setting all variable values for DataSource at one time

Hi Gurus,

I am facing some issues in pulling data from source system into design studio and would appreciate your thought on this topic.  I have created 4 Data Sources in Design Studio that pull data from the same query.  DS_1 loads on startup with minimal set of data so that dashboard comes up quickly for users.  Next I have setup background processing for other three DataSources.  Here are my two questions that I am confused about:

1. DS_1, DS_2, DS_3, DS_4 all are set to pull data from same query (HANA Model to be precise).  So after DS_1 loads, and I am processing DS_2, will the data still be available for DS_1 or will it be over written?  In other words, does a DataSource holds its own data in design studio or it just reads it from query that it is built on?
2. I am using APPLICATION.setVariable("TimeStamp", time) to set variable values and then system is going and fetching the data.  So here is how I have set it up:

                DS_2.LoadSource();

                    if(Time =12)

                   APPLICATION.setVariableExt("TimeStamp", time1)  

                DS_3.LoadSource();

                    if(Time =3)

                    APPLICATION.setVariableExt("TimeStamp", time2)

               DS_4.LoadSource()

               if(Time =6)

               APPLICATION.setVariableExt("TimeStamp", time3)

I have to populate all the DS for my dashboard and I trying to think what would be a best possible method to go and get all 4 dataset without making four different calls.  I understand that I can bring the entire dataset and use setFilter but again when I reset, will the system  hold the values or go to database agian.

One more quick clarificaiton that I want...when we type DS_2.LoadSource();  does that mean we are only initializing that dataSource or does it mean that we are asking the system to run the query and get the data?