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From Tamar Fraenkel <ta...@tok-media.com>
Subject Re: increased RF and repair, not working?
Date Mon, 30 Jul 2012 14:46:14 GMT
Thanks!
*Tamar Fraenkel *
Senior Software Engineer, TOK Media

[image: Inline image 1]

tamar@tok-media.com
Tel:   +972 2 6409736
Mob:  +972 54 8356490
Fax:   +972 2 5612956





On Mon, Jul 30, 2012 at 5:30 PM, Tim Wintle <timwintle@gmail.com> wrote:

>
> On Mon, 2012-07-30 at 15:16 +0300, Tamar Fraenkel wrote:
> > How do you make this calculation?
>
> It seems I did make a mistake somewhere before (or I mistyped it) - it
> should have been 2.7%, not 2.8%.
>
>
> You're sending read requests to RF servers, and hoping for a response
> from CL of them within the time.
>
> For N=2, CL=1 - the probability of both hitting the worst 10% latency is
> 0.1 * 0.1 = 1%
>
> For N=3, C=2 - the probability of two of the three servers hitting the
> worst 10% latency is (0.9 * (0.1 * 0.1) ) + (0.1 * ((0.1 * 0.9) + (0.9 *
> 0.1))) = 2.7%
>
>
> Tim
>
>
>
>
> >
> > Thanks,
> > Tamar Fraenkel
> > Senior Software Engineer, TOK Media
> >
> > Inline image 1
> >
> > tamar@tok-media.com
> > Tel:   +972 2 6409736
> > Mob:  +972 54 8356490
> > Fax:   +972 2 5612956
>
> >
>
> >
> > On Mon, Jul 30, 2012 at 3:14 PM, Tim Wintle <timwintle@gmail.com>
> > wrote:
> >         On Mon, 2012-07-30 at 14:40 +0300, Tamar Fraenkel wrote:
> >         > Hi!
> >         > To clarify it a bit more,
> >         > Let's assume the setup is changed to
> >         > RF=3
> >         > W_CL=QUORUM (or two for that matter)
> >         > R_CL=ONE
> >
> >         > The setup will now work for both read and write in case of
> >         one node
> >         > failure.
> >         > What are the disadvantages, other than the disk space needed
> >         to
> >         > replicate everything trice instead of twice? Will it affect
> >         also
> >         > performance?
> >
> >
> >         (I'm also running RF2, W_CL1, R_CL1 atm - so this is
> >         theoretical)
> >
> >         As I understand it, the most significant performance hit will
> >         be to the
> >         variation in response time.
> >
> >         For example with R_CL1, (roughly) 1% of requests will be take
> >         more than
> >         the worst 10% of server response times. With R_CL=QUORUM 2.8%
> >         of
> >         requests will have the same latency. (assuming I've just
> >         calculated that
> >         right)
> >
> >         Tim
> >
> >
> >         >
> >         >
> >
> >
> >
> >
>
>
>

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