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Re: [Vrs-development] IBM Token Ring Thingy...
From: |
Eric Altendorf |
Subject: |
Re: [Vrs-development] IBM Token Ring Thingy... |
Date: |
Fri, 3 May 2002 10:31:43 -0700 |
On Friday 03 May 2002 07:20, Chris Smith wrote:
> Yep, but you've still got the problem of two or more LDS's broadcasting the
> 'claim cluster image' to the cluster. You can't have more than one
> claiming the cluster image, so this should fail. However, it's really
> difficult to engineer because you've got to detect that all nodes in the
> cluster accepted the SAME claim message from the same LDS. This is hard
> enough, without the added complication that you may not know about all
> LDS's in the cluster.
>
> This is why the MA approach may help. Each LDS maintains it's own view of
> the cluster image, and is kept in sync as best as possible. It doesn't
> have to be immediate (and I think we should design with this in mind)
> because we have to deal with the case of LDS's going offline and coming
> back. Thus the MA idea allows all scenarios to be dealt with. If an LDS
> comes back on line, then a lot might have changed, and the MA 'data tree'
> will return a wealth of information.
OK, I'm starting to see the picture here with the MA.
I think what it boils down to is that if we have no requirement for the
cluster images to remain consistent among machines, then there are a number
of different mechanisms we could use.
If we want to guarantee that the CI remains consistent, or remains "at most X
minutes out of date" or anything else, I think we're going to have to resort
to transactions. Pretty much ANY time we want to make a guarantee about data
consistency across a distributed network, we're going to have to use
distributed transactions with two phase commit.
By the way -- I would strongly recommend that anyone working on this project
go to a library and read *Transaction Processing: Concepts and Techniques" by
Jim Gray and Andreas Reuter. There are other books, but that's pretty much
the bible, AFAIK.
Eric
--
"First they ignore you. Then they laugh at you.
Then they fight you. And then you win." -Gandhi