The cost of joint dimension compared with extended column is you have more
columns in the HBase rowkey. It may harm the query performance. But most
time, joint dimension is still recommended, since the normal dimension
column supports much more functions than extended column, such as count(*).
2016-12-01 17:07 GMT+08:00 Alberto Ramón <a.ramonporto...@gmail.com>:
> I was preparing a email with related doubts:
> Some times we have derived dimensions with relation 1:1, examples:
> WeekDayID & WeekDayTxt
> MonthID & WeekTxt
> SOL1: Derived. ID as Host and Txt Extended
> PB: You can't filter / Group by Txt
> SOL2: Joint. Define tuples of ID & TXT
> Some PB/limitation? (I need test this option)
> 2016-12-01 0:35 GMT+01:00 Billy(Yiming) Liu <liuyiming....@gmail.com>:
>> Thanks, Alberto. The explanation is accurate. EXTENDED_COLUMN is only
>> used for representation, but not filtering or grouping which is done by
>> HOST_COLUMN. So EXTENDED_COLUMN is not a dimension, it works like a
>> key/value map against the HOST_COLUMN.
>> If the value in EXTENDED_COLUMN is not long, you could just define two
>> dimensions with joint dimension setting, it has almost the same performance
>> impact with EXTENDED_COLUMN which reduces one dimension, but better
>> 2016-11-30 19:00 GMT+08:00 Alberto Ramón <a.ramonporto...@gmail.com>:
>>> This will help you
>>> The idea is always, How I can reduce the number of Dimension ?
>>> If you reduce Dim, the time / resources to build the cube and final size
>>> it decrease --> Its good
>>> An example can be DIM_Persons: Id_Person , Name, Surname, Address, .....
>>> Id_Person can be HostColumn
>>> and other columns can be calculated from ID --> are Extended Column
>>> 2016-11-30 11:35 GMT+01:00 仇同心 <qiutong...@jd.com>:
>>> > Hi ,all
>>> > I don’t understand the usage scenarios of EXTENDED_COLUMN,although I
>>> > this article “https://issues.apache.org/jira/browse/KYLIN-1313”.
>>> > What,s the means about parameters of “Host Column” and “Extended
>>> > Why use this expression,and what aspects of optimization that this
>>> > expression solved?
>>> > Can be combined with a SQL statement to explain?
>>> > Thanks~
>> With Warm regards
>> Yiming Liu (刘一鸣)
With Warm regards
Yiming Liu (刘一鸣)