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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 Tue, 18 Oct 2016 22:32:59 GMT

    [ https://issues.apache.org/jira/browse/DRILL-4905?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15586882#comment-15586882
] 

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

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

    https://github.com/apache/drill/pull/597#discussion_r83965017
  
    --- Diff: exec/java-exec/src/main/java/org/apache/drill/exec/store/parquet/columnreaders/ParquetRecordReader.java
---
    @@ -139,6 +155,11 @@ public ParquetRecordReader(
         this.batchSize = batchSize;
         this.footer = footer;
         this.fragmentContext = fragmentContext;
    +    if (numRecordsToRead == DEFAULT_RECORDS_TO_READ_NOT_SPECIFIED) {
    +      this.numRecordsToRead =  footer.getBlocks().get(rowGroupIndex).getRowCount();
    +    } else {
    +      this.numRecordsToRead = numRecordsToRead;
    --- End diff --
    
    Current code handles if numRecordsToRead is not in the range.  So, I am not adding additional
checks here. 


> 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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