Hi Bart, if you run a fold function on a keyed stream without a window, there is no way to remove the key and the folded value. You will eventually run out of memory if your key space is continuously growing.
If you apply a fold function in a window on a keyed stream you can bound the "lifetime" of the key and value. Similar as with a non-windowed fold, you can emit a record for each incoming record. Additionally, you can register a timer to purge the window content after a certain time (such as a few days). This blog post should be a good introduction into Flink's window and trigger mechanism [1]. Best, Fabian [1] http://flink.apache.org/news/2015/12/04/Introducing-windows.html 2016-03-18 11:42 GMT+01:00 Bart van Deenen <bartvandee...@fastmail.fm>: > If I do a fold on a KeyedStream, I aggregate events for such-and-such > key. > My question is, what happens with the aggregate (and its key) when > events for this key stop coming? > My keys are browser session keys, and are virtually limitless. > > Ideally, I'd like to send some sort of purge event on keys a couple of > days later, where I empty the aggregate in the fold. That still leaves > the key though, where does that go? > > Any answers highly appreciated... > > Greetings > > Bart >
