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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DRILL-4905) Push down the LIMIT to the parquet reader scan to limit the numbers of records read
Date Wed, 28 Sep 2016 17:12:20 GMT

    [ https://issues.apache.org/jira/browse/DRILL-4905?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15530259#comment-15530259
] 

ASF GitHub Bot commented on DRILL-4905:
---------------------------------------

Github user jinfengni commented on a diff in the pull request:

    https://github.com/apache/drill/pull/597#discussion_r80968936
  
    --- Diff: exec/java-exec/src/main/java/org/apache/drill/exec/ExecConstants.java ---
    @@ -125,13 +125,14 @@
       String PARQUET_WRITER_ENABLE_DICTIONARY_ENCODING = "store.parquet.enable_dictionary_encoding";
       OptionValidator PARQUET_WRITER_ENABLE_DICTIONARY_ENCODING_VALIDATOR = new BooleanValidator(
           PARQUET_WRITER_ENABLE_DICTIONARY_ENCODING, false);
    -
       String PARQUET_VECTOR_FILL_THRESHOLD = "store.parquet.vector_fill_threshold";
       OptionValidator PARQUET_VECTOR_FILL_THRESHOLD_VALIDATOR = new PositiveLongValidator(PARQUET_VECTOR_FILL_THRESHOLD,
99l, 85l);
       String PARQUET_VECTOR_FILL_CHECK_THRESHOLD = "store.parquet.vector_fill_check_threshold";
       OptionValidator PARQUET_VECTOR_FILL_CHECK_THRESHOLD_VALIDATOR = new PositiveLongValidator(PARQUET_VECTOR_FILL_CHECK_THRESHOLD,
100l, 10l);
       String PARQUET_NEW_RECORD_READER = "store.parquet.use_new_reader";
       OptionValidator PARQUET_RECORD_READER_IMPLEMENTATION_VALIDATOR = new BooleanValidator(PARQUET_NEW_RECORD_READER,
false);
    +  String PARQUET_RECORD_BATCH_SIZE = "store.parquet.record_batch_size";
    --- End diff --
    
    It would be nice to use "store.parquet.reader.record_batch_size", since this option is
for reader only, not for parquet writer.  We could not change the option name once it's released.

    



> Push down the LIMIT to the parquet reader scan to limit the numbers of records read
> -----------------------------------------------------------------------------------
>
>                 Key: DRILL-4905
>                 URL: https://issues.apache.org/jira/browse/DRILL-4905
>             Project: Apache Drill
>          Issue Type: Bug
>          Components: Storage - Parquet
>    Affects Versions: 1.8.0
>            Reporter: Padma Penumarthy
>            Assignee: Padma Penumarthy
>             Fix For: 1.9.0
>
>
> Limit the number of records read from disk by pushing down the limit to parquet reader.
> For queries like
> select * from <table> limit N; 
> where N < size of Parquet row group, we are reading 32K/64k rows or entire row group.
This needs to be optimized to read only N rows.
>  



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