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From "Ben Slater (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-12744) Randomness of stress distributions is not good
Date Sun, 28 May 2017 09:38:04 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-12744?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16027755#comment-16027755
] 

Ben Slater commented on CASSANDRA-12744:
----------------------------------------

Actually, I think it's a bit more complex than I just said but still think it's related to
the interaction between the population distribution and the individual column distributions.
Just tried 10,000 inserts with -pop dist=uniform(1..25) and the following YAML and only get
1 row inserted. 
table_definition: |
  CREATE TABLE test4 (
        pk text,
        pk2 text,
        val text,
        PRIMARY KEY ((pk,pk2))
  ) 
columnspec:
  - name: pk
    size: fixed(2) 
    population: exp(1..5) 
  - name: pk2
    size: fixed(2) 
    population: exp(1..5)

Running with -pop dist=uniform(1..10B) gives the expected 25 rows so it may be as simple as
just setting a really big default population when running in user mode but I'll do a bit more
digging.

> Randomness of stress distributions is not good
> ----------------------------------------------
>
>                 Key: CASSANDRA-12744
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-12744
>             Project: Cassandra
>          Issue Type: Bug
>          Components: Tools
>            Reporter: T Jake Luciani
>            Assignee: Ben Slater
>            Priority: Minor
>              Labels: stress
>             Fix For: 4.0
>
>
> The randomness of our distributions is pretty bad.  We are using the JDKRandomGenerator()
but in testing of uniform(1..3) we see for 100 iterations it's only outputting 3.  If you
bump it to 10k it hits all 3 values. 
> I made a change to just use the default commons math random generator and now see all
3 values for n=10



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