[
https://issues.apache.org/jira/browse/HIVE-25765?focusedWorklogId=689484&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-689484
]
ASF GitHub Bot logged work on HIVE-25765:
-----------------------------------------
Author: ASF GitHub Bot
Created on: 02/Dec/21 16:51
Start Date: 02/Dec/21 16:51
Worklog Time Spent: 10m
Work Description: ganeshashree opened a new pull request #2838:
URL: https://github.com/apache/hive/pull/2838
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### What changes were proposed in this pull request?
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When skip.header.line.count property is set in table properties, simple
select queries that gets converted into FetchTask skip rows of each block
instead of skipping header lines of each file. This happens when the file size
is larger and file is read in blocks. This issue doesn't exist when select
query is converted into map only job by setting hive.fetch.task.conversion to
none because the header lines are skipped only for the first block because of
[this
check](https://github.com/apache/hive/blob/master/ql/src/java/org/apache/hadoop/hive/ql/io/HiveContextAwareRecordReader.java#L330).
We should have similar check in FetchOperator to avoid this issue.
Ref: https://issues.apache.org/jira/browse/HIVE-25765 for more details.
### Why are the changes needed?
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This change is required to avoid getting incorrect result when simple select
query is converted into FetchTask and the data file size is larger.
### Does this PR introduce _any_ user-facing change?
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the documentation fix.
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No
### How was this patch tested?
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Patch was tested by running simple select queries on a table created on top
of larger data set. Couldn't add qtest since the dataset is larger. Verified
that the numbers rows returned by running aggregation [ count(*) ] and
selecting all columns without limit (select *) are same. Please refer
[HIVE-25765](https://issues.apache.org/jira/browse/HIVE-25765) for the dataset
and queries to test this patch.
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Issue Time Tracking
-------------------
Worklog Id: (was: 689484)
Remaining Estimate: 0h
Time Spent: 10m
> skip.header.line.count property skips rows of each block in FetchOperator
> when file size is larger
> --------------------------------------------------------------------------------------------------
>
> Key: HIVE-25765
> URL: https://issues.apache.org/jira/browse/HIVE-25765
> Project: Hive
> Issue Type: Bug
> Affects Versions: 3.1.2
> Reporter: Ganesha Shreedhara
> Assignee: Ganesha Shreedhara
> Priority: Major
> Labels: pull-request-available
> Attachments: data.txt.gz
>
> Time Spent: 10m
> Remaining Estimate: 0h
>
> When _skip.header.line.count_ property is set in table properties, simple
> select queries that gets converted into FetchTask skip rows of each block
> instead of skipping header lines of each file. This happens when the file
> size is larger and file is read in blocks. This issue doesn't exist when
> select query is converted into map only job by setting
> _hive.fetch.task.conversion_ to _none_ because the header lines are skipped
> only for the first block because of [this
> check|https://github.com/apache/hive/blob/master/ql/src/java/org/apache/hadoop/hive/ql/io/HiveContextAwareRecordReader.java#L330]
> We should have similar check in FetchOperator to avoid this issue.
>
> *Steps to reproduce:*
> {code:java}
> -- Create table on top of the data file (uncompressed size: ~239M) attached
> in this ticket
> CREATE EXTERNAL TABLE test_table(
> col1 string,
> col2 string,
> col3 string,
> col4 string,
> col5 string,
> col6 string,
> col7 string,
> col8 string,
> col9 string,
> col10 string,
> col11 string,
> col12 string)
> ROW FORMAT SERDE
> 'org.apache.hadoop.hive.serde2.lazy.LazySimpleSerDe'
> STORED AS INPUTFORMAT
> 'org.apache.hadoop.mapred.TextInputFormat'
> OUTPUTFORMAT
> 'org.apache.hadoop.hive.ql.io.HiveIgnoreKeyTextOutputFormat'
> LOCATION
> 'location_of_data_file'
> TBLPROPERTIES ('skip.header.line.count'='1');
> -- Counting number of rows gives correct result with only one header line
> skipped
> select count(*) from test_table;
> 3145727
> -- Select query skips more rows and the result depends upon the number of
> blocks configured in underlying filesystem. 3 rows are skipped when the file
> is read in 3 blocks.
> select * from test_table;
> .
> .
> Fetched 3145724 rows
> {code}
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