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Posted to issues@hive.apache.org by "ASF GitHub Bot (Jira)" <ji...@apache.org> on 2021/12/02 16:52:00 UTC
[jira] [Work logged] (HIVE-25765) skip.header.line.count property skips rows of each block in FetchOperator when file size is larger
[ 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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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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