Sage Weil wrote:
You mean if, say, some verifiable metadata or a trusted third party stores
that checksum? Sure. This is just pushing the what-has-committed
Yes.
information to some other party, though, who will presumably face the same
problem of requiring a majority for verifiable correctness. This is more
or less what most people do in practice... using Paxos for critical state
and piggybacking the rest of the system's consistency off of that.
More like receiving a guarantee of consensus (just like any signature on
data), while only needing to be able to communicate with a single node.
(This is why Paxos is typically used only for critical cluster
configuration/state, not regular data.)
Yep, I'm working on a config daemon a la Chubby or zookeeper, based on Paxos,
that does just this. :)
Cool. Do you have a URL? I'd be interested in seeing how you diverge
from classic paxos. For Ceph's monitor daemon, the main requirements
(besides strict correctness guarantees) were scalable (distributed) read
access, and a history of state changes. Nothing too unusual.
Is there a URL? Yes. http://linux.yyz.us/projects/cld.html
It it useful? No. It's just a skeleton code right now. I am
experimenting with various Paxos algorithms as we speak, which is why
it's fresh in my mind at the moment.
I also forgot to mention hyperspace, which is another up-and-coming
player in this area, alongside Chubby and zookeeper.
Jeff
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