Fragmentation in OBIEE

Question

Version = OBIEE 10.1.3.3
I need some help getting fragmentation to work correctly.
I have two tables SALES and SALES_HIST.
SALES has all date after 2/1/1998
SALES_HIST has all data before 2/1/1998
I have created a logical table "SALES" in the BMM and set the sources to SALES and SALES_HIST. In the fragmentation field on the content tab, this is what I have entered -
For SALES = "Sales History (SH)".Times."Time ID" >= '01/01/1998' AND "Sales History (SH)".Times."Time ID" <= '01/31/1998'
For SALES_HIST = "Sales History (SH)".Times."Time ID" > '01/31/1998' AND "Sales History (SH)".Times."Time ID" < '12/31/2008'
When I query for data in Answers without any filter, Answers returns all data from SALES and SALES_HIST. That is great because thats what I expect OBIEE to do. When I look in the NQuery.log, I see a UNION ALL between SALES and SALES_HIST which is what I expected.
However, when I add a filter a filter for example -
TIME_ID >= '01/20/1998' AND TIME_ID <= '2/25/1998'
and run the query it returns data only upto 1/31/2008. When I look at NQuery.log, I only see a query against SALES_HIST table.
The SALES table is not being queried at all. I would appreciate it if someone can give me some pointers about what could be wrong.
Thanks

Answer 1

Suppose you have 1 million rows fact table, but 20% are requested 80% of time, by 80% of users.
For example : these 20% represents the current and previous year facts (interesting data for analyst), and the 80% left are old data.
You don't want to "read" these 1 million rows each time a report wants to display the 20%.
So, in your ETL, you split the data into 2 tables (or more). The first one (we'll call it Fact_main) has the 20% data, and the second one (Fact_old) the 80% old data.
Now, in OBIEE :
- in the physical layer : you insert all the tables. Each of the 2 fact table are linked to the correct dimensions.
- n the logical layer : only 1 logical fact table with 2 sources.
BUT, OBIEE has to choose the right source depending on the request. And, sometimes, OBIEE has to do use the 2 sources at the same time (if you want to request data for the 3 or more last years, for example).
So, in the logical source definition, in "content" page, you'll define the "fragmentation" option by putting : "dim_time.year in (2010, 2009)" (or use variable like current year) in one, and dim_time.year <= (2008) in the second one. Then, active the option : "this source will be combined...".
In Answers :
- if you do a report with a filter "year > 2009", only the first source will be used
- if you do a report with a filter "year <= 2008", only the second source will be used
- if you do a report without any filter on the year, the 2 sources will be used (thanks to a Union)
Another case : an international company has a big fact table and a big customer table, with fact and clients from all the world. But you know that in 80% of case, end-users analysts will be focus on 1 country based on their organization. So you will fragmente data : 1 table for France, 1 table for USA, 1 table for Spain etc. Or, 1 table for Europe, 1 for North America, and so on... But only 1 logical table in your logical layer.