[jira] [Commented] (BEAM-184) Using Merging Windows and/or Triggers without a downstream aggregation should fail

["Kenneth Knowles (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/BEAM-184?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15237500#comment-15237500 ] 

Kenneth Knowles commented on BEAM-184:
--------------------------------------

I agree, for the short term. Long term, at least 1 & 3 should be automated. If the user wants merging windows and their pipeline doesn't have a convenient GBK for us to do it, insert merging (such as GBK+explode) at an opportune location, such as just before they access windows or write to a sink.

Number 2 is a interesting discussion:

* From one perspective, triggering is about getting output from a grouping operation. This suggests either your approach (error if no grouping operation, since it makes no sense) or actually specifying triggering on the grouping operation directly.
* From another perspective, triggering is about limiting output. In streaming, if one has a sound discarding/accumulating/retracting setup, an aggregation can be updated after each input element. Triggers serve to suppress this default flow. This suggests inserting buffering and allowing multiple-element trigger firings. It is much further from today's model.

> Using Merging Windows and/or Triggers without a downstream aggregation should fail
> ----------------------------------------------------------------------------------
>
>                 Key: BEAM-184
>                 URL: https://issues.apache.org/jira/browse/BEAM-184
>             Project: Beam
>          Issue Type: Bug
>          Components: sdk-java-core
>            Reporter: Ben Chambers
>            Priority: Minor
>
> Both merging windows (such as sessions) and triggering only actually happen at an aggregation (GroupByKey). We should produce errors in any of these cases:
> 1. Merging window used without a downstream GroupByKey
> 2. Triggers used without a downstream GroupuByKey
> 3. Window inspected after inserting a merging window and before the GroupByKey



--
This message was sent by Atlassian JIRA
(v6.3.4#6332)