How can I decode a subset of fields from the summary data without reading every field?

kanchan
kanchan Newcomer
in UPA

I'm using UPA library to read and receive RWF
messages, and with each MarketByPrice message I'm only interested in a
subset of the summary data. Currently I'm having to decode every single
field to find the data that I'm interested in, which is costly. Is
there a way of only decoding the fields I'm interested in (e.g
QUOTE_DATE and QUOTIM_MS). I've found the documentation around
LocalFieldSetDefDb, but not quite sure this is the direction I'm
supposed to follow. If it is, please could you give an example of how I
could use LocalFieldSetDefDb to only read the summary data fields I'm
interested in.

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Best Answer

  • Jirapongse
    Jirapongse ✭✭✭✭✭
    Answer ✓

    You need to decode every field to find the fields that you are interested. However, you can skip decoding of the entry's contents by invoking the entry decoder to move to the next RsslFieldEntry. For example:

    while ((retVal = rsslDecodeFieldEntry(&decIter, &fieldEntry)) !=
    RSSL_RET_END_OF_CONTAINER)
    {
    	switch (fieldEntry->fieldId)
    	{
    	  case 3386: //QUOTE_DATE
    		//Decode QUOTE_DATE
    	  break;
    	  case 3855: //QUOTIM_MS
    		//Decode QUOTIM_MS
    	  break;
    	}
    	//For other fields, skip decoding its content  
    }

    Set Definition is used to reduce overall encoded content by eliminating repetitive type and length information. It is not used to find the content. Moreover, it is used within the RsslMap's entries, not summary data.

    For example, without set definition, the map entries in map will look like:

    image

    Each map entry will contain the FID 22 and 25.

    However, with set definition, the map entries in map will look like:

    image

    FID 22 and 25 are moved to set definition and the field list contains only the field's data. It provide additional optimizations for the size of payload.

    However, the application still needs to call decode for every field to get the data.

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