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https://issues.apache.org/jira/browse/HIVE-2121?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13025498#comment-13025498
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jirapos...@reviews.apache.org commented on HIVE-2121:
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trunk/ql/src/java/org/apache/hadoop/hive/ql/io/CombineHiveInputFormat.java
<https://reviews.apache.org/r/633/#comment1205>

    This function could be quite expensive inside the loops. You may want to 
test a case where there are large # of partitions and each partition contains a 
large # of small files. 


- Ning


On 2011-04-26 21:19:18, Siying Dong wrote:
bq.  
bq.  -----------------------------------------------------------
bq.  This is an automatically generated e-mail. To reply, visit:
bq.  https://reviews.apache.org/r/633/
bq.  -----------------------------------------------------------
bq.  
bq.  (Updated 2011-04-26 21:19:18)
bq.  
bq.  
bq.  Review request for hive, Ning Zhang and namit jain.
bq.  
bq.  
bq.  Summary
bq.  -------
bq.  
bq.  We need a better input sampling to serve at least two purposes:
bq.  1. test their queries against a smaller data set
bq.  2. understand more about how the data look like without scanning the whole 
table.
bq.  A simple function that gives a subset splits will help in those cases. It 
doesn't have to be strict sampling.
bq.  
bq.  This diff allows a syntax of .. table TABLESAMPLE(n PERCENT), which 
samples input splits with size at least n% of the original inputs.
bq.  
bq.  
bq.  This addresses bug HIVE-2121.
bq.      https://issues.apache.org/jira/browse/HIVE-2121
bq.  
bq.  
bq.  Diffs
bq.  -----
bq.  
bq.    trunk/common/src/java/org/apache/hadoop/hive/conf/HiveConf.java 1096852 
bq.    trunk/conf/hive-default.xml 1096852 
bq.    
trunk/ql/src/java/org/apache/hadoop/hive/ql/io/CombineHiveInputFormat.java 
1096852 
bq.    trunk/ql/src/java/org/apache/hadoop/hive/ql/io/HiveFileFormatUtils.java 
1096852 
bq.    
trunk/ql/src/java/org/apache/hadoop/hive/ql/optimizer/GenMRFileSink1.java 
1096852 
bq.    
trunk/ql/src/java/org/apache/hadoop/hive/ql/optimizer/GenMRTableScan1.java 
1096852 
bq.    trunk/ql/src/java/org/apache/hadoop/hive/ql/optimizer/GenMRUnion1.java 
1096852 
bq.    
trunk/ql/src/java/org/apache/hadoop/hive/ql/optimizer/GenMapRedUtils.java 
1096852 
bq.    
trunk/ql/src/java/org/apache/hadoop/hive/ql/optimizer/MapJoinFactory.java 
1096852 
bq.    trunk/ql/src/java/org/apache/hadoop/hive/ql/parse/Hive.g 1096852 
bq.    trunk/ql/src/java/org/apache/hadoop/hive/ql/parse/ParseContext.java 
1096852 
bq.    trunk/ql/src/java/org/apache/hadoop/hive/ql/parse/SemanticAnalyzer.java 
1096852 
bq.    trunk/ql/src/java/org/apache/hadoop/hive/ql/parse/SplitSample.java 
PRE-CREATION 
bq.    trunk/ql/src/java/org/apache/hadoop/hive/ql/plan/MapredWork.java 1096852 
bq.    trunk/ql/src/test/queries/clientnegative/split_sample_disabled.q 
PRE-CREATION 
bq.    trunk/ql/src/test/queries/clientnegative/split_sample_out_of_range.q 
PRE-CREATION 
bq.    trunk/ql/src/test/queries/clientnegative/split_sample_wrong_format.q 
PRE-CREATION 
bq.    trunk/ql/src/test/queries/clientpositive/split_sample.q PRE-CREATION 
bq.    trunk/ql/src/test/results/clientnegative/split_sample_disabled.q.out 
PRE-CREATION 
bq.    trunk/ql/src/test/results/clientnegative/split_sample_out_of_range.q.out 
PRE-CREATION 
bq.    trunk/ql/src/test/results/clientnegative/split_sample_wrong_format.q.out 
PRE-CREATION 
bq.    trunk/ql/src/test/results/clientpositive/bucket1.q.out 1096852 
bq.    trunk/ql/src/test/results/clientpositive/bucket2.q.out 1096852 
bq.    trunk/ql/src/test/results/clientpositive/bucket3.q.out 1096852 
bq.    trunk/ql/src/test/results/clientpositive/bucketmapjoin1.q.out 1096852 
bq.    trunk/ql/src/test/results/clientpositive/sample1.q.out 1096852 
bq.    trunk/ql/src/test/results/clientpositive/sample10.q.out 1096852 
bq.    trunk/ql/src/test/results/clientpositive/sample2.q.out 1096852 
bq.    trunk/ql/src/test/results/clientpositive/sample3.q.out 1096852 
bq.    trunk/ql/src/test/results/clientpositive/sample4.q.out 1096852 
bq.    trunk/ql/src/test/results/clientpositive/sample5.q.out 1096852 
bq.    trunk/ql/src/test/results/clientpositive/sample6.q.out 1096852 
bq.    trunk/ql/src/test/results/clientpositive/sample7.q.out 1096852 
bq.    trunk/ql/src/test/results/clientpositive/sample8.q.out 1096852 
bq.    trunk/ql/src/test/results/clientpositive/sample9.q.out 1096852 
bq.  
bq.  Diff: https://reviews.apache.org/r/633/diff
bq.  
bq.  
bq.  Testing
bq.  -------
bq.  
bq.  TestCliDriver TestNegativeCliDriver, manual tests on real clusters.
bq.  
bq.  
bq.  Thanks,
bq.  
bq.  Siying
bq.  
bq.



> Input Sampling By Splits
> ------------------------
>
>                 Key: HIVE-2121
>                 URL: https://issues.apache.org/jira/browse/HIVE-2121
>             Project: Hive
>          Issue Type: New Feature
>            Reporter: Siying Dong
>            Assignee: Siying Dong
>         Attachments: HIVE-2121.1.patch, HIVE-2121.2.patch, HIVE-2121.3.patch
>
>
> We need a better input sampling to serve at least two purposes:
> 1. test their queries against a smaller data set
> 2. understand more about how the data look like without scanning the whole 
> table.
> A simple function that gives a subset splits will help in those cases. It 
> doesn't have to be strict sampling.

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