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https://issues.apache.org/jira/browse/DRILL-5941?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16249774#comment-16249774
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ASF GitHub Bot commented on DRILL-5941:
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Github user arina-ielchiieva commented on the issue:
https://github.com/apache/drill/pull/1030
@ppadma really good point! I did not realize that when creating readers
input splits can be already distributed among several drillbits. So I guess we
should make sure that when we have skip header / footer logic in table input
splits of the same file reside in one `HiveSubScan` during planning stage. I'll
have to make some changes and let you know once done.
> Skip header / footer logic works incorrectly for Hive tables when file has
> several input splits
> -----------------------------------------------------------------------------------------------
>
> Key: DRILL-5941
> URL: https://issues.apache.org/jira/browse/DRILL-5941
> Project: Apache Drill
> Issue Type: Bug
> Components: Storage - Hive
> Affects Versions: 1.11.0
> Reporter: Arina Ielchiieva
> Assignee: Arina Ielchiieva
> Fix For: Future
>
>
> *To reproduce*
> 1. Create csv file with two columns (key, value) for 3000029 rows, where
> first row is a header.
> The data file has size of should be greater than chunk size of 256 MB. Copy
> file to the distributed file system.
> 2. Create table in Hive:
> {noformat}
> CREATE EXTERNAL TABLE `h_table`(
> `key` bigint,
> `value` string)
> ROW FORMAT DELIMITED
> FIELDS TERMINATED BY ','
> STORED AS INPUTFORMAT
> 'org.apache.hadoop.mapred.TextInputFormat'
> OUTPUTFORMAT
> 'org.apache.hadoop.hive.ql.io.HiveIgnoreKeyTextOutputFormat'
> LOCATION
> 'maprfs:/tmp/h_table'
> TBLPROPERTIES (
> 'skip.header.line.count'='1');
> {noformat}
> 3. Execute query {{select * from hive.h_table}} in Drill (query data using
> Hive plugin). The result will return less rows then expected. Expected result
> is 3000028 (total count minus one row as header).
> *The root cause*
> Since file is greater than default chunk size, it's split into several
> fragments, known as input splits. For example:
> {noformat}
> maprfs:/tmp/h_table/h_table.csv:0+268435456
> maprfs:/tmp/h_table/h_table.csv:268435457+492782112
> {noformat}
> TextHiveReader is responsible for handling skip header and / or footer logic.
> Currently Drill creates reader [for each input
> split|https://github.com/apache/drill/blob/master/contrib/storage-hive/core/src/main/java/org/apache/drill/exec/store/hive/HiveScanBatchCreator.java#L84]
> and skip header and /or footer logic is applied for each input splits,
> though ideally the above mentioned input splits should have been read by one
> reader, so skip / header footer logic was applied correctly.
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