[jira] [Commented] (PARQUET-1982) Allow random access to row groups in ParquetFileReader

["ASF GitHub Bot (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/PARQUET-1982?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17286443#comment-17286443 ] 

ASF GitHub Bot commented on PARQUET-1982:
-----------------------------------------

fschmalzel opened a new pull request #871:
URL: https://github.com/apache/parquet-mr/pull/871


   Adds a method readRowGroup(BlockMetaData) to allow random access to
   PageReadStores via BlockMetaData, which can be obtained using the
   getRowGroups() method.
   
   This is similar to the existing method
   getDictionaryReader(BlockMetaData)
   that already exists.
   
   With random access the reader can be reused if for example someone
   needs to go back a row group. This would improve performance
   because we don't need to open the file again and read the metadata.
   
   Make sure you have checked _all_ steps below.
   
   ### Jira
   
   - [x ] My PR addresses the following [Parquet Jira](https://issues.apache.org/jira/browse/PARQUET-1982) issue.
   
   ### Tests
   
   - [x ] My PR adds the following unit tests:
    - TestParquetReaderRandomAccess
   
   ### Commits
   
   - [x ] My commits all reference Jira issues in their subject lines. In addition, my commits follow the guidelines from "[How to write a good git commit message](http://chris.beams.io/posts/git-commit/)":
     1. Subject is separated from body by a blank line
     1. Subject is limited to 50 characters (not including Jira issue reference)
     1. Subject does not end with a period
     1. Subject uses the imperative mood ("add", not "adding")
     1. Body wraps at 72 characters
     1. Body explains "what" and "why", not "how"
   
   ### Documentation
   
   - [x ] In case of new functionality, my PR adds documentation that describes how to use it.
     - All the public functions and the classes in the PR contain Javadoc that explain what it does
   


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> Allow random access to row groups in ParquetFileReader
> ------------------------------------------------------
>
>                 Key: PARQUET-1982
>                 URL: https://issues.apache.org/jira/browse/PARQUET-1982
>             Project: Parquet
>          Issue Type: New Feature
>          Components: parquet-mr
>            Reporter: Felix Schmalzel
>            Priority: Minor
>              Labels: parquetReader, random-access
>
> The used SeekableInputStream and all other components of the ParquetFileReader already support random access and row groups should be independent of each other.
> This would allow reusing the opened InputStream when you want to go back a row group. It also makes accessing specific row groups a lot easier.
> I've already developed a patch that would enable this functionality. I will link the merge request in the next few days.
> Is there a related ticket that i have overlooked?



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