[rrd-users] Re: rrd info fields, averages, maxes, rrdgraph

Tobias Oetiker oetiker at ee.ethz.ch
Wed Feb 7 20:46:44 MET 2001


Today Andres Kroonmaa wrote:

 |
 |
 |  Hi good people,
 |
 |  Can anyone explain to me, why "rrdtool info" shows that 24h average
 |  for given rra is _higher_ than max for same 24h? This seems typical,
 |  but how comes? This looks suspicious.
 |
 |  Second, I understand, that below, rra[4] and rra[5] respectively hold
 |  ds averages and maxes for last 24h. I let rrd graph calculate same
 |  average/max for last 24h, and I get different results. Why?
 |
 |  Also, what does rrd headers ds[dsN].value stand for? I thought they
 |  stand for CF:last (rate from last sample), yet with graph I get again
 |  different results. I don't get it.

the reason for this is (if memory servers correctly) that cdp_prep
area does not hold the same kind of information for AVERAGE as for
MIN and MAX values. For average it holds the SUM of the PDP values
seen sofahr, for MAX and MIN it holds the relevant PDP. When an
average prep_cdp moves into an rra it gets devided by the number of
valid PDPs which went into the sum.

cheers
tobi
 |
 | #rrdtool info fastethernet0_1.rrd
 | filename = "fastethernet0_1.rrd"
 | rrd_version = "0001"
 | step = 300
 | last_update = 981573630
 | ds[ds0].type = "DERIVE"
 | ds[ds0].minimal_heartbeat = 1800
 | ds[ds0].min = 0.0000000000e+00
 | ds[ds0].max = NaN
 | ds[ds0].last_ds = "1902887567"
 | ds[ds0].value = 1.4077733077e+07
 | ds[ds0].unknown_sec = 0
 | ds[ds1].type = "DERIVE"
 | ds[ds1].minimal_heartbeat = 1800
 | ds[ds1].min = 0.0000000000e+00
 | ds[ds1].max = NaN
 | ds[ds1].last_ds = "3766923824"
 | ds[ds1].value = 1.8974612308e+07
 | ds[ds1].unknown_sec = 0
 | rra[0].cf = "AVERAGE"
 | rra[0].rows = 600
 | rra[0].pdp_per_row = 1
 | rra[0].xff = 0.0000000000e+00
 | 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 = 600
 | rra[1].pdp_per_row = 6
 | rra[1].xff = 0.0000000000e+00
 | rra[1].cdp_prep[0].value = 1.8478077248e+06
 | rra[1].cdp_prep[0].unknown_datapoints = 0
 | rra[1].cdp_prep[1].value = 2.5527734670e+06
 | rra[1].cdp_prep[1].unknown_datapoints = 0
 | rra[2].cf = "AVERAGE"
 | rra[2].rows = 600
 | rra[2].pdp_per_row = 24
 | rra[2].xff = 0.0000000000e+00
 | rra[2].cdp_prep[0].value = 7.4878643473e+06
 | rra[2].cdp_prep[0].unknown_datapoints = 0
 | rra[2].cdp_prep[1].value = 1.0403525907e+07
 | rra[2].cdp_prep[1].unknown_datapoints = 0
 | rra[3].cf = "MAX"
 | rra[3].rows = 600
 | rra[3].pdp_per_row = 24
 | rra[3].xff = 0.0000000000e+00
 | rra[3].cdp_prep[0].value = 5.1352932593e+05
 | rra[3].cdp_prep[0].unknown_datapoints = 0
 | rra[3].cdp_prep[1].value = 7.4711004588e+05
 | rra[3].cdp_prep[1].unknown_datapoints = 0
 | rra[4].cf = "AVERAGE"
 | rra[4].rows = 600
 | rra[4].pdp_per_row = 288
 | rra[4].xff = 0.0000000000e+00
 | rra[4].cdp_prep[0].value = 1.2289683591e+08
 | rra[4].cdp_prep[0].unknown_datapoints = 0
 | rra[4].cdp_prep[1].value = 1.8594401140e+08
 | rra[4].cdp_prep[1].unknown_datapoints = 0
 | rra[5].cf = "MAX"
 | rra[5].rows = 600
 | rra[5].pdp_per_row = 288
 | rra[5].xff = 0.0000000000e+00
 | rra[5].cdp_prep[0].value = 9.1094674129e+05
 | rra[5].cdp_prep[0].unknown_datapoints = 0
 | rra[5].cdp_prep[1].value = 1.3906511967e+06
 | rra[5].cdp_prep[1].unknown_datapoints = 0
 |
 |
 | rrdtool graph \
 |  "/dev/null"    \
 |  "DEF:vavg0=fastethernet0_1.rrd:ds0:AVERAGE"       \
 |  "DEF:vmax0=fastethernet0_1.rrd:ds0:MAX"   \
 |  "DEF:vavg1=fastethernet0_1.rrd:ds1:AVERAGE"       \
 |  "DEF:vmax1=fastethernet0_1.rrd:ds1:MAX"   \
 |  "CDEF:savg0=vavg0"        \
 |  "CDEF:smax0=vmax0"        \
 |  "CDEF:savg1=vavg1"        \
 |  "CDEF:smax1=vmax1"        \
 |  "PRINT:savg0:LAST:ds0 lst - %12.1lf" \
 |  "PRINT:savg0:AVERAGE:ds0 avg - %12.1lf"      \
 |  "PRINT:smax0:MAX:ds0 max - %12.1lf" \
 |  "PRINT:savg1:LAST:ds1 lst - %12.1lf" \
 |  "PRINT:savg1:AVERAGE:ds1 avg - %12.1lf"      \
 |  "PRINT:smax1:MAX:ds1 max - %12.1lf"   \
 |  "-s -1day"
 |
 |
 | 0x0
 | ds0 lst -     473262.3
 | ds0 avg -     543408.9
 | ds0 max -    2906656.6
 | ds1 lst -     635394.9
 | ds1 avg -     752755.6
 | ds1 max -    1390651.2
 |
 |
 |
 | ------------------------------------
 |  Andres Kroonmaa <andre at online.ee>
 |  Delfi Online
 |  Tel: 6501 731, Fax: 6501 708
 |  Pärnu mnt. 158, Tallinn,
 |  11317 Estonia
 |
 |
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 |

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