Github user rmetzger commented on the issue: https://github.com/apache/flink/pull/3068 Mh, I just realized that the streaming APIs multichaining is leading to some ugly side effects. In below screenshot, you see that the number of outgoing records is reported as 247. These records are the number of elements emitted by the filter. The task below the source is the window that is consuming the data from the filter. Now the next two tasks also consume data from the same task, but without the filter. You can see that they've consumed much more data (because its unfiltered). 
--- If your project is set up for it, you can reply to this email and have your reply appear on GitHub as well. If your project does not have this feature enabled and wishes so, or if the feature is enabled but not working, please contact infrastructure at infrastruct...@apache.org or file a JIRA ticket with INFRA. ---