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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