[rrd-users] how to fill with previous value when graph

[ekgnkb3d]

Hi all,
is this still the best solution to solve this problem? Maybe after almost 7
years something different is possible....

Also in my case, a gap filled by a longer heartbeat shall have the last
entered rate (fill forward) instead of the default behavior to insert the
new rate in all older nan's (fill backward). 
The last rate is valid until a newer rate updates it.

Thanks a lot
  Achim


Alex van den Bogaerdt-2 wrote:
> 
> On Thu, May 15, 2003 at 08:14:47AM -0400, Dan McGinn-Combs wrote:
> 
> RRDtool always updates data *after* it happened.
> This means if the rate is "x" and if you didn't set the previous
> three intervals and if the "heartbeat" setting allows for it, all
> previous intervals will be set to the current rate "x".
> 
> If this is undesired behaviour, the front end has to remember the
> "correct" rate (or fetch it from the database) and use that rate
> to set the previous but not current interval.
> 
> 1	defined by an "rrdtool update" call with rate "a"
> 2	defined by an "rrdtool update" call with rate "b"
> 3	defined by an "rrdtool update" call with rate "c"
> 4	not yet defined
> 5	not yet defined
> 6	not yet defined
> 
> Now, if interval 6 is going to be defined (rate "d") and if the
> heartbeat allows for it, intervals 4,5 and 6 will be set to rate "d".
> 
> This is undesired, then do:
> 
> -1- find the last known rate "c"
> -2- update intervals 4 and 5 with rate "c"
> -3- update interval 6 with rate "d"
> 
> Step (2) will have to be done using "rrdtool update 12345:"... where
> 12345 is the appropriate time stamp.
> 
> Step (1) can be done by remembering the last value given to rrdtool
> (the easy way) or by querying rrdtool using "rrdtool fetch" (this is
> the hard way).
> 
> A similar (in fact: the same) problem has been discussed many moons
> ago; it had to do with modem lines in use.  Google is your friend.
> 
> 
> The story is completely different if the user wants to *graph* this
> data (without doing the actual update as described above):
> 
> 1	defined by an "rrdtool update" call with rate "a"
> 2	defined by an "rrdtool update" call with rate "b"
> 3	defined by an "rrdtool update" call with rate "c"
> 4	not yet defined
> 5	not yet defined
> 6	not yet defined
> 
> If the graph should include intervals 1 through 6, I don't see
> how this can be done without a very complex CDEF, if at all possible.
> Doing so would mean rrdtool should graph unknown data as if it wasn't
> unknown.  
> 
> Alex
> 
> 

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