Everyone knows that MRTG needs at least one value to be passed on it's input.
In per-target options MRTG has 'gauge', 'absolute' and default (with no options) behavior of 'what to do with incoming data'. Or, how to count it.
Lets look at the elementary, yet popular example :
We pass cumulative data from network interface statistics of 'how much packets were recieved by the interface'.
We take it from '/proc/net/dev' or look at 'ifconfig' output for certain network interface. The number of recieved bytes is increasing every time. Its cumulative.
So as i can imagine there could be two types of possible statistics:
1. How fast this value changes upon the time interval. In oher words - activity.
2. Simple, as-is growing graphic that just draw every new value per every minute (or any other time interwal)
First graphic will be saltatory (activity). Second will just grow up every time.
I read twice rrdtool's and MRTG's docs and can't understand which option mentioned above counts what.
I suppose (i am not sure) that 'gauge' draw values as is, without any differentiation calculations (good for measuring how much memory or cpu is used every 5 minutes). And default or 'absolute' behavior tryes to calculate the speed between nearby measures, but what's the differencr between last two?
Can you, guys, explain in a simple manner which behavior stands after which option of three options possible?
Thanks in advance.
MRTG assumes that everything is being measured as a rate (even if it isnt a rate)
Type 'gauge' assumes that you have already calculated the rate; thus, the provided value is stored as-is (after Data Normalisation). This is appropriate for things like CPU usage.
Type 'absolute' assumes the value passed is the count since the last update. Thus, the value is divided by the number of seconds since the last update to get a rate in thingies per second. This is rarely used, and only for certain unusual data sources that reset their value on being read - eg, a script that counts the number of lines in a log file, then truncates the log file.
Type 'counter' (the default) assumes the value passed is a constantly growing count, possibly that wraps around at 16 or 64 bits. The difference between the value and its previous value is divided by the number of seconds since the last update to get a rate in thingies per second. If it sees the value decrease, it will assume a counter wraparound at 16 or 64 bit. This is appropriate for something like network traffic counters, which is why it is the default behaviour (MRTG was originally written for network traffic graphs)
Type 'derive' is like 'counter', but will allow the counter to decrease (resulting in a negative rate). This is not possible directly in MRTG but you can manually create the necessary RRD if you want.
All types subsequently perform Data Normalisation to adjust the timestamp to a multiple of the Interval. This will be more noticeable for Gauge types where the value is small than for counter types where the value is large.
For information on this, see Alex van der Bogaerdt's excellent tutorial
Related
Good day!
Please, help me understand how the Delay block works in AnyLogic. Suppose we deal with a multichannel transmission network.
The model has 2 sources. Suppose these sources generate packets every 1 sec. Packets from different sources have different priorities and need different quantities of resources to be served (it is set up with Priority and Resource_quantity parameters respectively). The Priority_queue in the model is priority-based. The proposed model put the packets into the channels in accordance with Resource availability in the channel. Firstly, it tries to put the packet to the first channel. If there are no available resources it puts the packet into the second channel. If there are no resources in both channels it waits (it is realized with Hold block).
I noticed that if I set delays in blocks delay1 and delay2 with static parameters (for ex. 2 sec) the model works ok. But then I try to calculate it before these blocks the model doesn't take into consideration it at all. And in this case, the model works without any delays.
What did I do wrong here?
I will appreciate any help.
The delay is calculated in Exit block and is written into the variable delay of the agent. I tried to add traceln(agent.delay) as #Jaco-Ben suggested right after calculation of the delay and it showed zero. In this case it doesn't also seize resources :(
Thank #Jaco-Ben for the useful comments.
The delay is zero because
the result of division in Java depends on the types of the operands.
If both operands are integer, the result will be integer as well. To
let Java perform real division (and get a real number as a result) at
least one of the operands must be of real type.
So it was my problem.
To solve it I assigned double to one of the operands :
agent.delay = (double)agent.Resource_quantity/ChannelResources1.idle();
However, it is strange why it shows correct values in the database.
Is it possible to SET the interface statistics in Linux after it's been brought up? I'm dealing with rrdtool (mrtg) that gets upset by a daily ifdown and ifup which brings the interface counters back to zero. Ideally I would like to continue counting from where I left and setting the interface values to what they were before the interface went down seems to be the easiest path.
I checked writing to /sys/class/net/ax0/statistics/rx_packets but that gives a Permission Denied error.
netstat, ifup, ifconfig and friends don't seem to support changing these values either.
Anything else I can try?
