[
https://issues.apache.org/jira/browse/CRUNCH-601?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15423764#comment-15423764
]
Micah Whitacre commented on CRUNCH-601:
---------------------------------------
So I think I figured out the reason but not really sure of the fix just yet.
When doing a .length()[1] call it then calls Aggregate.length(this) and does
this[2].
The issue is that the "count" PCollection in that method it has 4 different
parents. It does calculate the expected size of the PCollection to proactively
materialize or not by using the scaleFactor * parent. So for a collection of
size 1 it is essentially calculating (.99f * (long)(.99f * (long)(.99f *
(long)(.99f *1)))). And casting to long causes it to round down. so the first
.99f * 1 = 0 when cast to a long. So the smaller values are invalid because
the scale factor makes their size go to zero which then makes the materialize
call return the empty PCollection.
[1] -
https://github.com/apache/crunch/blob/0b19717d105b58e58c1947eda6b673a387e330d0/crunch-core/src/main/java/org/apache/crunch/impl/dist/collect/PCollectionImpl.java#L284
[2] -
https://github.com/apache/crunch/blob/0b19717d105b58e58c1947eda6b673a387e330d0/crunch-core/src/main/java/org/apache/crunch/lib/Aggregate.java#L94
> Short PCollections in SparkPipeline get length null.
> ----------------------------------------------------
>
> Key: CRUNCH-601
> URL: https://issues.apache.org/jira/browse/CRUNCH-601
> Project: Crunch
> Issue Type: Bug
> Components: Spark
> Affects Versions: 0.13.0
> Environment: Running in local mode on Mac as well as in a ubuntu
> 14.04 docker container
> Reporter: Mikael Goldmann
> Priority: Minor
> Attachments: SmallCollectionLengthTest.java
>
>
> I'll attach a file with a test that I would expect to pass but which fails.
> It creates five PCollection<String> of lengths 0, 1, 2, 3, 4 gets the
> lengths, runs the pipeline and prints the lengths. Finally it asserts that
> all lengths are non-null.
> I would expect it to print lengths 0, 1, 2, 3, 4 and pass.
> What it does is print lengths null, null, null, 3, 4 and fail.
> I think the underlying reason is the use of getSize() on an unmaterialized
> object and assuming that when the estimate that getSize() returns is 0, then
> the PCollection is guaranteed to be empty, which is false in some cases.
--
This message was sent by Atlassian JIRA
(v6.3.4#6332)
