Re: adaptive threshold significance level
- From: Ls Cheng <exriscer@xxxxxxxxx>
- To: Dragutin Jastrebic <orahawk@xxxxxxxxx>
- Date: Tue, 4 Nov 2014 20:59:47 +0100
Hi Dragutin
I understood the concept after realizaing the threshold was calculated as
sample percentile. Thanks for the explanation though.
What I understand is that adaptive threshold is calculated using samples
from previous days, let's say AAS, if the collected data has 100 samples
from values 0 to 15 and the 99 percentile value is 14 then that will be
used as the critical threshold, if 14 occured twice then a alert will be
raised (the occurance 2 is the default value).
In OEM 12.1.0.4 it no longer recommends the usual adaptive threshold from
the database, OEM now calculates the database threshold itself. I am having
a few issues with advanced threshold management and have a few SR open all
waiting for internal responses :-/
Thanks!
On Tue, Nov 4, 2014 at 8:29 PM, Dragutin Jastrebic <orahawk@xxxxxxxxx>
wrote:
> =>
> By reading the above statement it seems t me that it is saying for warning
> level it will rise an warning alert when 0.05 percent of observations are
> above the threshold and raise a critical alert when it is 0.01 percent.
> Should not it be the opposite? When a higher number of observation is
> higher than the threshold a critical alert should be raised?
> <=
>
> No, it is not the opposite, this is exactly the way it is supposed to
> work, since the Significance Level adaptive treshold is used to capture
> seldom, unusal values,
>
> For exemple, with OEM 12c you have a metric "Average number of active
> sessions", with the
> following defaults:
>
> Very high level (0.99) for a warning treshold
> Extreme level (0.9999) for a critical treshold.
>
> The value that has 1 occurence in 100 will trigger a warning alert, but
> the value that has 1 occurence in 10000 will trigger a critical alert
>
> So more unusual the value is, it is estimated as more critical.
>
> BTW, it seems that OEM 12c with its quick configuration, is mostly
> suggesting Significance Level
> for OLTP and Percentage of Maximum for DW systems.
> This make sense: we are more interested to capture seldom
> values in OLTP that in DW database
>
> Beside Oracle documentation, for more information about the adaptive
> tresholds, you have a good explanation on Asktom=>
>
>
> https://asktom.oracle.com/pls/apex/f?p=100:11:0::::P11_QUESTION_ID:1525205200346930663
>
> Also, I have written a little article about this topic on my blog, this is
> strictly nothing new, but there are 2 pictures that can help the global
> understanding of adaptive tresholds
>
> http://jastrebicdragutin.wordpress.com/2014/11/03/adaptive-tresholds/
>
> HTH
> Dragutin
>
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>
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