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From aaron morton <aa...@thelastpickle.com>
Subject Re: Host score calculation for dynamic_snitch
Date Sun, 10 Apr 2011 01:23:04 GMT
Recent discussion on dynamic snitch for some background http://www.mail-archive.com/user@cassandra.apache.org/msg12089.html



1) Adapted phi failure detector as used by gossip, see o.a.c.locator.DynamicEndpointSnitch
2) tracks last 100 responses from a node 
3) in memory only
4) it's expensive when compared to storing a latency. It loops through all known nodes and
calcs it's score which requires looping through all scores. 

Aaron

On 9 Apr 2011, at 08:27, A J wrote:

> dynamic_snitch seems to do host score calculation to figure the
> latency of each node.
> 
> What are the details of this calculation :
> 1. What is the mechanism to determine latency ?
> 2. Does it score the calculated scores and use the historical figures
> to come up with the latest scores ? (You can't just base the latency
> based on a singular ping)
> 3. Where are these scores stored ? In the cassandra database somewhere ?
> 4. cassandra.yaml also says that dynamic_snitch_update_interval_in_ms
> "controls how often to perform the more expensive part of host score
> calculation". What is the expensive part and how expensive is it?
> 
> Thanks.


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