topic structure

[Toby Dickenson]

Hi,

I'm looking for some advice or examples on best practice for topic structure. In particular, I dont have any intuition about how much information to pack into one message.

For example, if we were considering some messages:
/sensor/<id>/temperature/value 21.2
/sensor/<id>/temperature/timestamp 2014-03-25 19:28:51

Would it be better to combine that all into one message:
/sensor/<id>/temperature 2014-03-25 19:28:51, 21.2

That has the advantage of atomicity (no chance of a client seeing a new value with the old timestamp), at the expense of needing a little parser for a format that might not be quite so universal.

Thanks in advance,

[Nicholas O'Leary]

Hi Toby,

you are much better off publishing a single message with all of the data for that event in it. Trying to split a single 'event' into multiple messages published to multiple topics will give you a headache when it comes to correlating the messages back into a single event.

Nick

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[Dominik Obermaier]

Hi Toby,

I think there is no golden rule how to do this, I personally am in strong favor of the "one message with all data". You probably have to write your own parser for the payload anyway.

If you are worried about writing your own parsers or if you are worried about the added overhead of too much data in the payload, you could use Protobuf or Msgpack for the payload.


Toby Dickenson wrote:

[Darren Clark]

I use JSON myself. Although I don't have to worry about bandwidth so much. Still reasonably compact. Every message has two properties, time, which is a local timestamp, and value, that is a JSON object.

-D

[Nicholas O'Leary]

Sometimes simple csv is all you need.

[Tomoaki Yamaguchi]

I use the binary data structure as follows:   When, Where and Value

struct measurementData{

    uint32_t      utc

    int32_t        latitude     

    int32_t        longitude

    int16_t        altitude

    uint8_t        valueType     //  1:fValue, 2: lValue, 3: iValue

    union          value{

             float      fValue

             long      lValue

             int          iValue

       }

}

               Tomoaki  YAMAGUCHI

[vat...@litmusautomation.com]

I prefer single topic with JSON { ID, Value, timestamp }

It keeps your data organized.