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https://issues.apache.org/jira/browse/DRILL-5266?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15881190#comment-15881190
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ASF GitHub Bot commented on DRILL-5266:
---------------------------------------
Github user paul-rogers commented on a diff in the pull request:
https://github.com/apache/drill/pull/749#discussion_r102809881
--- Diff:
exec/java-exec/src/main/java/org/apache/drill/exec/store/parquet/columnreaders/ParquetRecordReader.java
---
@@ -73,6 +72,7 @@
private static final long DEFAULT_BATCH_LENGTH = 256 * 1024 *
NUMBER_OF_VECTORS; // 256kb
private static final long DEFAULT_BATCH_LENGTH_IN_BITS =
DEFAULT_BATCH_LENGTH * 8; // 256kb
private static final char DEFAULT_RECORDS_TO_READ_IF_NOT_FIXED_WIDTH =
32*1024;
--- End diff --
Fixed.
> Parquet Reader produces "low density" record batches - bits vs. bytes
> ---------------------------------------------------------------------
>
> Key: DRILL-5266
> URL: https://issues.apache.org/jira/browse/DRILL-5266
> Project: Apache Drill
> Issue Type: Bug
> Components: Storage - Parquet
> Affects Versions: 1.10
> Reporter: Paul Rogers
> Assignee: Paul Rogers
> Labels: ready-to-commit
>
> Testing with the managed sort revealed that, for at least one file, Parquet
> produces "low-density" batches: batches in which only 5% of each value vector
> contains actual data, with the rest being unused space. When fed into the
> sort, we end up buffering 95% of wasted space, using only 5% of available
> memory to hold actual query data. The result is poor performance of the sort
> as it must spill far more frequently than expected.
> The managed sort analyzes incoming batches to prepare good memory use
> estimates. The following the the output from the Parquet file in question:
> {code}
> Actual batch schema & sizes {
> T1¦¦cs_sold_date_sk(std col. size: 4, actual col. size: 4, total size:
> 196608, vector size: 131072, data size: 4516, row capacity: 32768, density: 4)
> T1¦¦cs_sold_time_sk(std col. size: 4, actual col. size: 4, total size:
> 196608, vector size: 131072, data size: 4516, row capacity: 32768, density: 4)
> T1¦¦cs_ship_date_sk(std col. size: 4, actual col. size: 4, total size:
> 196608, vector size: 131072, data size: 4516, row capacity: 32768, density: 4)
> ...
> c_email_address(std col. size: 54, actual col. size: 27, total size: 53248,
> vector size: 49152, data size: 30327, row capacity: 4095, density: 62)
> Records: 1129, Total size: 32006144, Row width:28350, Density:5}
> {code}
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