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From "Jean-Daniel Cryans (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HBASE-7700) TestColumnSeeking is mathematically bound to fail
Date Mon, 28 Jan 2013 23:11:12 GMT
Jean-Daniel Cryans created HBASE-7700:
-----------------------------------------

             Summary: 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: 0.94.4, 0.96.0
            Reporter: Jean-Daniel Cryans
            Assignee: Jean-Daniel Cryans
             Fix For: 0.96.0, 0.94.5


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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