[jira] [Commented] (PARQUET-2443) Support lazy materialization of row groups in ParquetFileReader

["Claire McGinty (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/PARQUET-2443?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17823759#comment-17823759 ] 

Claire McGinty commented on PARQUET-2443:
-----------------------------------------

I pushed a branch implementing the DataPage-as-Iterator idea, here: [https://github.com/apache/parquet-mr/compare/master...clairemcginty:parquet-mr:lazy-chunkreader]

 

However... it looks like ColumnReaderBase#checkRead works by continually invoking `readPage` [until the row group is fully consumed|https://github.com/apache/parquet-mr/blob/master/parquet-column/src/main/java/org/apache/parquet/column/impl/ColumnReaderBase.java#L653-L676], so the row group effectively gets materialized there. Any pointers on how I should modify that code block? 

> Support lazy materialization of row groups in ParquetFileReader
> ---------------------------------------------------------------
>
>                 Key: PARQUET-2443
>                 URL: https://issues.apache.org/jira/browse/PARQUET-2443
>             Project: Parquet
>          Issue Type: Improvement
>            Reporter: Claire McGinty
>            Priority: Major
>
> Motivation: The current behavior of ParquetFilterReader#readNextRowGroup is to eagerly enumerate all chunks in the row group, then read all pages in the chunk. For distributed data workloads, this can cause significant memory pressure, particularly for use cases that require the colocation of multiple Parquet files on a single worker.
>  
> Proposal: A Parquet Configuration option that enables lazy row group reading, i.e., only a page at a time (plus whatever header is necessary to read that header). The Configuration option could be either a flag, or an int value for how many pages/page bytes to buffer at a time.
>  
> I think this could be accomplished by modifying [ParquetFileReader#readAllPages|https://github.com/apache/parquet-mr/blob/cf294a35ca4b635f44357fe4c170f3b66870dc6e/parquet-hadoop/src/main/java/org/apache/parquet/hadoop/ParquetFileReader.java#L1727] to re-implement pagesInChunk as an Iterator<DataPage>, rather than a List<DataPage>. Then, ColumnChunkPageReader could parse the Configuration option above and decide whether to fully materialize the iterator or not.
>  
> I'm happy to try to create a draft/branch for this to get some early feedback on the idea!



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