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https://issues.apache.org/jira/browse/HIVE-2121?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13025465#comment-13025465
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jirapos...@reviews.apache.org commented on HIVE-2121:
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bq. On 2011-04-26 20:50:30, Siying Dong wrote:
bq. > trunk/ql/src/java/org/apache/hadoop/hive/ql/parse/SemanticAnalyzer.java,
line 498
bq. > <https://reviews.apache.org/r/633/diff/1/?file=16093#file16093line498>
bq. >
bq. > 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?
I think if we specify clearly the semantics of block-level sample in the
wiki/documentation, there shouldn't be much confusion. In fact I think it is
much easier to explain than the bucket-based sampling. In addition if the user
has confusions about the semantics, throwing an SemanticException won't help
them understand. I think the only use case for this parameter is to act as a
gatekeeper to this feature if we found a bug in it and want to disable the
feature quickly. That should be able to be achieved by switching branches
quickly. If we have a gatekeeper parameter for each feature, the conf will grow
unnecessarily large quickly.
bq. On 2011-04-26 20:50:30, Siying Dong wrote:
bq. > trunk/ql/src/java/org/apache/hadoop/hive/ql/parse/SemanticAnalyzer.java,
line 6392
bq. > <https://reviews.apache.org/r/633/diff/1/?file=16093#file16093line6392>
bq. >
bq. > 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.
I think combining these two still makes sense: 1) as you mentioned block
sampling is not limiting on the # of rows, but limit is. Combining these two
allows the users to get approximately N rows quickly. 2) this restriction makes
an exception in terms of the query language composition. From the language
syntax, it is allowed and makes senses to combine block-sampling and limit, but
the user will get a SemanticException if they do. I think SemanticException
should be thrown only when there is a legitimate semantic error (e.g., the
percentage number is negative). If you feel that it is not a major use case and
would rather do it in a follow-up JIRA, we should document it in TODO and file
a JIRA for it.
- Ning
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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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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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