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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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