You can't set the kernel counters, no - but do you really need to?
MRTG will usually graph a rate, based on the difference between samples. So your MRTG/RRD will store packets-per-second values every cycle (usually 5min but maybe 1min). When your device resets the counters, then MRTG will see the value apparently go backwards - which will be discounted as out of range, so one failed sample. But, the next sample will work, and a new rate be given.
If you're getting a big spike in the MRTG graph at the point of the reset, this will be due to an incorrect 'counter rollover' detection. You can prevent this by either setting the MRTG AbsMax setting (to prevent this high value from being valid) or (better) by using SNMPv2 counters (where a reset is more obvious).
If you set your RRD file to have a large enough heartbeat and XFF, then this one missing sample will be interpolated, and so your graphs (which, remember, show the rate rather than the total) will continue to look fine.
Should you need the total, it can be derived by sum(rate x interval) which is automatically done by the Routers2 frontend for MRTG/RRD.
I want to use snd_pcm_delay() to query the delay until the sample I am about write to the ALSA buffer are hearable. I expect this value to vary between individual calls. Though, on two system this value is constant. The function returns a value that is always equal to the period size on one platform and on the other platform it is equal to the buffer size (two times the period size in my code).
Is my understanding of snd_pcm_delay() wrong? Is it a driver problem?
The delay is proportional to the number of samples in the buffer (the inverse of snd_pcm_avail()), plus a time that describes how much time is needed to move samples from the buffer to the speakers. The latter part is driver dependent and might not be implemented.
If the device takes out samples one entire period at a time (some DMA controllers have no better granularity for reporting the current position), then the delay value will appear to stay constant for a time, and then jump by an entire period. And you see that jump only before you have re-filled the buffer.
This is an interview question:
Say that you have an infinite amount of sorted data coming in, implement a way to find a specific time stamp.
What I can think of is to keep the data in a log file or something like that and use the sed command to find the log entry of that specific time stamp.
I do not know if what I think is correct or not.
Other solutions?
This seems like an open-ended question. Your solution was to keep the data in a log file, but with an infinite amount of data, you would then need an impractical amount of disk space as well. The problem is probably supposed to be analyzed in the following manner.
At first glance, with an infinite stream of data coming in, it is not stated what the rate of its coming is. Assuming the rate is r every second and you can check only n timestamps every second. It is not very interesting if r <= n.
If r > n you can only check one in every r/n integers. Then, that means you need to maintain a buffer of size r/n. The fact that the input is sorted implies that you can check the ends of the buffer and see if the desired timestamp is in range. If it is, you go through your buffer and identify the required timestamp.
Interview tip: It is often that these questions are open-ended in order to judge your thought processes. If it is underspecified (like it is here), you should ask for clarification.
I have the following problem:
I want to do the statistics of data that need to be constantly increasing. For example, the number of visits to the link. After some time be restarted these visit and start again from the beginning. To have a continuous increase, want to do the statistics somewhere. For this purpose, use a site that does this. In his condition can be used to COUNTER, GAUGE, AVERAGE, ... a.. I want to use the COUNTER. The system is built on Nagios.
My question is how to use this COUNTER. I guess it is the same as that of the RRD. But I met some strange things in the creation of such a COUNTER.
I submit the values ' 1 ' then ' 2 ' and the chart to come up 3. When I do it doesn't work. After the restart, for example, and submit again 1 to become 4
Anyone dealt with these things tell me briefly how it works with this COUNTER.
I saw that the COUNTER is used for traffic on routers, etc, but I want to apply for a regular graph, which just increases.
The RRD data type COUNTER will convert the input data into a rate, by taking the difference between this sample and the last sample, and dividing by the time interval (note that data normalisation also takes place and this is dependent on the Interval setting of the RRD)
Thus, updating with a constantly increasing count will result in a rate-of-change value to be graphed.
If you want to see your graph actually constantly increasing, IE showing the actual count of packets transferred (for example) rather than the rate of transfer, you would need to use type GAUGE which assumes any rate conversion has already been done.
If you want to submit the rate values (EG, 2 in the last minute), but display the overall constantly increasing total (in other words, the inverse of how the COUNTER data type works), then you would need to store the values as GAUGE, and use a CDEF in your RRDgraph command of the form CDEF:x=y,PREV,+ to obtain the ongoing total. Of course you would only have this relative to the start of the graph time window; maybe a separate call would let you determine what base value to use.
As you use Nagios, you may like to investigate Nagios add-ons such as pnp4nagios which will handle much of the graphing for you.