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by rystsov 3834 days ago
On the site it is written that GoshawkDB doesn't support membership change. Since you system is based on single decree paxos then you can take Raft's joint consensus and apply to plain paxos. Probably it's the simplest and easiest to change membership in paxos cluster.
1 comments
msackman 3834 days ago
I don't think that's the problem though. The problem that I'm thinking of is that when a cluster grows in size, due to the use of consistent hashing, there'll be a set of objects that need to move between nodes. Calculating and achieving that movement is what concerns me. The exact properties are explained early on in http://arxiv.org/abs/1503.04988

I'm not expecting to ever need to model a global property of "these are the set of nodes that are up and running". I always worry about the effect of weird and wacky network issues on such systems.

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rystsov 3834 days ago
By the way, I always was wondering why the schemas with consistent hashing maintained via the ring are more popular approach than treating key space as a line (-∞,+∞), maintaining the explicit map from segments and rays of keys to the replica groups and split the group/segment when replica group becomes too hot or heavy.

IMHO the perfect hashing solves the problem of distributing the data but the load may follow completely different patterns. See theInstagram's Justin Bieber problem.

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msackman 3833 days ago
Yes, you're right. Now where that paper finishes is pretty much where GoshawkDB starts. Because with GoshawkDB, the server controls the object UUId, you can push as much entropy in there as necessary so the problem identified in the paper is gone. However, ultimately what GoshawkDB ends up generating is basically a set of numbers that you interpret as a way to construct an order of the different nodes (it's the path down the tree, as described in the paper). This set of numbers you could intentionally change in order to change the load balancing to exploit locality.

So yes, currently it'll rigorously enforce a uniform balancing. However, it should be possible to move objects around if/when necessary. I doubt that'll be in for 0.2 though!

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