DBReader
========
 - GetGroupInfo                                         - apply intervals
        SHOW TABLES
        SELECT MIN(*), MAX(*) ...
 - GetItemList                                          - headers
        SHOW COLUMNS
 - GetRawData                                           - load data
        SHOW COLUMNS                                    - construct SELECT query 
        SELECT                                          - request data

Optimization
============
 - General
    * Better use direct addressing instead of virtual
    * Group requests to the same group (requests all required channels at once)
    * Cache fetched data locally

 - Avoiding interval calculation
    experiment=*-*                                      - We don't need to find where the data ends and will not call
                                                        GetGroupInfo if 'window=#' 
    window=3600,-1                                      - The last would not work unless window has a defined size. 
                                                        Therefore, we not only request last item, but also specify window to look.
    
 - Avoiding names retrieval
    rt=skip_headers                                     - Will not call GetItemList
    rt=full                                             - Also adapts window & experiment as explained above
    
 - Loading data from the cache
    cache=1                                             - SHOW COLUMNS will not be called for DBReader & data is loaded from MySQL cache
    
 - Completely excluding source DB                       
    rt=full&cache=1