[rrd-developers] (bug?) Incorrectly selecting low-res RRA

Wed Mar 26 11:24:49 MET 2003

Hi all,

Firstly, this is partly a repost from the users list; apologies if it's 
already being investigated, but I have additional information...

In some circumstances, rrd fetch is definitely picking up a lower 
resolution RRA than during the rest of the time.  Following my surprise 
discovery of this below, I put in a cron job piping the output of an rrd 
fetch to wc -l to check how many entries it returned every minute.  Sure 
enough, although it returned 244 (or occassionally 243) lines nearly all 
the time, for a period (eg. starting one minute after midnight last 
night, for 24 minutes) it only returns 32 lines.

The output of rrd info for that rrd is included in the below.  Exactly the 
same thing seems to happen for several hundred rrds (all created with the 
same structure, although at many different times, and updated 
independently).

I'd be very grateful for any information on why this might happen and what 
I might do about it!

Thanks,
Phil

== Original message (Sun, 23 Mar 2003) =====================================
I'm suddenly getting a situation where rrdtool is picking up a 
low-resolution RRA instead of the one it used to use - I can't spot 
anything that has changed since it last worked, so I'm a little confused.

I'm using 1.0.41 - the same problem started in 1.0.40, and I've just 
upgraded because the entry 'fix borderline problem with rrd_fetch 
selecting the wrong rra under certain conditions' in the changelog seemed 
relevant!

I'm using ganglia (http://ganglia.sourceforge.net/) to populate my RRDs, 
and have RRAs for hour/day/week/month/year/decade - see an example output 
from rrdtool info below.  When plotting the monthly graphs, it should be 
using 240 datapoints; however, it's suddenly switched to just thirty - see 
sample output from rrdtool fetch below.  And this is consistent across 
every graph I'm plotting.

Ah - it gets more entertaining; it all works again now.  And I definitely 
didn't change anything!  The window of bad behaviour was maybe an hour 
(and I'm not normally looking at these graphs at this time of day/week!)

Is it possible there's another bug along the lines of the one fixed in the 
changelog entry mentioned above?  Is there anything I can do to help 
narrow down the problem?

Thanks for any help!
Phil

=== sample rrdtool info ===
> filename = "transfers.rrd"
> rrd_version = "0001"
> step = 15
> last_update = 1048379989
> ds[sum].type = "GAUGE"
> ds[sum].minimal_heartbeat = 30
> ds[sum].min = NaN
> ds[sum].max = NaN
> ds[sum].last_ds = "UNKN"
> ds[sum].value = 0.0000000000e+00
> ds[sum].unknown_sec = 0
> rra[0].cf = "AVERAGE"
> rra[0].rows = 240
> 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[1].cf = "AVERAGE"
> rra[1].rows = 240
> rra[1].pdp_per_row = 24
> rra[1].xff = 5.0000000000e-01
> rra[1].cdp_prep[0].value = 0.0000000000e+00
> rra[1].cdp_prep[0].unknown_datapoints = 0
> rra[2].cf = "AVERAGE"
> rra[2].rows = 240
> rra[2].pdp_per_row = 168
> rra[2].xff = 5.0000000000e-01
> rra[2].cdp_prep[0].value = 0.0000000000e+00
> rra[2].cdp_prep[0].unknown_datapoints = 0
> rra[3].cf = "AVERAGE"
> rra[3].rows = 240
> rra[3].pdp_per_row = 672
> rra[3].xff = 5.0000000000e-01
> rra[3].cdp_prep[0].value = 2.2533333333e+01
> rra[3].cdp_prep[0].unknown_datapoints = 0
> rra[4].cf = "AVERAGE"
> rra[4].rows = 370
> rra[4].pdp_per_row = 5760
> rra[4].xff = 5.0000000000e-01
> rra[4].cdp_prep[0].value = 0.0000000000e+00
> rra[4].cdp_prep[0].unknown_datapoints = 0
> rra[5].cf = "AVERAGE"
> rra[5].rows = 370
> rra[5].pdp_per_row = 17280
> rra[5].xff = 5.0000000000e-01
> rra[5].cdp_prep[0].value = 5.9533333333e+02
> rra[5].cdp_prep[0].unknown_datapoints = 6
> rra[6].cf = "AVERAGE"
> rra[6].rows = 370
> rra[6].pdp_per_row = 57600
> rra[6].xff = 5.0000000000e-01
> rra[6].cdp_prep[0].value = 5.4878666667e+03
> rra[6].cdp_prep[0].unknown_datapoints = 7471

=== sample broken rrdtool fetch ===
> $ rrdtool fetch transfers.rrd AVERAGE -s -2419200 -e N
>                       sum
> 
> 1045958400: nan
> 1046044800: nan
> 1046131200: nan
> 1046217600: nan
> 1046304000: nan
> 1046390400: nan
> 1046476800: nan
> 1046563200: nan
> 1046649600: nan
> 1046736000: nan
> 1046822400: nan
> 1046908800: nan
> 1046995200: nan
> 1047081600: 1.8783181554e-01
> 1047168000: 5.7869212963e-01
> 1047254400: 5.2446759259e-01
> 1047340800: 7.0638888889e-01
> 1047427200: 1.6115046296e+00
> 1047513600: 2.6965277778e+00
> 1047600000: 1.9215046296e+00
> 1047686400: 8.6528671653e-01
> 1047772800: 7.7846064815e-01
> 1047859200: 6.6748842593e-01
> 1047945600: 1.3293171296e+00
> 1048032000: 2.7433796296e+00
> 1048118400: nan
> 1048204800: nan
> 1048291200: 9.3993055556e-02
> 1048377600: 9.3731896652e-03
> 1048464000: nan

=== sample working rrdtool fetch ===
> $ rrdtool fetch transfers.rrd AVERAGE -s -2419200 -e N
>                       sum
> 
> 1045961280: nan
> 1045971360: nan
> 1045981440: nan
> 1045991520: nan
> 1046001600: nan
> 1046011680: nan
> 1046021760: nan
> 1046031840: nan
> 1046041920: nan
> 1046052000: nan
> 1046062080: nan
> [...snip lots here, rather than post 240 lines of stuff...]
> 1048269600: 0.0000000000e+00
> 1048279680: 0.0000000000e+00
> 1048289760: 0.0000000000e+00
> 1048299840: 0.0000000000e+00
> 1048309920: 0.0000000000e+00
> 1048320000: 1.1706349206e-02
> 1048330080: 0.0000000000e+00
> 1048340160: 1.7460317460e-02
> 1048350240: 6.4484126984e-03
> 1048360320: 5.5555555556e-03
> 1048370400: 5.5555555556e-03
> 1048380480: 3.3531746032e-02
> 1048390560: nan

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