[rrd-developers] Re: bug - no way to retrieve an RRA that is a multiple of another

[Jo Rhett]

Okay, I found the bug.  The problem is that partial matches were  
resetting the 'best_step_diff' value.  Using debug showed this:
bash-3.00# ./rrdtool fetch /d/rrd/stats/bd/metro2.5.7.rrd AVERAGE -e  
22:00 -s end-168h -r 1800 2>&1 | head -10
Entered rrd_fetch_fn() searching for the best match
Looking for: start 1140069600 end 1140674400 step  1800
Considering: start 1137221100 end 1140677100 step    60 best full  
match so far
Considering: start 1139236200 end 1140676200 step  1800 best full  
match so far
Considering: start 1134914400 end 1140674400 step  7200 full match,  
not best
Considering: start 1071532800 end 1140652800 step 86400 best partial  
so far
Considering: start 1133765100 end 1140677100 step   300 best full  
match so far
We found:    start 1140069600 end 1140674400 step   300 rows  2017

What was happening was that the partial match of 86400 reset the  
best_step_diff, and then the 300 full match was a closer  
differential.  Careful ordering of the RRAs in the RRD file would not  
see this problem.  However, the patch was simple -- have  
best_full_step_diff and best_part_step_diff.  A patch is attached,  
and it works perfectly with everything I can see.


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