[jira] [Commented] (SPARK-33206) Spark Shuffle Index Cache calculates memory usage wrong

["Lars Francke (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/SPARK-33206?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17218306#comment-17218306 ] 

Lars Francke commented on SPARK-33206:
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I used YourKit (thank you for the free license!) and it claims that ShuffleIndexInformation uses 152 byte of retained memory when it caches a 0 byte file.

> Spark Shuffle Index Cache calculates memory usage wrong
> -------------------------------------------------------
>
>                 Key: SPARK-33206
>                 URL: https://issues.apache.org/jira/browse/SPARK-33206
>             Project: Spark
>          Issue Type: Bug
>          Components: Shuffle
>    Affects Versions: 2.4.0, 3.0.1
>            Reporter: Lars Francke
>            Priority: Major
>         Attachments: image001(1).png
>
>
> dSPARK-21501 changed the spark shuffle index service to be based on memory instead of the number of files.
> Unfortunately, there's a problem with the calculation which is based on size information provided by `ShuffleIndexInformation`.
> It is based purely on the file size of the cached file on disk.
> We're running in OOMs with very small index files (byte size ~16 bytes) but the overhead of the ShuffleIndexInformation around this is much larger (e.g. 184 bytes, see screenshot). We need to take this into account and should probably add a fixed overhead of somewhere between 152 and 180 bytes according to my tests. I'm not 100% sure what the correct number is and it'll also depend on the architecture etc. so we can't be exact anyway.
> If we do that we can maybe get rid of the size field in ShuffleIndexInformation to save a few more bytes per entry.
> In effect this means that for small files we use up about 70-100 times as much memory as we intend to. Our NodeManagers OOM with 4GB and more of indexShuffleCache.
>  
>  



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