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https://issues.apache.org/jira/browse/SPARK-30866?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Dongjoon Hyun resolved SPARK-30866.
-----------------------------------
    Fix Version/s: 3.1.0
       Resolution: Fixed

Issue resolved by pull request 27620
[https://github.com/apache/spark/pull/27620]

> FileStreamSource: Cache fetched list of files beyond maxFilesPerTrigger as 
> unread files
> ---------------------------------------------------------------------------------------
>
>                 Key: SPARK-30866
>                 URL: https://issues.apache.org/jira/browse/SPARK-30866
>             Project: Spark
>          Issue Type: Improvement
>          Components: Structured Streaming
>    Affects Versions: 3.1.0
>            Reporter: Jungtaek Lim
>            Assignee: Jungtaek Lim
>            Priority: Major
>             Fix For: 3.1.0
>
>
> FileStreamSource fetches the available files per batch which is a "heavy 
> cost" operation.
> (E.g. It took around 5 seconds to list leaf files for 95 paths which contain 
> 674,811 files. It's not even in HDFS path - it's local filesystem.)
> If "maxFilesPerTrigger" is not set, Spark would consume all the fetched 
> files. After the batch has been completed, it's obvious for Spark to fetch 
> per micro batch.
> If "latestFirst" is true (regardless of "maxFilesPerTrigger"), the files to 
> process should be updated per batch, so it's also obvious for Spark to fetch 
> per micro batch.
> Except above cases (in short, maxFilesPerTrigger is being set and latestFirst 
> is false), the files to process can be "continuous" - we can "cache" the 
> fetched list of files and consume until the list has been exhausted.



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