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