, it will be time for you to leave."