Using DERIVE, if i remember well, the value is also divided by the time elapsed so for example: 10:24 | 22806 | +41 | 128m | 3.12

41/300 (5 minutes interval)=0,136 and rrd will report that number to a understandable unit (m is milli) so it's 0,136*1000=136m. De difference of the value you get here 128m instead of 136 m should be beacause rrd will calc the time when he get the data so it's like it got the new value after 320 seconds instead of 300 (41/0,128 = 320). The data graphed is something like opens/seconds. The suggestion on the rrd site is to eventually multiply it and get data/minutes or data/hours instead of the "pure" absolute value that is not really useful. To do this you can put a CDEF in the hobbitgraphs

[mysqlopen] DEF:op=mysqlperf.rrd:Opens:AVERAGE CDEF:opm=op,60,* TITLE MySQL Open / Minutes YAXIS open/min LINE2:opm#00CCCC:Open/min. COMMENT:\n GPRINT:slow:LAST: \: %5.1lf (cur) GPRINT:slow:MAX: \: %5.1lf (max) GPRINT:slow:MIN: \: %5.1lf (min) GPRINT:slow:AVERAGE: \: %5.1lf (avg)\n

Just to put the right value in the next version of dbcheck.pl do you know the kind of the other counter? I'm working with mysql on a test db so the perf data are not so clear to understand :D If I'm correct they should be: Threads = GAUGE Questions = DERIVE Slow queries = DERIVE Opens = DERIVE Flush tables = DERIVE Open tables = GAUGE Queries per second avg = GAUGE

Is this correct?

This is the explanation on the rrd create from the website...

It's always a Rate RRDtool stores rates in amount/second for COUNTER, DERIVE and ABSOLUTE data. When you plot the data, you will get on the y axis amount/second which you might be tempted to convert to an absolute amount by multiplying by the delta-time between the points. RRDtool plots continuous data, and as such is not appropriate for plotting absolute amounts as for example ``total bytes'' sent and received in a router. What you probably want is plot rates that you can scale to bytes/hour, for example, or plot absolute amounts with another tool that draws bar-plots, where the delta-time is clear on the plot for each point (such that when you read the graph you see for example GB on the y axis, days on the x axis and one bar for each day).

Francesco

Hello,

I am trying to graph the value of the "Opens" value produced by dbcheck when monitoring mysql.

I defined the value as DERIVE in NCV_mysql instead of GAUGE, as this is a value that is growing while the mysql instance is running (if the mysql instance restart it restarts from 0).

For instance, I have the following:

time | Opens | diff | graph'd | diff/graph'd | value | t'-t | value | value ------+-------+------+---------+------------- 10:14 | 22732 | - | - | - 10:19 | 22765 | +33 | 110m | 3.33 10:24 | 22806 | +41 | 128m | 3.12 10:29 | 22821 | +15 | 50m | 3.33 10:34 | 22835 | +14 | 48m | 3.2

I was expecting the graphed value to be equal to the diff value, but the units are wrong (m instead of unit), and the value is wrong as well (with a somewhat constant 3.xx ratio).

Any idea where this comes from? (I suspect this is me being stupid and not understanding some of the underlying rrd subtleties)

Cheers, Gildas

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