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https://issues.apache.org/jira/browse/DRILL-4905?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15573621#comment-15573621
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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_r83334623
--- 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 --
I assume numRecordsToRead should be within range of [1, rowCount]. Do we
need enforce such range? What if I pass in 0 or rowCount + 100 ?
> 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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