Hi Lu Cao, In my previous experience on “cube” engine, no matter it is ROLAP or MOLAP, it is something above SQL layer, because it not only need user to establish cube schema by transform metadata from datawarehouse star schema but also the engine defines its own query language like MDX, and many times these languages are not standardized so that different vendor need to provide different BI tools or adaptors for it. So, although some vendor provides easy-to-use cube management tool, but it at least has two problems: vendor locking and the rigid of the cube mode once it defines. I think these problems are similar as in other vendor specific solution.
Currently one of the strength that carbon store provides is that it complies to standard SQL support by integrating with SparkSQL, Hive, etc. The intention of providing pre-aggregate table support is, it can enable carbon improve OLAP query performance but still stick with standard SQL support, it means all users still can use the same BI/JDBC application/tool which can connect to SparkSQL, Hive, etc. If carbon should support “cube”, not only need to defines its configuration which may be very complex and non-standard, but also will force user to use vendor specific tools for management and visualization. So, I think before going to this complexity, it is better to provide pre-agg table as the first step. Although we do not want the full complexity of “cube” on arbitrary data schema, but one special case is for timeseries data. Because time dimension hierarchy (year/month/day/hour/minute/second) is naturally understandable and it is consistent in all scenarios, so we can provide native support for pre-aggregate table on time dimension. Actually it is a cube on time and we can do automatic rollup for all levels in time. Finally, please note that, by using CTAS syntax, we are not restricting carbon to support pre-aggreagate table only, but also arbitrary materialized view, if we want in the future. Hope this make things more clear. Regards, Jacky like mandarin provides, Actually, as you can see in the document, I am avoiding to call this “cube”. > 在 2017年10月15日，下午9:18，Lu Cao <whuca...@gmail.com> 写道： > > Hi Jacky, > If user want to create a cube on main table, does he/she have to create > multiple pre-aggregate tables? It will be a heavy workload to write so many > CTAS commands. If user only need create a few pre-agg tables, current > carbon already can support this requirement, user can create table first > and then use insert into select statement. The only different is user need > to query the pre-agg table instead of main table. > > So maybe we can enable user to create a cube model( in schema or metafile?) > which contains multiple pre-aggregation definition and carbon can create > those pre-agg tables automatically according to the model. That would be > more easy for using and maintenance. > > Regards, > Lionel > > On Sun, Oct 15, 2017 at 3:56 PM, Jacky Li <jacky.li...@qq.com> wrote: > >> Hi Liang, >> >> For alter table, data update/delete, and delete segment, they are the same. >> So I write in document “ User can manually perform this operation and >> rebuild pre-aggregate table as >> update scenario” >> User need to drop the associated aggregate table and perform alter table, >> or data update/delete, or delete segment operation, then he can create the >> pre-agg table using CTAS command again, and the pre-aggregate table will be >> rebuilt. >> >> Regards, >> Jacky >> >>> 在 2017年10月15日，下午2:50，Liang Chen <chenliang6...@gmail.com> 写道： >>> >>> Hi Jacky >>> >>> Thanks for you started this discussion, this is a great feature in >>> carbondata. >>> >>> One question: >>> For sub_jar "Handle alter table scenarios for aggregation table", please >>> give more detail info. >>> Just i viewed the pdf attachment as below, looks no need to do any >> handles >>> for agg table if users do alter for main table. so can you provide more >>> detail, which scenarios need to be handled? >>> ------------------------------------------------------------ >> ------------------------------ >>> Adding of new column will not impact agg table. >>> Deleting or renaming existing column may invalidate agg tables, if it >>> invalidate, the operation >>> will be rejected. >>> User can manually perform this operation and rebuild pre-aggregate table >> as >>> update >>> scenario. >>> >>> Regards >>> Liang >>> >>> >>> -- >>> Sent from: http://apache-carbondata-dev-mailing-list-archive.1130556. >> n5.nabble.com/ >> >> >> >>
