Common Options
==============
 - optimize_empty_cache [boolean]
    If enabled, will prevent creation of aggregating CACHE records
    without any actual data records (i.e. over time interval when
    the data was not recorded) thus reducing the CACHE table size.
 
 - fill_raw_first [boolean]
    Instructs CACHE engine to file 'cache0' (raw data) tables before
    processing aggregating tables. This could drasticaly improve 
    performance in the cases when the data source is very slow in performing 
    selective data requests (for example, missing or invalid indexes in
    relational databases)
    
 - maximal_allowed_gap [integer] {seconds}
    Informs ADEI subsystems about maximal expected distance between sequential
    data records. If there are bigger intervals without any data recorded, 
    they should be reported as problematic.
    
 - min_resolution [integer] {seconds}
    Will prevent creation of CACHE tables with resolutions bellow
    specified
 
 - date_limit [date<ISO>], [date<ISO>, date<ISO>]
    Limits the time series to the specified date/time interval only. If single
    date value is specified, it defines beginning of the interval. Otherwise,
    array with two values defining the beginning and the end should be 
    specified.
    
 - resample [double] {seconds}
    Allows to resample source data before caching it in cache0 (raw) tables.
    This is intended to handle data sources with really intensive data rates
    if actually such inensity is not required.
    This option should be used with caution. Normally filling of raw cache is
    done in small iterations (min_resolution) and there could be extra points
    on edges. Even if 'fill_raw_first' is switched on, an extra points will 
    arise due to the caching application restarts.

    This means what normally minimal cache level should be significantly 
    bigger than resampling rate.

 - ignore_invalid_data [boolean]
    Just silently ignore (skip) invalid data records instead of throwing 
    exception to notify operator.

 - overcome_reader_faults [boolean]
    In this mode the CACHE will try to fullfil request even if connection to 
    the data source is failed.
 
 - use_cache_reader [boolean]
    In this mode teh CACHE will avoid access to the data source as much as
    possible.
    
 - use_md5_postfix [boolean]
    This instructs ADEI to create md5 checksums for naming of caching table
    instead of human readable names. Should be used if server/database/group
    names are using special symbols or too long.
    
 - ignore_subseconds [boolean]
    Allows CACHE to round all timing information to seconds

 - omit_raw_cache [boolean]
    This is not implemented at the moment, but intended to prevent caching 
    raw data. 

 - null_value [double]
    Numeric value which should be used instead of missing (NULL) values in
    numeric context.

 - cache_config
 - root_database
 - backup 
 - graph_interpolate [boolean]
 - optimize_time_axes [boolean]
 
 
DBReadeer Options
=================
    
TESTReader Options
==================
 - period [integer] {seconds}
    Sampling rate
    
 - items [custom]
    Array of items descriptions, each item is associative array containing
    * name: item name
    * func: function defining dependency of '$y' from '$x' (example: $y = $x)
    * noise: random noise (in percents [0-1])
