[rrd-users] Strange fetch behaviour (even stranger in the python bindings)

[Dimitris Karteris]

Hi to all,

I'm having some problems with fetch. It just doesn't seem to get things 
right as far as "start" and "end" arguments are concerned. I'm kinda 
newbie in rrdtool so I hope I'm not missing something here. Anyway, here 
goes: I'm trying to fetch some values from an rrd file with step set to 
1. Here's what I get for the 1201849690 to 1201849693 time series:

  $ rrdtool fetch lights_corridor.rrd LAST \
                  -s 1201849690 -e 1201849693
                            main

  1201849691: 0.0000000000e+00
  1201849692: 0.0000000000e+00
  1201849693: 0.0000000000e+00
  1201849694: 0.0000000000e+00

It seems that rrdtool adds a second to both "start" and "end", so I get 
values for the 1201849691 to 1201849694 time series. anyway, using fetch 
from the Python bindings I get even more weird results:

  >>> rrdtool.fetch("lights_corridor.rrd", "LAST", 1201849690,1201849693)
  ((1201849690, 1201849694, 1), ('main',), [(0.0,), (0.0,), (0.0,),
  (0.0,), (-9.5644785903411794e-40,)])
         ^^^^^^^^^^^^^^^^^^^^^^^^^^

This last value seems to have come from nowhere:

  $ rrdtool fetch lights_corridor.rrd LAST \
                  -s 1201849690 -e 1201849696
                            main

1201849691: 0.0000000000e+00
1201849692: 0.0000000000e+00
1201849693: 0.0000000000e+00
1201849694: 0.0000000000e+00
1201849695: 1.0000000000e+00
1201849696: nan
1201849697: nan


And the dump tool says: ::

<!-- Round Robin Database Dump --><rrd> <version> 0003 </version>
         <step> 1 </step> <!-- Seconds -->
         <lastupdate> 1201849695 </lastupdate> <!-- 2008-02-01 09:08:15 
EET -->

         <ds>
                 <name> main </name>
                 <type> GAUGE </type>
                 <minimal_heartbeat> 86400 </minimal_heartbeat>
                 <min> 0.0000000000e+00 </min>
                 <max> 1.0000000000e+00 </max>

                 <!-- PDP Status -->
                 <last_ds> UNKN </last_ds>
                 <value> 0.0000000000e+00 </value>
                 <unknown_sec> 0 </unknown_sec>
         </ds>

<!-- Round Robin Archives -->

[...]
  <cf> LAST </cf>
                 <pdp_per_row> 1 </pdp_per_row> <!-- 1 seconds -->

                 <params>
                 <xff> 5.0000000000e-01 </xff>
                 </params>
                 <cdp_prep>
                         <ds>
                         <primary_value> 1.0000000000e+00 </primary_value>
                         <secondary_value> 0.0000000000e+00 
</secondary_value>
                         <value> NaN </value>
                         <unknown_datapoints> 0 </unknown_datapoints>
                         </ds>
                 </cdp_prep>
                 <database>
                         <!-- 2008-01-25 09:08:16 EET / 1201244896 --> 
<row><v> NaN </v></row>
                         <!-- 2008-01-25 09:08:17 EET / 1201244897 --> 
<row><v> NaN </v></row>

[...]

<!-- 2008-02-01 09:08:10 EET / 1201849690 -->
<row><v> 0.0000000000e+00 </v></row>
<!-- 2008-02-01 09:08:11 EET / 1201849691 -->
<row><v> 0.0000000000e+00 </v></row>
<!-- 2008-02-01 09:08:12 EET / 1201849692 -->
<row><v> 0.0000000000e+00 </v></row>
<!-- 2008-02-01 09:08:13 EET / 1201849693 -->
<row><v> 0.0000000000e+00 </v></row>
<!-- 2008-02-01 09:08:14 EET / 1201849694 -->
<row><v> 0.0000000000e+00 </v></row>
<!-- 2008-02-01 09:08:15 EET / 1201849695 -->
<row><v> 1.0000000000e+00 </v></row>
                 </database>
         </rra>
</rrd>

I've made my test with both versions 1.2.19 (default in Ubuntu gutsy) 
and 1.2.26 having the same exact results. Can anybody please shed some 
light here? Is this a bug or am I getting something completely wrong?

Thank you in advance,

~dkart