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https://issues.apache.org/jira/browse/KYLIN-1677?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15296155#comment-15296155
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Dayue Gao commented on KYLIN-1677:
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Hi Shaofeng,
Looked at your commits, couple of thoughts:
* the reason why I added RedistributeFlatHiveTableStep after FlatHiveTableStep
is because fact table could actually be a Hive view. In that case, if you first
do a count and then create flat table, the view definition is run twice, which
may be expensive.
* use row count of fact table may be inaccurate, consider left join.
> Distribute source data by certain columns when creating flat table
> ------------------------------------------------------------------
>
> Key: KYLIN-1677
> URL: https://issues.apache.org/jira/browse/KYLIN-1677
> Project: Kylin
> Issue Type: Improvement
> Components: Job Engine
> Reporter: Shaofeng SHI
> Assignee: Shaofeng SHI
> Fix For: v1.5.3
>
>
> Inspired by KYLIN-1656, Kylin can distribute the source data by certain
> columns when creating the flat hive table; Then the data assigned to a mapper
> will have more similarity, more aggregation can happen at mapper side, and
> then less shuffle and reduce is needed.
> Columns can be used for the distribution includes: ultra high cardinality
> column, mandantory column, partition date/time column, etc.
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