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https://issues.apache.org/jira/browse/HIVE-25827?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17554048#comment-17554048
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Ádám Szita commented on HIVE-25827:
-----------------------------------
We don't need multiple splits of the same file for this to happen. Every file
is opened 2 times with the vectorized reader. And yes, e.g. in LLAP's case
that's two different streams as in that scenario there's a custom logic to load
the metadata part of the file into metadata cache. If there's a cache hit, 1 of
the reads would be served from cache, but the other occasion reads from file in
the dumb way nevertheless.
> Parquet file footer is read multiple times, when multiple splits are created
> in same file
> -----------------------------------------------------------------------------------------
>
> Key: HIVE-25827
> URL: https://issues.apache.org/jira/browse/HIVE-25827
> Project: Hive
> Issue Type: Improvement
> Reporter: Rajesh Balamohan
> Assignee: Ádám Szita
> Priority: Major
> Labels: performance
> Attachments: image-2021-12-21-03-19-38-577.png
>
>
> With large files, it is possible that multiple splits are created in the same
> file. With current codebase, "ParquetRecordReaderBase" ends up reading file
> footer for each split.
> It can be optimized not to read footer information multiple times for the
> same file.
>
> [https://github.com/apache/hive/blob/master/ql/src/java/org/apache/hadoop/hive/ql/io/parquet/vector/VectorizedParquetRecordReader.java#L160]
>
> [https://github.com/apache/hive/blob/master/ql/src/java/org/apache/hadoop/hive/ql/io/parquet/ParquetRecordReaderBase.java#L91]
>
>
> !image-2021-12-21-03-19-38-577.png|width=1363,height=1256!
>
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