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https://issues.apache.org/jira/browse/KYLIN-2764?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16178077#comment-16178077
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liyang commented on KYLIN-2764:
-------------------------------
For a UHC column, if all values must gather to one reducer to build Global
dictionary (like the UHCDictionaryReducer.java below), then why not just assign
one reducer per column in the "Extract Fact Table Distinct Columns" job and
build the dictionary there? That's my confusion. I don't see the reason to add
a new UHCDictionaryJob.
https://github.com/apache/kylin/commit/ccd076861415a40926ab42e6f9b71cd5258d4daf
> Build the dict for UHC column with MR
> -------------------------------------
>
> Key: KYLIN-2764
> URL: https://issues.apache.org/jira/browse/KYLIN-2764
> Project: Kylin
> Issue Type: Improvement
> Components: Job Engine
> Affects Versions: v2.0.0
> Reporter: kangkaisen
> Assignee: kangkaisen
> Attachments: job-memory-after.png, job-memory-before.png
>
>
> KYLIN-2217 has built dict for normal column with MR, but the UHC column
> still build dict in JobServer. Like KYLIN-2217, we also could use MR build
> dict for UHC column. which could thoroughly release the memory pressure and
> improve job concurrent for JobServer as well as speed up multi UHC columns
> procedure.
> The MR input is the output of "Extract Fact Table Distinct Columns", the MR
> output is the UHC column dict. Because it is very hard build global dict with
> multi reducers, I use one reducer handle one UHC column and allocate enough
> memory to the reducer. According to my test, 8G memory is enough.
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