[infinispan-dev] default value for virtualNodes

[Galder Zamarreño]

To reiterate what I said in another thread, the memory effects of virtual nodes on on Hot Rod clients is none since version 1.1 of the protocol (included in 5.1). 

I enhanced the protocol so that clients would generate virtual node hashes and so avoid sending them over the wire.

Cheers,

On Jan 27, 2012, at 4:19 PM, Manik Surtani wrote:

> Good stuff!  Thanks for this.  Yes, I'm ok with numVirtualNodes=48 as a default.  Galder, your thoughts from a Hot Rod perspective?
> 
> On 27 Jan 2012, at 08:41, Dan Berindei wrote:
> 
>> Hi guys
>> 
>> I've been working on a test to search for an optimal default value here:
>> https://github.com/danberindei/infinispan/commit/983c0328dc40be9609fcabb767dd46f9b98af464
>> 
>> I'm measuring both the number of keys for which a node is primary
>> owner and the number of keys for which it is one of the owners
>> compared to the ideal distribution (K/N keys on each node). The former
>> tells us how much more work the node could be expected to do, the
>> latter how much memory the node is likely to need.
>> 
>> I'm only running 10000 loops, so the max figure is not the absolute
>> maximum. But it's certainly bigger than the 0.9999 percentile.
>> 
>> The full results are here:
>> http://fpaste.org/cI1r/
>> 
>> The uniformity of the distribution goes up with the number of virtual
>> nodes but down with the number of physical nodes. I think we should go
>> with a default of 48 nodes (or 50 if you prefer decimal). With 32
>> nodes, there's only a 0.1% chance that a node will hold more than 1.35
>> * K/N keys, and a 0.1% chance that the node will be primary owner for
>> more than 1.5 * K/N keys.
>> 
>> We could go higher, but we run against the risk of node addresses
>> colliding on the hash wheel. According to the formula on the Birthday
>> Paradox page (http://en.wikipedia.org/wiki/Birthday_problem), we only
>> need 2072 addresses on our 2^31 hash wheel to get a 0.1% chance of
>> collision. That means 21 nodes * 96 virtual nodes, 32 nodes * 64
>> virtual nodes or 43 nodes * 48 virtual nodes.
>> 
>> Cheers
>> Dan
>> 
>> 
>> On Fri, Jan 27, 2012 at 12:37 AM, Sanne Grinovero <sanne at infinispan.org> wrote:
>>> On 26 January 2012 22:29, Manik Surtani <manik at jboss.org> wrote:
>>>> 
>>>> On 26 Jan 2012, at 20:16, Sanne Grinovero wrote:
>>>> 
>>>> +1
>>>> Which default? 100? A prime?
>>>> 
>>>> We should also make sure the CH function is optimized for this being on.
>>>> 
>>>> 
>>>> Yes, we should profile a session with vnodes enabled.
>>> 
>>> Manik, we're using VNodes in our performance tests. The proposal is if
>>> we can provide a good default value, as the feature is currently
>>> disabled by default.
>>> 
>>> Cheers,
>>> Sanne
>>> 
>>>> 
>>>> 
>>>> --
>>>> Manik Surtani
>>>> manik at jboss.org
>>>> twitter.com/maniksurtani
>>>> 
>>>> Lead, Infinispan
>>>> http://www.infinispan.org
>>>> 
>>>> 
>>>> 
>>>> 
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> 
> --
> Manik Surtani
> manik at jboss.org
> twitter.com/maniksurtani
> 
> Lead, Infinispan
> http://www.infinispan.org
> 
> 
> 
> 
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--
Galder Zamarreño
Sr. Software Engineer
Infinispan, JBoss Cache