SAMPLE shouldn't be pushed up
-----------------------------
Key: PIG-2014
URL: https://issues.apache.org/jira/browse/PIG-2014
Project: Pig
Issue Type: Bug
Reporter: Jacob Perkins
Consider the following code:
{code:none}
tfidf_all = LOAD '$TFIDF' AS (doc_id:chararray, token:chararray, weight:double);
grouped = GROUP tfidf_all BY doc_id;
vectors = FOREACH grouped GENERATE group AS doc_id, tfidf_all.(token, weight)
AS vector;
DUMP vectors;
{code}
This, of course, runs just fine. In a real example, tfidf_all contains
1,428,280 records. The reduce output records should be exactly the number of
documents, which turn out to be 18,863 in this case. All well and good.
The strangeness comes when you add a SAMPLE command:
{code:none}
sampled = SAMPLE vectors 0.0012;
DUMP sampled;
{code}
Running this results in 1,513 reduce output records. The reduce output records
be much much closer to 22 or 23 records (eg. 0.0012*18863).
Evidently, Pig rewrites SAMPLE into filter, and then pushes that filter in
front of the group. It shouldn't push that filter
since the UDF is non-deterministic.
Quick fix: If you add "-t PushUpFilter" to your command line when invoking pig
this won't happen.
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