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Posted to dev@stratos.apache.org by "Imesh Gunaratne (JIRA)" <ji...@apache.org> on 2014/11/11 10:38:34 UTC
[jira] [Issue Comment Deleted] (STRATOS-939) CEP sends very large
values for gradient and second derivative of load average
[ https://issues.apache.org/jira/browse/STRATOS-939?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Imesh Gunaratne updated STRATOS-939:
------------------------------------
Comment: was deleted
(was: Hi Nirmal,
According to the discussion we had in dev list, the solution you have provided here seems to be not valid.
As I understood the root cause of this problem is as follows:
- Currently the gradient calculation is done using statistics sent by different members of a cluster. IMO this is not correct. Mixing statistics values sent by different sources might not be correct.
- Imagine there are three instances (m1, m2, m3) in a cluster where each report statistics values as 10, 50 and 80 continuously for tn time period:
t1{10, 50, 80},t2{10, 50, 80},t3 {10, 50, 80},tn {10, 50, 80}
- Now if we calculate the gradient at a point of time using values sent by m1 and m3 (10 and 80) we will find a high gradient value. However at this situation gradient is zero at each member.
Thanks
Imesh)
> CEP sends very large values for gradient and second derivative of load average
> ------------------------------------------------------------------------------
>
> Key: STRATOS-939
> URL: https://issues.apache.org/jira/browse/STRATOS-939
> Project: Stratos
> Issue Type: Bug
> Components: CEP
> Affects Versions: 4.1.0 M3
> Reporter: Nirmal Fernando
> Assignee: Nirmal Fernando
> Priority: Critical
> Fix For: 4.1.0 M4
>
> Attachments: STRATOS-939.diff
>
>
> How we calculate gradient of two events?
> Say the events are; e1(t1,v1) and e2(t2,v2)
> tx - time in milliseconds when xth event occurred
> vx - value (memory, cpu etc.) that xth event carries
> time gap = t(2-1) = t2 -t1 milliseconds
> time gap in seconds = t(2-1) = (t2 - t1)/1000 seconds
> Hence,
> Gradient = (v2 - v1) / t(2-1) = ( (v2 - v1) * 1000 ) / (t2 - t1)
> I've enabled debug logs for CEP extension;
> log4j.logger.org.apache.stratos.cep.extension=DEBUG
> Please find the following 3 logs extracted from the debug logs;
> ===================================================================
> TID: [0] [STRATOS] [2014-11-05 19:47:27,073] DEBUG {org.apache.stratos.cep.extension.SecondDerivativeFinderWindowProcessor} - Gradient: -0.1996007984031936 Last val: 9.0 First val: 12.0 Time Gap: 15030 t1: 1415213202095 t2: 1415213217125 hash: 155426542
> TID: [0] [STRATOS] [2014-11-05 19:47:27,073] DEBUG {org.apache.stratos.cep.extension.SecondDerivativeFinderWindowProcessor} - Gradient: -999.9999999999998 Last val: 7.000000000000001 First val: 12.0 Time Gap: 5 t1: 1415213232152 t2: 1415213232157 hash: 155426542
> TID: [0] [STRATOS] [2014-11-05 19:47:27,074] DEBUG {org.apache.stratos.cep.extension.SecondDerivativeFinderWindowProcessor} - Gradient: -44.34884666437174 Last val: -999.9999999999998 First val: -0.1996007984031936 Time Gap: 22544 t1: 1415213209610 t2: 1415213232154 hash: 155426542
> ===================================================================
> So, as you can see the reason behind a large value is when the time gap between two subjected events is less than 1 second. This could happen since events are coming from different asynchronous agents and also when there are less number of events.
> FIX
> ====
> So, the fix I propose is a very simple one and it will not compromise anything AFAIS.
> Fix is to calculate time gap as follows;
>
>
> time gap = t(2-1) } t2 -t1 > 1000 -----> t2 - t1
> t2 - t1 <= 1000 ----> 1000
> I have tested this and works fine.
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