[jira] [Created] (PIG-4960) Split followed by order by/skewed join is skewed

["Rohini Palaniswamy (JIRA)" <ji...@apache.org>]

Rohini Palaniswamy created PIG-4960:
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             Summary: Split followed by order by/skewed join is skewed
                 Key: PIG-4960
                 URL: https://issues.apache.org/jira/browse/PIG-4960
             Project: Pig
          Issue Type: Bug
            Reporter: Rohini Palaniswamy
            Assignee: Rohini Palaniswamy
             Fix For: 0.17.0, 0.16.1


Sampling is not done right. Split is a special case as EOP is returned after each record is processed. We did fixes for that before (PIG-4480, etc), but still it is not done right.  

   In case of skewed join, skipInterval is applied for each record instead of all the records. So except for the first record all the other records are mostly skipped. Sampling is slightly better if it is group by followed by skewed join on a different key as there is a bag of input to Split and there are multiple records.  

  In case of order by, samples were being returned even as they were being updated with new data. So samples mostly contained records from the first few hundreds of rows.  Sampling is slightly better in this case also if it is group by followed by order by on a different key.



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