TimeWindow causes crazy results

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flp
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TimeWindow causes crazy results

Post by flp » Mon Oct 27, 2014 1:24 am

https://www.dropbox.com/sh/q8a269fq3437 ... Q9yka?dl=0

If I run the Task1 query without time window, I receive normal values.
If I include the time window, the aggregation seems to decrease the values after a while.

Do you have any clue why this happens?

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Marco Grawunder
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Re: TimeWindow causes crazy results

Post by Marco Grawunder » Mon Oct 27, 2014 10:05 am

I think, this could be the normal behaviour. See

http://wiki.odysseus.offis.uni-oldenbur ... and+Window

for explanation of windows and aggregations.

flp
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Re: TimeWindow causes crazy results

Post by flp » Mon Oct 27, 2014 1:19 pm

I want to aggregate all values over the whole time. And as I thought I need to have a window for aggregations to avoid memory overflows.
So I can't use windows for my query?

Furthermore, the description tells that it will start a new aggregation, but it does not start to decrease the values.

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Marco Grawunder
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Re: TimeWindow causes crazy results

Post by Marco Grawunder » Mon Oct 27, 2014 2:16 pm

If you want to aggregate all values, a window cannot reduce memory usage ;-)

One important thing in Odysseus: All elements have valid times (start and optional end timestamps). They are defined, when a new tuple arrives the system by setting the timestamp by an attribute (STARTTIMESTAMP) or by arrival time. Elements are only put together, if these valid times overlapp. When using a window with slide parameter (instead of the width), elements are given the same starttimestamp in each window.

What do you mean with "decrease the values"?

flp
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Re: TimeWindow causes crazy results

Post by flp » Mon Oct 27, 2014 6:12 pm

When I use the last elements (time) view, the values start decreasing after a while, while it doesn't happen without windows. It seems for me that instead of adding the values are somehow subtracted. It's a feeling, I can't really proof that.

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Marco Grawunder
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Re: TimeWindow causes crazy results

Post by Marco Grawunder » Mon Oct 27, 2014 6:22 pm

I assume, that the values are no longer valid.

When you have the following elements. Becoming valid at 0,5, 10 and 15 and stay valid forever

1 [0,oo]
1 [5,oo]
1 [10,oo]
1 [15,oo]

the output e.g. for a count would be
1 [0,5]
2 [5,10]
3 [10,15]
and after stopping the query
4 [15,oo]

When using a time window with size 10, the values will (after the window) look like:

1 [0,10]
1 [5,15]
1 [10,20]
1 [15,25]

and the aggregations will be:
1 [0,5] from first [0,5]
2 [5,10] from first [5,10] and second [5,10]
2 [10,15] from second and third
2 [15,20] from third and fourth
1 [20,25] from fourth

So in the last aggregation only the fourth value ist valid and the value decreases.

Hope that this make more clear, that you feeling correspond to a semantically correct processing :-)[

flp
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Joined: Tue Sep 02, 2014 12:54 am

Re: TimeWindow causes crazy results

Post by flp » Mon Oct 27, 2014 11:34 pm

Thank you for clarification. I learned something new today :)

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