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https://issues.apache.org/jira/browse/DRILL-4905?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15526881#comment-15526881
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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_r80751189
--- Diff:
exec/java-exec/src/main/java/org/apache/drill/exec/store/parquet/ParquetGroupScan.java
---
@@ -115,6 +115,8 @@
private List<RowGroupInfo> rowGroupInfos;
private Metadata.ParquetTableMetadataBase parquetTableMetadata = null;
private String cacheFileRoot = null;
+ private int batchSize;
+ private static final int DEFAULT_BATCH_LENGTH = 256 * 1024;
--- End diff --
The default batch length is used here to compare with the limit value and
decide if we want to create new groupscan. New option has nothing to do with
this. For normal case, we do not touch/use the option. It is added so we can
use it if we want to change it at run time for any reason.
> 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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