[rrd-users] gap in graph in case of UNKNOWN value

[Simon Hobson]

Martin T wrote:

>I'm sure it's showing zeros- when the network outage started, HDD
>temperature value went from previous value directly to zero. If I had
>a network outage and server was unreachable to a machine where
>rrdtools runs, following data was written to RRD:
>
># rrdtool fetch HDD.rrd AVERAGE -s 1307061000 -e 1307075400
>                          HDD
>
>1307061600: 2.8986899863e+01
>1307062800: 0.0000000000e+00
>1307064000: 0.0000000000e+00
>1307065200: 0.0000000000e+00
>1307066400: 0.0000000000e+00
>1307067600: 0.0000000000e+00
>1307068800: 0.0000000000e+00
>1307070000: 0.0000000000e+00
>1307071200: 0.0000000000e+00
>1307072400: 0.0000000000e+00
>1307073600: 0.0000000000e+00
>1307074800: 1.0011661112e+01
>1307076000: 3.3748035371e+01

Yes, it's storing zeros.

>If any additional information is needed, please ask!
>
>Am I correct, that in my case there are zeros written to the RRD in
>case of UNKNOWN value? If yes, how to change this behavior?

No, I can assure you that if you write unknown (or don't update at 
all) then you'll get unknown.

So I'll refer you to a question I asked earlier :

>  > Are you sure you are writing unknowns and not zeroes to the database
>  > OR are not writing anything ?

I suggest you need to look at your script and see what it's doing. My 
guess is that you are not correctly handing a lack of response - I 
think you must use the value "U" and not just an empty string. One 
useful technique is to add debugging statements and write data to a 
text file. For example, if your script had something like this :

rrdtool update "${db_file}" "${timestamp}:${value}"

then you coould change that to :

rrdtool update "${db_file}" "${timestamp}:${value}"
echo rrdtool update "${db_file}" "${timestamp}:${value}" >> "${debugfile}"

Perhaps if you posted the relevant bits of your script ?

-- 
Simon Hobson

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