Helios Solaris wrote:
>> Over how many days ?
>
> Over the entire database (2 years).
Ouch - as already mentioned by Alex, that could be a LOT of processing and also
prevents you using consolidation.
> Yes, using time shift may work, but it's not really flexible when I want
> to change parameters.
Depends on what you want to change. I would script it so that the parameters
are easy to change - that's how most of my graphs work, passing (eg) start,
end, and step values that are generated by a case statement in a shell script
that takes "day", "week", "month", "year" as a parameter.
I do have another thought ...
How many time periods do you want during the day ? If it's not too many (where
"too many" is somewhat subjective), then you might want to look at turning it
around - store (say) midnight-1am in one rrd file, 1am to 2am in another, and
so on (in this example, using 24 rrd files). Each rrd file can then use
consolidation.
And (I'm sort of typing as my thought process flows here), I'm led to another
option - but which limits consolidation again.
For midnight to 1am, use a time of day function to set a CDEF to the stored
value if the function is true and to either zero or unknown if not. Then
another time function and cdef for 1am to 2am, and so on. Then you can use a
VDEF to get a consolidation across the whole CDEF to get a single value - which
you can then print with a PRINT (not GPRINT) statement.
However, a quick look at the docs suggest that there isn't a simple "time of
day" function which complicates matters somewhat.
I **think** this may do it !
DEF:x=somefile.rrd...
CDEF:tod=TIME,DUP,86400,/,FLOOR,86400,*,-
# get time of sample, divide by 86400 (1 day), take integer part, multiply by
86400 (get time value of midnight at start of day) and subtract from time of
sample to get the number of seconds since midnight.
CDEF:h0=tod,0,GE,x,3600,LT,[0|UNKN],IF,[0|UNKN],IF
# If 0<=tod<3600 then get x else get [0|UNKN]
VDEF:h0ave=h0,AVERAGE
# Get an average value.
PRINT:h0ave,"%6.2lf'
CDEF:h1=tod,3600,GE,x,7200,LT,[0|UNKN],IF,[0|UNKN],IF
and so on ...
This is the sort of thing I'd just script in Bash - almost trivial to generate
an arbitrary number of statements covering appropriate timescales
It's so long since I've used the TIME function, dunno if it should be
tod=TIME... or tod=x,TIME... (ie get x, then get the TIME value for the current
sample.
Whether you use zero or unknown for the times outside of each window depends a
little on your requirements. I suspect that unknown (UNKN) is probably the
correct one to use.
Whatever happens, I don't think you can calculate and graph in one go. You'll
have a "graph" going back an arbitrary time to generate just one day's worth of
data - and I don't think you can have a graph covering (say) 2 years of data
but only drawing a line for one day. Something like gnuplot might be a better
fit for that.
I'd also expect this to be "quite slow" and resource intensive. Lets consider
the case where you do it only by hours. You are creating 1 duplicate of your
dataset with time of day calculated, then another 24 duplicates. So that's
effectively 25 copies of your database in memory at once.
Go down to (say) 5 minute periods, and it then means 289 (1 + 288) copies of
the database in memory at once !
AND you must store all the data you want to use. That means, if you want 5
minute slots for a full 2 years, you need to store 5 minute consolidated data
points for 2 years - that's 210240 samples to store (though I guess that's not
so much data).
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