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From "jiraposter@reviews.apache.org (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HIVE-2121) Input Sampling By Splits
Date Tue, 26 Apr 2011 20:53:03 GMT

    [ https://issues.apache.org/jira/browse/HIVE-2121?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13025426#comment-13025426
] 

jiraposter@reviews.apache.org commented on HIVE-2121:
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-----------------------------------------------------------
This is an automatically generated e-mail. To reply, visit:
https://reviews.apache.org/r/633/#review561
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trunk/ql/src/java/org/apache/hadoop/hive/ql/parse/SemanticAnalyzer.java
<https://reviews.apache.org/r/633/#comment1196>

    I feel like it is a little hard to explain what this sample guarantees. It basically only
guarantees that we fetch at least the sampled percentage of source data. Not exact number,
nor guarantee for #rows. I think an option to disable it is a way to avoid confusion in some
ways. How do you think?



trunk/ql/src/java/org/apache/hadoop/hive/ql/parse/SemanticAnalyzer.java
<https://reviews.apache.org/r/633/#comment1197>

    limit can be combined with block sampling. Just this optimization for limit doesn't make
sense when users already sample the input data and we won't get much benefit.


- Siying


On 2011-04-20 18:28:29, 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 2011-04-20 18:28:29)
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 1095244 
bq.    trunk/conf/hive-default.xml 1095244 
bq.    trunk/ql/src/java/org/apache/hadoop/hive/ql/io/CombineHiveInputFormat.java 1095244

bq.    trunk/ql/src/java/org/apache/hadoop/hive/ql/io/HiveFileFormatUtils.java 1095244 
bq.    trunk/ql/src/java/org/apache/hadoop/hive/ql/optimizer/GenMRFileSink1.java 1095244 
bq.    trunk/ql/src/java/org/apache/hadoop/hive/ql/optimizer/GenMRTableScan1.java 1095244

bq.    trunk/ql/src/java/org/apache/hadoop/hive/ql/optimizer/GenMRUnion1.java 1095244 
bq.    trunk/ql/src/java/org/apache/hadoop/hive/ql/optimizer/GenMapRedUtils.java 1095244 
bq.    trunk/ql/src/java/org/apache/hadoop/hive/ql/optimizer/MapJoinFactory.java 1095244 
bq.    trunk/ql/src/java/org/apache/hadoop/hive/ql/parse/Hive.g 1095244 
bq.    trunk/ql/src/java/org/apache/hadoop/hive/ql/parse/ParseContext.java 1095244 
bq.    trunk/ql/src/java/org/apache/hadoop/hive/ql/parse/SemanticAnalyzer.java 1095244 
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 1095244 
bq.    trunk/ql/src/test/queries/clientnegative/split_sample_disabled.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_wrong_format.q.out PRE-CREATION

bq.    trunk/ql/src/test/results/clientpositive/bucket1.q.out 1095244 
bq.    trunk/ql/src/test/results/clientpositive/bucket2.q.out 1095244 
bq.    trunk/ql/src/test/results/clientpositive/bucket3.q.out 1095244 
bq.    trunk/ql/src/test/results/clientpositive/bucketmapjoin1.q.out 1095244 
bq.    trunk/ql/src/test/results/clientpositive/sample1.q.out 1095244 
bq.    trunk/ql/src/test/results/clientpositive/sample10.q.out 1095244 
bq.    trunk/ql/src/test/results/clientpositive/sample2.q.out 1095244 
bq.    trunk/ql/src/test/results/clientpositive/sample3.q.out 1095244 
bq.    trunk/ql/src/test/results/clientpositive/sample4.q.out 1095244 
bq.    trunk/ql/src/test/results/clientpositive/sample5.q.out 1095244 
bq.    trunk/ql/src/test/results/clientpositive/sample6.q.out 1095244 
bq.    trunk/ql/src/test/results/clientpositive/sample7.q.out 1095244 
bq.    trunk/ql/src/test/results/clientpositive/sample8.q.out 1095244 
bq.    trunk/ql/src/test/results/clientpositive/sample9.q.out 1095244 
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
>
>
> 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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