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https://issues.apache.org/jira/browse/PIG-5311?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16305556#comment-16305556
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Koji Noguchi commented on PIG-5311:
-----------------------------------
Thanks Rohini.
For readability, I'm not sure if having
-- both rowProcessed and rowProcessedLong
is better than
-- having a single count and typecasting at multiple places.
I think latter is better but no strong preference.
Outside of that, found one critical issue.
Learning the "Reservoir sampling" from
https://en.wikipedia.org/wiki/Reservoir_sampling
and looking at the following change,
{code:java}
- int rand = randGen.nextInt(rowProcessed + 1);
+ int rand = randGen.nextInt(getPositiveVal(rowProcessed));
if (rand < numSamples) {
samples[rand] = res;
}
{code}
this breaks the reservoir sampling algorithm (when count is larger than
Integer.MAX_VALUE).
Random number generated here has to be from 0...rowProcessedLong in order to
preserve the feature of this algorithm: each item is kept with probability of
{{numSamples / total}}.
> POReservoirSample fails for more than Integer.MAX_VALUE records
> ---------------------------------------------------------------
>
> Key: PIG-5311
> URL: https://issues.apache.org/jira/browse/PIG-5311
> Project: Pig
> Issue Type: Bug
> Reporter: Rohini Palaniswamy
> Assignee: Rohini Palaniswamy
> Fix For: 0.18.0
>
> Attachments: PIG-5311-1.patch, PIG-5311-2.patch
>
>
> https://github.com/apache/pig/blob/branch-0.17/src/org/apache/pig/backend/hadoop/executionengine/physicalLayer/relationalOperators/POReservoirSample.java#L128
> The rowProcessed is a int. When it exceeds the int range it wraps around and
> becomes a negative number throwing below exception. It needs to be changed to
> long.
> {code}
> Caused by: java.lang.IllegalArgumentException: bound must be positive
> at java.util.Random.nextInt(Random.java:388)
> at
> org.apache.pig.backend.hadoop.executionengine.physicalLayer.relationalOperators.POReservoirSample.getNextTuple(POReservoirSample.java:128)
> at
> org.apache.pig.backend.hadoop.executionengine.physicalLayer.PhysicalOperator.processInput(PhysicalOperator.java:305)
> at
> org.apache.pig.backend.hadoop.executionengine.physicalLayer.relationalOperators.POForEach.getNextTuple(POForEach.java:284)
> {code}
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