[jira] [Resolved] (SPARK-22552) Cannot Union multiple kafka streams

["sachin malhotra (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/SPARK-22552?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

sachin malhotra resolved SPARK-22552.
-------------------------------------
    Resolution: Not A Problem

> Cannot Union multiple kafka streams
> -----------------------------------
>
>                 Key: SPARK-22552
>                 URL: https://issues.apache.org/jira/browse/SPARK-22552
>             Project: Spark
>          Issue Type: Bug
>          Components: Structured Streaming
>    Affects Versions: 2.2.0
>            Reporter: sachin malhotra
>            Priority: Minor
>
> When unioning multiple kafka streams I learned that the resulting dataframe only contains the data that exists in the dataframe that initiated the union i.e. if df1.union(df2) (or a chaining of unions) the result will only contain the rows that exist in df1.
> Now to be more specific this occurs when data comes in during the same micro-batch for all three streams. If you wait for each single row to be processed for each stream the union does return the right results. 
> For example, if you have 3 kafka streams and you:
> send message 1 to stream 1, WAIT for batch to finish, send message 2 to stream 2, wait for batch to finish, send message 3 to stream 3, wait for batch to finish. Union will return the right data.
> But if you,
> send message 1,2,3, WAIT for batch to finish, you only receive data in the first stream when unioning all three dataframes



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