Looks like a race condition with regard to ‘Current’ value.
For example, the RRD ‘buckets’ (step size) may be of size 5min. Thus, they run 12:00-12:05, 12:05-12:10, etc etc If the current time is 12:01, but your data comes in at 12:04, then the ‘current’ value is ‘unknown’ – since there is no data for the current bucket. Not knowing your RRD configuration, heartbeat, step, etc I can’t say for sure, but I have seen this happen many times in RRD graphs. The way around it is to cheat J. You can define a CDEF that uses something like “x,UN,PREV,x,IF” and then use this for your ‘Current’ calculation; though this will hide when a DS is really unknown. Otherwise, if you know the graph is base at ‘now’, and your step is 5 min, then try “NOW,TIME,-,300,LT,x,UN,+,2,EQ,PREV(x),x,IF” This says “If this data point is <5min old, and is unknown, then take the previous value, else take the current value” You may also want to take a look at the ADDNAN function for your sum_in and sum_out instead of all the UN,IF etc. Steve _____ Steve Shipway ITS Unix Services Design Lead University of Auckland, New Zealand Floor 1, 58 Symonds Street, Auckland Phone: +64 (0)9 3737599 ext 86487 DDI: +64 (0)9 923 6487 Mobile: +64 (0)21 753 189 Email: <mailto:s.ship...@auckland.ac.nz> s.ship...@auckland.ac.nz P Please consider the environment before printing this e-mail : 打印本邮件，将减少一棵树存活的机会 From: rrd-users-bounces+s.shipway=auckland.ac...@lists.oetiker.ch [mailto:rrd-users-bounces+s.shipway=auckland.ac...@lists.oetiker.ch] On Behalf Of Stanislav Datskevich Sent: Wednesday, 6 November 2013 4:34 a.m. To: rrd-users@lists.oetiker.ch Subject: [rrd-users] Strange behavior of rrdgraph with data summarization from multiple RRDs by CDEF Hello, list! I've found a strange behavior of rrdgraph when I trying to summarize traffic data from multiple RRDs. I use this CDEF expression to summarize traffic: CDEF:sum_in=in1,UN,0,in1,IF,in3,UN,0,in3,IF,+,in4,UN,0,in4,IF,+,<others>,8,* CDEF:sum_out=out1,UN,0,out1,IF,out3,UN,0,out3,IF,+,out4,UN,0,out4,IF,+,<others>,8,* Point is to check every variable to 'unknown' value and replace it with 0, then sum with previous values, and at last multiple sum by 8 to get bits instead of bytes. Result is very strange: http://noc.nek0.net/configs/graph_good.png shows graph on even minutes (i.e. 14:16 ), http://noc.nek0.net/configs/graph_bad.png shows graph on odd minutes (14:17). Look at the graph legend: it shows now is 0.00 bps traffic. Workaround is to not check first variable in CDEF for unknown, like this: CDEF:sum_in=in1,in3,UN,0,in3,IF,+,in4,UN,0,in4,IF,+,<others>,8,* CDEF:sum_out=out1,out3,UN,0,out3,IF,+,out4,UN,0,out4,IF,+,<others>,8,* With this formula, it will show last value correct regardless of current minute. RRDs updates every minute, at first 2-3 seconds of the minute. Can somebody explain this please? I will appreciate any help. My whole rrdgraph expression also is in attach.
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