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https://issues.apache.org/jira/browse/HIVE-19671?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16518745#comment-16518745
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Xuefu Zhang commented on HIVE-19671:
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Based on your analysis, it seems that random(see) depends on a deterministic
order of the data. Reading HDFS may guarantee the order, but probably not every
data source has such guaranty. Also, a map or reduce logic may also generate
nondeterministic order. Having said that, it appears to me that any
partitioning that depends on a deterministic ordering of the data is doomed,
include rand() and rand(seed). This is rather a user problem, for which I'm not
sure if Hive needs to do anything. We may document this as a general bad
practice, but blocking solves rand() problemI but doesn't help other similar
problems. I suggest we leave it to user to solve the problem. Thoughts?
> Distribute by rand() can lead to data inconsistency
> ---------------------------------------------------
>
> Key: HIVE-19671
> URL: https://issues.apache.org/jira/browse/HIVE-19671
> Project: Hive
> Issue Type: Bug
> Reporter: Rui Li
> Assignee: Rui Li
> Priority: Major
>
> Noticed the following queries can give different results:
> {code}
> select count(*) from tbl;
> select count(*) from (select * from tbl distribute by rand()) a;
> {code}
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