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https://issues.apache.org/jira/browse/SPARK-14393?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15560991#comment-15560991
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Hyukjin Kwon commented on SPARK-14393:
--------------------------------------
Thanks for pinging me!, in my personal opinion, we should document this first
if we can have some concrete reasons that why it is virtually the limitation in
the current implementation.
I haven't look into this but I *guess* it can be documented as I *guess* it
seems pretty easy to reproduce but it seems not fixed for several months.
I *think* (and as you already know) it is fine to submit a PR if we have a good
reason to support the PR whether it is about documentation or the actual fix :)
> monotonicallyIncreasingId not monotonically increasing with downstream
> coalesce
> -------------------------------------------------------------------------------
>
> Key: SPARK-14393
> URL: https://issues.apache.org/jira/browse/SPARK-14393
> Project: Spark
> Issue Type: Bug
> Components: SQL
> Affects Versions: 1.6.0
> Reporter: Jason Piper
>
> When utilising monotonicallyIncreasingId with a coalesce, it appears that
> every partition uses the same offset (0) leading to non-monotonically
> increasing IDs.
> See examples below
> {code}
> >>> sqlContext.range(10).select(monotonicallyIncreasingId()).show()
> +---------------------------+
> |monotonicallyincreasingid()|
> +---------------------------+
> | 25769803776|
> | 51539607552|
> | 77309411328|
> | 103079215104|
> | 128849018880|
> | 163208757248|
> | 188978561024|
> | 214748364800|
> | 240518168576|
> | 266287972352|
> +---------------------------+
> >>> sqlContext.range(10).select(monotonicallyIncreasingId()).coalesce(1).show()
> +---------------------------+
> |monotonicallyincreasingid()|
> +---------------------------+
> | 0|
> | 0|
> | 0|
> | 0|
> | 0|
> | 0|
> | 0|
> | 0|
> | 0|
> | 0|
> +---------------------------+
> >>> sqlContext.range(10).repartition(5).select(monotonicallyIncreasingId()).coalesce(1).show()
> +---------------------------+
> |monotonicallyincreasingid()|
> +---------------------------+
> | 0|
> | 1|
> | 0|
> | 0|
> | 1|
> | 2|
> | 3|
> | 0|
> | 1|
> | 2|
> +---------------------------+
> {code}
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