Hi, the Evictor is very tricky to understand, I’m afraid. What happens when a Trigger fires is the following: 1. Trigger fires 2. Evictor can remove elements from the window buffer 3. Window function processes the elements that remain in the window buffer
The tricky thing here is that the Evictor should really be called “Keeper”. What it does in fact is specify how many elements should be kept in the buffer. For example, an Evictor “CountEvict(5)” means, keep 5 elements, a “TimeEvictor(5 minutes)” keeps the elements that a younger than 5 minutes. I admit this is somewhat counterintuitive but this is how the policies work in IBM Infosphere Streams and they influenced the early design of the Flink Trigger/Eviction policies. (See here for a description of the semantics of IBM Infosphere Streams: http://www.cs.bilkent.edu.tr/~bgedik/homepage/lib/exe/fetch.php/wiki:pubs:windowing.pdf) If it is still unclear, could you please but together a working example where the behavior is unclear to you so that we can have a look at it. Cheers, Aljoscha > On 30 Nov 2015, at 12:08, Nirmalya Sengupta <sengupta.nirma...@gmail.com> > wrote: > > Hi Aljoscha <aljos...@apache.org>, > > Thanks for taking interest in my post and question. > > If the Evictor removes elements _before_ the function is applied, then what > happens the first time, the Evictor is acting? That's what I am failing to > understand. At the beginning of the operation on the Stream, he Trigger finds > 5 elements, the Evictor removes 2 of them (let's say), and Sum sees incorrect > number of elements. Isn't this possible or again, am I demonstrating my loose > grasp of the matter? > > Please correct me. > > -- N > > > -- > 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."
