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https://issues.apache.org/jira/browse/HIVE-22495?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Jason Xu updated HIVE-22495:
----------------------------
Description:
Running a hive query on a Parquet table
select count ( * ) from t
The query read in all data (all columns) instead of just metadata.
For comparison, hive 0.13 and Spark read in much less data.
||engine||HDFS data read||
|Hive| 452.9 MB|
|Hive 0.13| 22.5 KB|
|Spark| 41.6 KB|
Seems cause is that Parquet read support fall back to file schema if
indexColumnsWanted is empty, logic still exist in master branch.
was:
Running a hive query on a Parquet table
select count ( * ) from t
The query read in all data (all columns) instead of just metadata.
For comparison, hive 0.13 and Spark read in much less data.
||engine||HDFS data read||
|Hive 2.3.4| 452.9 MB|
|Hive 0.13| 22.5 KB|
|Spark| 41.6 KB|
Seems cause is that Parquet read support fall back to file schema if
indexColumnsWanted is empty.
> Parquet count(*) read in all data
> ---------------------------------
>
> Key: HIVE-22495
> URL: https://issues.apache.org/jira/browse/HIVE-22495
> Project: Hive
> Issue Type: Bug
> Components: Reader
> Affects Versions: 2.3.4
> Reporter: Jason Xu
> Assignee: Jason Xu
> Priority: Major
>
> Running a hive query on a Parquet table
> select count ( * ) from t
> The query read in all data (all columns) instead of just metadata.
> For comparison, hive 0.13 and Spark read in much less data.
>
> ||engine||HDFS data read||
> |Hive| 452.9 MB|
> |Hive 0.13| 22.5 KB|
> |Spark| 41.6 KB|
>
> Seems cause is that Parquet read support fall back to file schema if
> indexColumnsWanted is empty, logic still exist in master branch.
>
>
>
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