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From Kostas Kloudas <k.klou...@data-artisans.com>
Subject Re: maximum size of window
Date Mon, 27 Jun 2016 22:19:12 GMT
Hi Vishnu,

I hope the following will help answer your question:

1) Elements are first split by key (apart from global windows) and then are put into windows.
In other words, windows are keyed.
2) A window belonging to a certain key is handled by a single node. In other words, no matter
how big the window is, its
	state (the elements it contains) will never be split between two or more nodes. 
3) Where the state is stored, depends on your state backend. Currently Flink supports an in-memory
one, a filesystem one, and
	a rocksDB one which is in the middle (first in-memory and then disk when needed). Of course
you can implement your own.

From the above, you can see that if you use the memory-backed state backend, then your window
size is limited by the memory 
available at each of your nodes. If you use the fs state backend, then your state is stored
on disk. Finally, rocksDB will initially 
use RAM and then spill on disk when no more memory is available.

Here I have to add that the window documentation is currently being re-written to explain
new features introduced in Flink 1.1,
which include more flexible handling of late events and more explicit state garbage collection.


So please stay tuned!

I hope this helps at answering your question,
Kostas

> On Jun 27, 2016, at 8:22 PM, Vishnu Viswanath <vishnu.viswanath25@gmail.com> wrote:
> 
> Hi All,
> 
> - Is there any restriction on the size of a window in Flink with respect to the memory
of the nodes?
> - What happens if a window size grows more than size of a node, will it be split into
multiple nodes?
> 
> if I am going to have a huge window, should I have fewer nodes with more memory. 
> Is there any documentation on how memory is managed/handled in the case of windows and
also in the case of joins.
> 
> Regards,
> Vishnu


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