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From "Kim Jin Chul (Code Review)" <ger...@cloudera.org>
Subject [Impala-ASF-CR] IMPALA-5754: Improve randomness of rand()/random()
Date Wed, 08 Nov 2017 07:14:01 GMT
Kim Jin Chul has posted comments on this change. ( http://gerrit.cloudera.org:8080/8355 )

Change subject: IMPALA-5754: Improve randomness of rand()/random()
......................................................................


Patch Set 3:

(6 comments)

E2E test has not been ready.

http://gerrit.cloudera.org:8080/#/c/8355/3//COMMIT_MSG
Commit Message:

http://gerrit.cloudera.org:8080/#/c/8355/3//COMMIT_MSG@11
PS3, Line 11: in C++11 libarary
> "in the C++11 standard library"
Done


http://gerrit.cloudera.org:8080/#/c/8355/3//COMMIT_MSG@12
PS3, Line 12: because it has much longer period than that of rand in C.
> It does show better randomness, and it does have a longer period, but it do
Removed


http://gerrit.cloudera.org:8080/#/c/8355/3//COMMIT_MSG@13
PS3, Line 13: (More details in http://www.pcg-random.org/)
> That's a site promoting a different generator. If you want to list a citati
Removed


http://gerrit.cloudera.org:8080/#/c/8355/3//COMMIT_MSG@17
PS3, Line 17: t1
> This is not a reproducable test case without knowing what t1 is. You can us
Removed the example


http://gerrit.cloudera.org:8080/#/c/8355/3//COMMIT_MSG@23
PS3, Line 23: 
            : * After
            : > select count(distinct(rand(1))), count(*) from t1
            : +---------------------------+-----------+
            : | count(distinct (rand(1))) | count(*)  |
            : +---------------------------+-----------+
            : | 34603008                  | 103809024 |
            : +---------------------------+-----------+
            : 
            : You may expect maximum randomness(e.g. 103809024).
            : Due to the issue IMPALA-6117, randomness could be
            : "maximum randomess / n". "n" means the number of Impala
            : execution engines. n is 3 in this example and each
            : execution engine loads and processes data in parallel.
            : 
            : This change introduces a new utility code for random because
            : we have a plan to replace the legacy in IMPALA-4954 with
            : the utility code.
> I'd say this whole section is overkill.
Removed


http://gerrit.cloudera.org:8080/#/c/8355/3/be/src/exprs/expr-test.cc
File be/src/exprs/expr-test.cc:

http://gerrit.cloudera.org:8080/#/c/8355/3/be/src/exprs/expr-test.cc@4652
PS3, Line 4652:   {
> You can reduce this code size and make it more robust to future changes to 
Done



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Gerrit-Project: Impala-ASF
Gerrit-Branch: master
Gerrit-MessageType: comment
Gerrit-Change-Id: Idafdd5fe7502ff242c76a91a815c565146108684
Gerrit-Change-Number: 8355
Gerrit-PatchSet: 3
Gerrit-Owner: Kim Jin Chul <jinchul@gmail.com>
Gerrit-Reviewer: Jim Apple <jbapple-impala@apache.org>
Gerrit-Reviewer: Kim Jin Chul <jinchul@gmail.com>
Gerrit-Comment-Date: Wed, 08 Nov 2017 07:14:01 +0000
Gerrit-HasComments: Yes

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