[jira] [Commented] (DRILL-4905) Push down the LIMIT to the parquet reader scan to limit the numbers of records read

[ASF GitHub Bot (JIRA)]

    [ 
https://issues.apache.org/jira/browse/DRILL-4905?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15573625#comment-15573625
 ] 

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_r83334160
  
    --- Diff: 
exec/java-exec/src/main/java/org/apache/drill/exec/store/parquet/columnreaders/ParquetRecordReader.java
 ---
    @@ -115,17 +118,30 @@
       public ParquetRecordReader(FragmentContext fragmentContext,
           String path,
           int rowGroupIndex,
    +      long numRecordsToRead,
           FileSystem fs,
           CodecFactory codecFactory,
           ParquetMetadata footer,
           List<SchemaPath> columns) throws ExecutionSetupException {
    -    this(fragmentContext, DEFAULT_BATCH_LENGTH_IN_BITS, path, 
rowGroupIndex, fs, codecFactory, footer,
    -        columns);
    +    this(fragmentContext, DEFAULT_BATCH_LENGTH_IN_BITS, numRecordsToRead,
    +         path, rowGroupIndex, fs, codecFactory, footer, columns);
    +  }
    +
    +  public ParquetRecordReader(FragmentContext fragmentContext,
    +      String path,
    +      int rowGroupIndex,
    +      FileSystem fs,
    +      CodecFactory codecFactory,
    +      ParquetMetadata footer,
    +      List<SchemaPath> columns) throws ExecutionSetupException {
    +      this(fragmentContext, DEFAULT_BATCH_LENGTH_IN_BITS, 
DEFAULT_RECORDS_TO_READ_NOT_SPECIFIED,
    --- End diff --
    
    I think we can get rid of DEFAULT_RECORDS_TO_READ_NOT_SPECIFIED. If  
numRecordsToRead is not specified,  just use rowCount in the row Group. 


> 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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