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From ShaoFeng Shi <shaofeng...@apache.org>
Subject Re: usage of Web inteface Kylin an performances
Date Sun, 18 Feb 2018 02:22:39 GMT
Hi Jean-luc,

Most of the Kylin developers are in the new year holiday, so there might be
some delay. Here are some comments from my side:

1.  I presume that the whole .json files are stored, is it right ?
yes
2. Do these kinds of tables contain the cube data ?
yes; cube are stored in HBase with "KYLINL_" as prefix
3. So I am wondering if it is the good method
the "compression" in Tomcat/conf/server.xml has nothing with cube build. To
enable compression for cube, you need to configure that in your Hadoop
configurations like mapred-site.xml, hbase-site.xml or
kylin/conf/kylin_job_conf.xml.
4. How is it possible to optimize cube size to keep good performance ?
https://kylin.apache.org/docs21/howto/howto_optimize_cubes.html
5.  Is it through the ‘rowkeys’ in the advanced settings when you build the
cube ?
yes, exactly; putting the most used filtering column to the heading
position on the rowkey can get better performance.
6. What shall we put exactly in the ‘Rowkeys’ section ?
All dimensions (excluding 'derived' dimensions) need be on rowkey; If you
see too many columns in the agg. group, remove some dimensions from your
cube.
7.  Are the aggregation groups used for speed of the queries.
The agg. group is used to optimize the dimension combinations. For a N
dimension cube, by default it will have 2^N combinations (we called
cuboid). If you can divide N dimensions to several groups, the combination
numbers can be greatly reduced, so the cube build will be much easier and
taking much less space. How to define the agg. group? You can do that with
your business query patterns.



2018-02-14 1:49 GMT+08:00 BELLIER Jean-luc <jean-luc.bellier@rte-france.com>
:

> Hello,
>
>
>
> I have several questions on Kylin, especially about performances and how
> to manage them. I would like to understand precisely how it works to see if
> I can use it in my business context.
>
>
>
> I come from the relational database world, so as far as I understand on
> OLAP, the searches are performed on the values of primary keys in
> dimensions. These subsets are then joined to get the corresponding lines on
> the facts table. As the dimensions tables are much smaller than the facts
> table, the queries run faster
>
>
>
> *1.       **Questions on performances*
>
> ·         the raw data are stored in Hive, and the models and structures
> (cubes) are stored in HBase; I presume that the whole .json files are
> stored, is it right ?
>
> ·         Where are the cube results stores (I mean after a build, a
> refresh or an append action). Is it also in HBase ? I can see in HBase
> tables like "KYLIN_FF46WDAAGH". Do these kinds of tables contain the cube
> data ?
>
> ·         I noticed that when I build the ‘sample_cube’, the volume of
> data was very important compared to the size of the original files. Is
> there a way to reduce it (I saw a attribute in the $KYLIN_HOME/tomcat/conf/server.xml
> file, called ‘compression’ for the connector on port 7070, but I do not
> know if it is related to the cube size). I tried to change this parameter
> to ‘yes’, but I noticed a huge increase of the duration of cube generation.
> So I am wondering if it is the good method.
>
> ·         How is it possible to optimize cube size to keep good
> performance ?
>
> ·         In Hive, putting indexes is not recommended. So how Kylin is
> ensuring good performance when querying high volumes of data  ? Is it
> through the ‘rowkeys’ in the advanced settings when you build the cube ?
>
> Or is the answer elsewhere ?
>
>
>
> *2.       **Questions on cube building*
>
> ·         By the way, the ‘Advanced settings’ step is still unclear for
> me. I tried to build a cube from scratch using the tables provided in the
> sample project. But I do not know very much what to put in this section.
>
> ·         My goal is to define groups of data on YEAR_BEG_DT,
> QTR_BEG_DT,MONTH_BEG_DT.
>
> ·         I do not understand very well why the aggregation group
> contains so many columns. I tried to remove as many as possible, but when I
> tried to set up the joins, but some fields were missing so the saving of
> the cube failed.
>
> ·         What shall we put exactly in the ‘Rowkeys’ section ? I
> understand that this is used to define data encoding (for speed access ?
> ).Am I right ?
>
> ·         Are the aggregation groups used for speed of the queries. I
> assume it is the case, because it represents the most commonly used
> associations of columns for the cube.
>
>
>
> Thank you in advance for your help.
>
>
>
> Best regards,
>
> Jean-Luc.
>
>
>
>
>
>
>
>
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-- 
Best regards,

Shaofeng Shi 史少锋

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