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From "Enis Soztutar (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HBASE-9759) IntegrationTestBulkLoad random number collision
Date Tue, 15 Oct 2013 00:52:41 GMT
Enis Soztutar created HBASE-9759:
------------------------------------

             Summary: IntegrationTestBulkLoad random number collision
                 Key: HBASE-9759
                 URL: https://issues.apache.org/jira/browse/HBASE-9759
             Project: HBase
          Issue Type: Bug
          Components: test
            Reporter: Enis Soztutar
            Assignee: Enis Soztutar
             Fix For: 0.98.0, 0.96.1


ITBL failed recently in our test harness. Inspecting the failure made me believe that the
only reason that particular failure might have happened is that there is a collision in random
longs generated by the test. 

The test creates 50 mappers by default, and each mapper writes a 500K random rows starting
with row = 0. By default there are 5 iterations.

The check job outputs these counters: 
{code}
2013-10-13 07:48:01,134 Map input records=124999751
2013-10-13 07:48:01,134 Map output records=124999999
{code}
The number of input records seems fine because
{code}
124999751 = 1 + 5 * (0.5M - 1) * 50
{code}
5 = num iterations, 0.5M = num rows, 50 = num mappers, and 1 is for row =0 which every chain
writes to. 

Output records should be 125M, however we see one cell missing. Since the map input records
matches expected number of distinct rows, I suspect that row = 0 had a collision. 

In one of the generate jobs, we can see that the reducer output count does not match the reducer
input count. Given that we are using KVSortReducer, this confirms that there is a collision
in KeyValues received by this task.
{code}
2013-10-13 06:48:12,738 Reduce input records=75000000
2013-10-13 06:48:12,738 Reduce output records=74999997
{code}
The count is off by 3 because we are writing 3 columns per row. 

My only theory for explaining this is that we had a collision in chainId's or one of the chains
reused row = 0 as the next row. 

This is similar to HBASE-8700, however, in this the probability is much much much lower. 



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