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https://issues.apache.org/jira/browse/KYLIN-2286?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16139845#comment-16139845
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Billy Liu commented on KYLIN-2286:
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I think this is Slowly Changing Dimension(SCD) topic. For more info, check
http://datawarehouse4u.info/SCD-Slowly-Changing-Dimensions.html
The issue becomes more complicated when dealing with normal dimension and
derived dimension in lookup table.
To support Type 0 - The passive method, use normal dimension in lookup table.
To support Type 1 - Overwriting the old value, use derived dimension in lookup
table.
To support Type 0 with derived dimension will use global snapshot table like
this issue.
This feature is welcomed, to support more flexible Kylin.
> global snapshot table for one cube
> -----------------------------------
>
> Key: KYLIN-2286
> URL: https://issues.apache.org/jira/browse/KYLIN-2286
> Project: Kylin
> Issue Type: Improvement
> Reporter: fengYu
> Assignee: fengYu
>
> I current version, Kylin build a snapshot table for a segment and isolate
> with each other in the same cube, even though some segments share the same
> snapshot table storage .
> I some scene， we need global snapshot table for one cube, such as we has a
> cube with snapshot table,ID is PK，the first day, the table look like:
> id name
> 1 A
> 2 B
> 3 C
> the query 'select name, count(1) from fact join dimension group by name' get
> result:
> A xx
> B xx
> C xx
> the next day(segment), lookup table modified, it looks like :
> id name
> 1 A
> 2 D
> 3 E
> the same query return :
> A xx
> B xx
> C xx
> D xx
> E xx
> However B and D, C and E has the same ID, we need the newest result. so a
> global snapshot table shared by all segments which has always the newest
> values is needed.
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