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Posted to issues@beam.apache.org by "ASF GitHub Bot (JIRA)" <ji...@apache.org> on 2018/11/21 22:56:00 UTC
[jira] [Work logged] (BEAM-6110) Beam SQL join moves element
timestamps to EOW sometimes, not always
[ https://issues.apache.org/jira/browse/BEAM-6110?focusedWorklogId=168569&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-168569 ]
ASF GitHub Bot logged work on BEAM-6110:
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Author: ASF GitHub Bot
Created on: 21/Nov/18 22:55
Start Date: 21/Nov/18 22:55
Worklog Time Spent: 10m
Work Description: kennknowles opened a new pull request #7115: [BEAM-6110] For SQL CoGBK-based join use EARLIEST output timestamp
URL: https://github.com/apache/beam/pull/7115
As an implementation detail of some SQL (equi-)joins, we perform a CoGBK. The element timestamps from this are not super important, since the next GROUP BY will have windowing that explicitly says which column to treat as a timestamp. In other words, there is no need for a "timestamp combiner" to decide what the output timestamp is since it is explicit. But we do need the watermark to be held in an appropriate way. If we let it jump to the end of the window and that happens to be the global window, then any downstream windowing will be immediately droppable.
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Issue Time Tracking
-------------------
Worklog Id: (was: 168569)
Time Spent: 10m
Remaining Estimate: 0h
> Beam SQL join moves element timestamps to EOW sometimes, not always
> -------------------------------------------------------------------
>
> Key: BEAM-6110
> URL: https://issues.apache.org/jira/browse/BEAM-6110
> Project: Beam
> Issue Type: Bug
> Components: dsl-sql
> Reporter: Kenneth Knowles
> Assignee: Kenneth Knowles
> Priority: Major
> Time Spent: 10m
> Remaining Estimate: 0h
>
> When a CoGBK join is chosen, element timestamps move to EOW. When side input or lookup join is chosen, element timestamps are the timestamps from the main input element. In SQL sementics, these timestamps are not observable, as windowing is assigned at the next GROUP BY. So we just need the output to hold the watermark so that nothing becomes late or droppable, which implies we need to use MIN timestamp combiner.
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