[rrd-users] BUG in "RRA:MAX:0.5:6:700"

[Rui Vitor Figueiras Meireles]

I noticed a problem in my RRDs. I several RRD files, running RRDtool 1.2.19 in Solaris 10:

I use:

 *   GAUGE RRDs
 *   300sec step
 *   RRA with 1 PDP/ROW for AVERAGE
 *   RRA with 1 PDP/ROW for MAX
 *   RRA with 6 PDP/ROW for AVERAGE
 *   RRA with 6 PDP/ROW for MAX
(the info of the RRD is listed below)

I always update the values using "rounded times" (times that are multiple of 300).
However, some consecutive values of my rra[3] (MAX - 6 values) appeared exactly the same value (and I thought it was very odd).

I did the "rrdtool fetch", I did all the maths, and realized that this wasn't doing what I supposed it should be!

AVERAGE uses the last 6 values for the calculation
but
MAX uses the last 7 values for the calculation

Ex:

AVERAGE (6 values)

rra[1](1268674200) = AVERAGE (
rra[0](1268672700),
rra[0](1268673000),
rra[0](1268673300),
rra[0](1268673600),
rra[0](1268673900),
rra[0](1268674200)
)
rra[1](1268676000) = AVERAGE (
rra[0](1268674500),
rra[0](1268674800),
rra[0](1268675100),
rra[0](1268675400),
rra[0](1268675700),
rra[0](1268676000)
)

MAX (7 values)

rra[3](1268674200) = MAX (
rra[2](1268672400),
rra[2](1268672700),
rra[2](1268673000),
rra[2](1268673300),
rra[2](1268673600),
rra[2](1268673900),
rra[2](1268674200)
)
rra[3](1268676000) = AVERAGE (
rra[2](1268674200),
rra[2](1268674500),
rra[2](1268674800),
rra[2](1268675100),
rra[2](1268675400),
rra[2](1268675700),
rra[2](1268676000)
)

Now my questions is: Is this a Bug, or a feature?
If it is a feature it's very strange, because whenever I get a high value in a rounded time (multiple of 300) that value will become the MAX of the 2 consecutive groups in the RRA that consolidates 6 values. How is this helpful?


I hope I could make myself clear. If not, I can send a XLS file with my calculations, so that you can see this systematic error.
Thanks in advance to anyone that can answer me.

Rui Meireles


# rrdtool info TOTAL.rrd
filename = "TOTAL.rrd"
rrd_version = "0003"
step = 300
last_update = 1268853900
ds[in].type = "GAUGE"
ds[in].minimal_heartbeat = 600
ds[in].min = 0.0000000000e+00
ds[in].max = 5.0000000000e+11
ds[in].last_ds = "307502466.241261"
ds[in].value = 0.0000000000e+00
ds[in].unknown_sec = 0
ds[out].type = "GAUGE"
ds[out].minimal_heartbeat = 600
ds[out].min = 0.0000000000e+00
ds[out].max = 5.0000000000e+11
ds[out].last_ds = "8028989485.28258"
ds[out].value = 0.0000000000e+00
ds[out].unknown_sec = 0
rra[0].cf = "AVERAGE"
rra[0].rows = 600
rra[0].pdp_per_row = 1
rra[0].xff = 5.0000000000e-01
rra[0].cdp_prep[0].value = NaN
rra[0].cdp_prep[0].unknown_datapoints = 0
rra[0].cdp_prep[1].value = NaN
rra[0].cdp_prep[1].unknown_datapoints = 0
rra[1].cf = "AVERAGE"
rra[1].rows = 700
rra[1].pdp_per_row = 6
rra[1].xff = 5.0000000000e-01
rra[1].cdp_prep[0].value = 1.5398389100e+09
rra[1].cdp_prep[0].unknown_datapoints = 0
rra[1].cdp_prep[1].value = 5.2927918671e+10
rra[1].cdp_prep[1].unknown_datapoints = 0
rra[2].cf = "MAX"
rra[2].rows = 600
rra[2].pdp_per_row = 1
rra[2].xff = 5.0000000000e-01
rra[2].cdp_prep[0].value = NaN
rra[2].cdp_prep[0].unknown_datapoints = 0
rra[2].cdp_prep[1].value = NaN
rra[2].cdp_prep[1].unknown_datapoints = 0
rra[3].cf = "MAX"
rra[3].rows = 700
rra[3].pdp_per_row = 6
rra[3].xff = 5.0000000000e-01
rra[3].cdp_prep[0].value = 3.1016264837e+08
rra[3].cdp_prep[0].unknown_datapoints = 0
rra[3].cdp_prep[1].value = 1.2197452159e+10
rra[3].cdp_prep[1].unknown_datapoints = 0



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