Re: RFC: Cassandra Virtual Nodes

2012-03-21 Thread Zhu Han
On Tue, Mar 20, 2012 at 11:24 PM, Jeremiah Jordan < jeremiah.jor...@morningstar.com> wrote: > So taking a step back, if we want "vnodes" why can't we just give every > node 100 tokens instead of only one? Seems to me this would have less > impact on the rest of the code. It would just look like

Re: RFC: Cassandra Virtual Nodes

2012-03-21 Thread Jonathan Ellis
A friend pointed out to me privately that I came across pretty harsh in this thread. While I stand by my technical concerns, I do want to acknowledge that Sam's proposal here indicates a strong grasp of the principles involved, and a deeper level of thought into the issues than I think anyone else

Re: RFC: Cassandra Virtual Nodes

2012-03-21 Thread Vijay
>>> I envision vnodes as Cassandra master being a shared cache,memtables, and manager for what we today consider a Cassandra instance. It might be kind of problematic when you are moving the nodes you want the data associated with the node to move too, otherwise it will be a pain to cleanup after

Re: RFC: Cassandra Virtual Nodes

2012-03-21 Thread Edward Capriolo
I just see vnodes as a way to make the problem smaller and by making the problem smaller the overall system is more agile. Aka rather then 1 node streaming 100 gb the 4 nodes stream 25gb. Moves by hand are not so bad because the take 1/4th the time. The most simple vnode implementation is vmware.

Re: RFC: Cassandra Virtual Nodes

2012-03-21 Thread Peter Schuller
> Software wise it is the same deal. Each node streams off only disk 4 > to the new node. I think an implication on software is that if you want to make specific selections of partitions to move, you are effectively incompatible with deterministically generating the mapping of partition to respons

Re: RFC: Cassandra Virtual Nodes

2012-03-21 Thread Edward Capriolo
On Wed, Mar 21, 2012 at 3:24 PM, Tom Wilkie wrote: > Hi Edward > >> 1) No more raid 0. If a machine is responsible for 4 vnodes they >> should correspond to for JBOD. > > So each vnode corresponds to a disk?  I suppose we could have a > separate data directory per disk, but I think this should be

Re: RFC: Cassandra Virtual Nodes

2012-03-21 Thread Jonathan Ellis
On Wed, Mar 21, 2012 at 8:50 AM, Eric Evans wrote: > I must admit I find this a little disheartening.  The discussion has > barely started.  No one has had a chance to discuss implementation > specifics so that the rest of us could understand *how* disruptive it > would be (a necessary requirement

Re: RFC: Cassandra Virtual Nodes

2012-03-21 Thread Tom Wilkie
Hi Edward > 1) No more raid 0. If a machine is responsible for 4 vnodes they > should correspond to for JBOD. So each vnode corresponds to a disk? I suppose we could have a separate data directory per disk, but I think this should be a separate, subsequent change. However, do note that making t

Re: RFC: Cassandra Virtual Nodes

2012-03-21 Thread Chris Goffinet
I'm going to agree with Eric on this one. Twitter has wanted some sort of vnode support for quite sometime. We even were willing to do all the work. I have reservations about that now We have been silent due to the community and how this is more like an exclusive Datastax project than an Apache

Re: RFC: Cassandra Virtual Nodes

2012-03-21 Thread Edward Capriolo
On Wed, Mar 21, 2012 at 9:50 AM, Eric Evans wrote: > On Tue, Mar 20, 2012 at 9:53 PM, Jonathan Ellis wrote: >> It's reasonable that we can attach different levels of importance to >> these things.  Taking a step back, I have two main points: >> >> 1) vnodes add enormous complexity to *many* parts

Re: RFC: Cassandra Virtual Nodes

2012-03-21 Thread Eric Evans
On Tue, Mar 20, 2012 at 9:53 PM, Jonathan Ellis wrote: > It's reasonable that we can attach different levels of importance to > these things.  Taking a step back, I have two main points: > > 1) vnodes add enormous complexity to *many* parts of Cassandra.  I'm > skeptical of the cost:benefit ratio