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From Peter Schuller <peter.schul...@infidyne.com>
Subject Re: CL.ONE reads / RR / badness_threshold interaction
Date Tue, 12 Apr 2011 22:27:55 GMT
> To now answer my own question, the critical points that are different
> from what I said earlier are: that CL.ONE does prefer *one* node (which
> one depending on snitch) and that RR uses digests (which are not
> mentioned on the wiki page [1]) instead of comparing raw requests.

I updated it to mention digest queries with a link to another page to
explain what that is, and why they are used.

> I am assuming that RR digests save on bandwidth, but to generate the
> digest with a row cache miss the same number of disk seeks are required
> (my nemesis is disk io).

Yes. It's only a bandwidth optimization.

> So to increase pinny-ness I'll further reduce RR chance and set a
> badness threshold.  Thanks all.

Just be aware that, assuming I am not missing something, while this
will indeed give you better cache locality under normal circumstances
- once that "closest" node does go down, traffic will then go to a
node which will have potentially zero cache hit rate on that data
since all reads up to that point were taken by the node that just went
down.

So it's not an obvious win depending.

-- 
/ Peter Schuller

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