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Date: Sat, 28 Nov 2015 07:44:34 +0530
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 <CAEr=Az0qgAc4nfB29QpNY-1y-4GxMr+w9potqfNw2wed=ss5wA@mail.gmail.com>
Subject: Re: Interpretation of Trigger and Eviction on a window
From: Nirmalya Sengupta <sengupta.nirmalya@gmail.com>
To: user@flink.apache.org
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Hello Fabian,

>From your reply to this thread:
' it is correct that the evictor is called BEFORE the window function is
applied because this is required to support certain types of sliding
windows. '

This is clear to me now. However, my point was about the way it is
described in the User-guide. The guide says this:
' *After the trigger fires, and before the function (e.g., sum, count) is
applied to the window contents, an optional Evictor removes some elements
from the beginning of the window before the remaining elements are passed
on to the function* '

As I read it again, I see where the problem lies. It says some elements are
removed before the **rest** are passed to the function. This is not what
happens, I think. Evictor removes elements and the function *sees this set
of removed elements, not the remaining elements*. Remaining elements remain
in the window and are perhaps picked up by the Evictor next time.

Carrying on from your elaboration, I think guide's statement can be better
rearranged as:

' *After the trigger fires, the function (e.g., sum, count) is applied to
the entire contents of the window. However, an optionally
provided Evictor, removes some elements from the beginning of the window,
according to the criteria of eviction. The function is then applied to this
set of __removed__ elements. '*

Let me know if I am way off the mark here.

-- Nirmalya

-- 
Software Technologist
http://www.linkedin.com/in/nirmalyasengupta
"If you have built castles in the air, your work need not be lost. That is
where they should be.
Now put the foundation under them."

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<div dir=3D"ltr"><font face=3D"monospace, monospace">Hello Fabian,</font><d=
iv><font face=3D"monospace, monospace"><br></font></div><div><font face=3D"=
monospace, monospace">From your reply to this thread:=C2=A0</font></div><di=
v><font face=3D"monospace, monospace">&#39;=C2=A0it is correct that the evi=
ctor is called BEFORE the window function is applied because this is requir=
ed to support certain types of sliding windows.=C2=A0&#39;</font></div><div=
><font face=3D"monospace, monospace"><br></font></div><div><font face=3D"mo=
nospace, monospace">This is clear to me now. However, my point was about th=
e way it is described in the User-guide. The guide says this:</font></div><=
div><font face=3D"monospace, monospace">&#39;=C2=A0<i><font color=3D"#3d85c=
6"><span style=3D"line-height:20px">After the trigger fires, and before the=
 function (e.g.,=C2=A0</span><code style=3D"padding:0px;border-radius:4px;b=
ackground:rgb(245,245,245)">sum</code><span style=3D"line-height:20px">,=C2=
=A0</span><code style=3D"padding:0px;border-radius:4px;background:rgb(245,2=
45,245)">count</code><span style=3D"line-height:20px">) is applied to the w=
indow contents, an optional=C2=A0</span><code style=3D"padding:0px;border-r=
adius:4px;background:rgb(245,245,245)">Evictor</code><span style=3D"line-he=
ight:20px">=C2=A0removes some elements from the beginning of the window bef=
ore the remaining elements are passed on to the function</span></font></i>=
=C2=A0&#39;</font></div><div><font face=3D"monospace, monospace"><br></font=
></div><div><font face=3D"monospace, monospace">As I read it again, I see w=
here the problem lies. It says some elements are removed before the **rest*=
* are passed to the function. This is not what happens, I think. Evictor re=
moves elements and the function <b>sees this set of removed elements, not t=
he remaining elements</b>. Remaining elements remain in the window and are =
perhaps picked up by the Evictor next time.</font></div><div><font face=3D"=
monospace, monospace"><br></font></div><div><font face=3D"monospace, monosp=
ace">Carrying on from your elaboration, I think guide&#39;s statement can b=
e better rearranged as:</font></div><div><font face=3D"monospace, monospace=
"><br></font></div><div><font face=3D"monospace, monospace">&#39;=C2=A0<i><=
font color=3D"#3d85c6"><span style=3D"line-height:20px">After the trigger f=
ires, the function (e.g.,=C2=A0</span><code style=3D"padding:0px;border-rad=
ius:4px;background:rgb(245,245,245)">sum</code><span style=3D"line-height:2=
0px">,=C2=A0</span><code style=3D"padding:0px;border-radius:4px;background:=
rgb(245,245,245)">count</code><span style=3D"line-height:20px">) is applied=
 to the entire contents of the window. However, an optionally provided=C2=
=A0</span><code style=3D"padding:0px;border-radius:4px;background:rgb(245,2=
45,245)">Evictor,=C2=A0</code><span style=3D"line-height:20px">removes some=
 elements from the beginning of the window, according to the criteria of ev=
iction. The function is then applied to this set of __removed__ elements.</=
span></font><span style=3D"color:rgb(51,51,51);line-height:20px"> &#39;</sp=
an></i></font></div><div><div><font face=3D"monospace, monospace">=C2=A0</f=
ont></div><div><font face=3D"monospace, monospace">Let me know if I am way =
off the mark here.</font></div><div><font face=3D"monospace, monospace"><br=
></font></div><div><font face=3D"monospace, monospace">-- Nirmalya</font></=
div><div><br></div>-- <br><div>Software Technologist<br><a href=3D"http://w=
ww.linkedin.com/in/nirmalyasengupta" target=3D"_blank">http://www.linkedin.=
com/in/nirmalyasengupta</a><br>&quot;If you have built castles in the air, =
your work need not be lost. That is where they should be.<br>Now put the fo=
undation under them.&quot;</div>
</div></div>

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