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From Lahiru Sandaruwan <lahi...@wso2.com>
Subject Re: [Autoscaling] [Improvement] Introducing "curve fitting" for stat prediction algorithm of Autoscaler
Date Tue, 11 Nov 2014 18:00:35 GMT
```Also this is a good read to learn how Netflix use these algorithms for
scaling.

http://techblog.netflix.com/search/label/prediction

On Tue, Nov 11, 2014 at 11:07 PM, Lahiru Sandaruwan <lahirus@wso2.com>
wrote:

> Hi Seshika,
>
> Thanks for the detailed response,
>
> On Tue, Nov 11, 2014 at 10:08 PM, Seshika Fernando <seshika@wso2.com>
> wrote:
>
>> Hi all,
>>
>>
>> a. The timeseries extension to CEP which supports uni-variate and
>> multi-variate linear regression [1] can be used for this. We can use the
>> multi-variate regression to solve the curve fitting stated in Lahiru's
>> email. Basically what we need to do is use *t *and *t^2* as x1 and x2.
>> There by if we run linear regression we get  a,b,c such that V=a+b*t+c*t^2.
>>
>
> Nice to see this exists in CEP already :)
>
> +1 for using multi-variate regression to the curve fitting. Is it
> available in CEP 3.1.0? or can we plug it to 3.1.0?
>
>
>
>> As Lasantha has mentioned we do have a forecasting facility as well, but
>> currently it only works for uni-variate regression, which is not the case
>> here. But if you really need it I might be able to extend it for this
>> use-case, for the moment. You can still use the existing regression
>> facility to determine the coefficients and do the forecasting yourself
>> (which is just plugging those values in to the above equation, with the
>> relevant t values.
>> Let me also just mention, that even though the function is 'linear'
>> regression, we can use linear regression to fit polynomial curves as long
>> as we know the degree of the polynomial function (which in this case we do).
>>
>>
> In Stratos case, i would like to have the forecasting flexibility in
> Autoscaler side. Because then we can let the user decide prediction time
> duration even in runtime.
>
> BTW. Is it possible to do this in CEP, by redeploying execution plans or
> so?
>
> b. Can't we also consider using exponentially weighted moving averages for
>> the previous approach. So instead of using average gradient and average
>> second derivative we can use 'decaying windows' in CEP and get the
>> exponentially weighted moving average of the gradient and second
>> derivative. This will eliminate the spawning of new instances due to sudden
>> 'spikes' as we can control the decaying factor such that we give a
>> practically acceptable weightage to the most recent events compared to
>> older events.
>>
>>
> A great thought. Exponentially weighted moving average filter would be a
> good addition for spike avoidance.
>
> Thanks.
>
>
>> Seshika
>>
>> 1. https://docs.wso2.com/display/CEP400/Regression
>>
>> On Tue, Nov 11, 2014 at 8:51 PM, Lasantha Fernando <
>> lasantha.fdo@gmail.com> wrote:
>>
>>> Hi Lahiru,
>>>
>>> Would it be possible to use linear regression already available as
>>> Siddhi extensions in [1] or maybe improve on that existing extensions
>>> to extend it to fit polynomial curves? The code is available here [2].
>>>
>>> I think forecasting is also available which can be useful in this
>>> usecase. WDYT? Just sharing my 2 cents.. :-)
>>>
>>> [1] http://mail.wso2.org/mailarchive/architecture/2014-March/015696.html
>>> [2]
>>> https://github.com/wso2-dev/siddhi/tree/master/modules/siddhi-extensions
>>>
>>> Thanks,
>>> Lasantha
>>>
>>> On Tue, Nov 11, 2014 at 3:58 PM, Lahiru Sandaruwan <lahirus@wso2.com>
>>> wrote:
>>> > Hi all,
>>> >
>>> > This contains the content i already sent to Stratos dev. Idea is to
>>> > highlight and separate the new improvement.
>>> >
>>> > Current implementation
>>> >
>>> > Currently CEP calculates average, gradient, and second derivative and
>>> send
>>> > those values to Autoscaler. Then Autoscaler predicts the values using
>>> S =
>>> > u*t + 0.5*a*t*t.
>>> >
>>> > In this method CEP calculation is not very much accurate as it does not
>>> > consider all the events when calculating the gradient and second
>>> derivative.
>>> > Therefore the equation we apply doesn't yield the best prediction.
>>> >
>>> > Proposed Implementation
>>> >
>>> >
>>> > I think best approach is to do "curve fitting"[1] for received event
>>> sample
>>> > in a particular time window. Refer "Locally weighted linear regression"
>>> > section at [2] for more details.
>>> >
>>> > We would need a second degree polynomial fitter for this, where we can
>>> use
>>> > Apache commons math library for this. Refer the sample at [3], we can
>>> run
>>> > this with any degree. e.g. 2, 3. Just increase the degree to increase
>>> the
>>> > accuracy.
>>> >
>>> > E.g.
>>> > So if get degree 2 polynomial fitter, we will have an equation like
>>> below
>>> > where value(v) is our statistic value and time(t) is the time of event.
>>> >
>>> > Equation we get from received events,
>>> > v = a*t*t + b*t + c
>>> >
>>> > So the solution is,
>>> >
>>> > Find memberwise curves that fits events received in specific
>>> window(say 10
>>> > minutes) at CEP
>>> > Send the parameters of fitted line(a, b, and c in above equation) with
>>> the
>>> > timestamp of last event(T) in the window, to Autoscaler
>>> >
>>> >
>>> > Autoscaler use v = a*t*t + b*t + c function to predict the value in any
>>> > timestamp from the last timestamp
>>> >
>>> > E.g. Say we need to find the value(v) after 1 minute(assuming we
>>> carried all
>>> > the calculations in milliseconds),
>>> >
>>> > v = a * (T+60000) * (T+60000) + b * (T+60000) + c
>>> >
>>> > So we have memberwise predictions and we can find clusterwise
>>> prediction by
>>> > averaging all the memberwise values.
>>> >
>>> >
>>> >
>>> > Thanks.
>>> >
>>> > [1] http://en.wikipedia.org/wiki/Curve_fitting
>>> > [2] http://cs229.stanford.edu/notes/cs229-notes1.pdf
>>> > [3]
>>> http://commons.apache.org/proper/commons-math/userguide/fitting.html
>>> >
>>> >
>>> > --
>>> > --
>>> > Lahiru Sandaruwan
>>> > Committer and PMC member, Apache Stratos,
>>> > Senior Software Engineer,
>>> > WSO2 Inc., http://wso2.com
>>> > lean.enterprise.middleware
>>> >
>>> > email: lahirus@wso2.com blog: http://lahiruwrites.blogspot.com/
>>> >
>>>
>>
>>
>
>
> --
> --
> Lahiru Sandaruwan
> Committer and PMC member, Apache Stratos,
> Senior Software Engineer,
> WSO2 Inc., http://wso2.com
> lean.enterprise.middleware
>
> email: lahirus@wso2.com blog: http://lahiruwrites.blogspot.com/
>
>

--
--
Lahiru Sandaruwan
Committer and PMC member, Apache Stratos,
Senior Software Engineer,
WSO2 Inc., http://wso2.com
lean.enterprise.middleware

email: lahirus@wso2.com blog: http://lahiruwrites.blogspot.com/