[jira] [Commented] (HBASE-7700) TestColumnSeeking is mathematically bound to fail

["Lars Hofhansl (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HBASE-7700?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13586749#comment-13586749 ] 

Lars Hofhansl commented on HBASE-7700:
--------------------------------------

+1 on patch. Randomness is fine as long as it is repeatable (as Elliot says) and we do not rely on any specific distribution.
This is a good short-term fix; I'll will commit this tomorrow, unless I hear a strong case against it.

We can also file a followup issue to change/remove the randomness in favor of a different mechanism.

                
> TestColumnSeeking is mathematically bound to fail
> -------------------------------------------------
>
>                 Key: HBASE-7700
>                 URL: https://issues.apache.org/jira/browse/HBASE-7700
>             Project: HBase
>          Issue Type: Bug
>    Affects Versions: 0.96.0, 0.94.4
>            Reporter: Jean-Daniel Cryans
>            Assignee: Jean-Daniel Cryans
>             Fix For: 0.96.0, 0.94.6
>
>         Attachments: HBASE-7700-0.94-lazyfix.patch
>
>
> First I'd like to say that TestColumnSeeking is a bad test. It's not documented, it's non-deterministic, it's 2 methods with almost the same code.
> So in each test it populates column lists this way:
> {code}
>     for (int i = 0; i < numberOfTests; i++) {
>       kvMaps[i] = new HashMap<String, KeyValue>();
>       columnLists[i] = new ArrayList<String>();
>       for (String column : allColumns) {
>         if (Math.random() < selectPercent) {
>           columnLists[i].add(column);
>         }
>       }
>     }
> {code}
> Since selectPercent is 50% and there are 10 columns, there's something like a 1/1024 chance that one of the column list ends up with 0 column. This is later mismanaged in the checks. First something like this will be printed out:
> bq. 2013-01-28 11:50:02,200 INFO  [pool-1-thread-1] regionserver.TestColumnSeeking(140): Columns: 0  Keys: 0
> Like it says, there's 0 columns so it couldn't add data. But then it still makes sure later that the data is there with this check:
> {code}
> assertEquals(kvSet.size(), results.size());
> {code}
> Do notice that the parameters are reversed, and here the results.size() will be 0 since there are 0 columns for this test.
> I see multiple ways to fix this:
>  - Skip tests that have 0 columns
>  - Change the randomness to at least have 1 column (like select 1 + 0..9 columns)
>  - Redo the whole unit test to not rely on randomness

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