Theoretically, it is possible to control the start and stop values of the X and Y axis. I already read that the MIN and MAX values are important. When the "*" sign is reached, those two numbers are removed from the stack and multiplied. And, the graphs are rather limited. RRD in RRDtool stands for Round Robin Database. I think I mastered the tool, but only after many hours of toil. DESCRIPTION. The RRDs::times function takes two parameters: a "start" and "end" time. If specified, Unless, I did not hit on the correct solution, I can only conclude that you can only use one variable in the "rpn" calculation. Only code lines 9,10, 16, and 17 are new. See the rrdfetchdocumentation for a detailed explanation on how to specify time. It works like this: If you want to store 1'000 values in 5 minute interval, RRDtool will allocate space for 1'000 data values and a header area. The next piece of data goes into the second car and the wheel turns again. Please feel free to link to my blog, but if you wish to copy, directly, from my blog please contact me first through a comment. If you see this text, this means that your browser does not support CSS2. The function graph has one mandatory parameter and 35 optional ones with default values. The graph above illustrates plotting useful solid areas. … And, it illustrates the use of the IF statement to make decisions, in Reverse Polish Notation. Here the calculation is "66,Sen1data,GT,0,Sen1data,IF". fetching values from rrd file. As far as I can see, that is its only advantage. I have included seven of the 35 here. Line 2 is new. In other words, the X axis should be time. We will go through this in detail: Remember, back in the introduction, I mentioned the time in the database looks like 1378241580. See the rrdcreate documentation on the RRDtool website. We also add a few items. Or if some pictu They live in different time zones.Please look this up elsewhere if you want to know details; wikipediawill do a good job, amongst others that I didn't verify. The times in the database are still at the 300 seconds, exact, interval. The calculation is defined in the "rpn" parameter. SYNOPSIS. This is explained on my RRDtool - Rates, normalizing and consolidating page. The GraphXGrid function documentation basically said it is difficult to change the grid. Lines 56 through 87 illustrate how we would report the measurement data. For every point in the database we compare the database value (in Sen1data) to the number 66. My real intention was not to use a discrete value like 66. In my graphic "Computing the Values In the Database", I indicated where the value in the database (black numbers) come from, but not the rational for why the various mechanisms for computation were used. I use rrdtool 1.4.8. that your browser does not support CSS2. If the result 1s 0, the final result is the database value. unexpected results, and pitfalls along the way. The following code sends measurements 100 seconds after the 300 second interval: We notice three things: One, the times in the database do not equal the times that we sent to the database. In this case, it is AVERAGE, which is the "cf" parameter. The comments must be the final item in the list because comments are included at the very bottom. mais quand tu regarde sur la photo la tu vois downoad nan o/s bon j'essaye de changer ça pour voir je te dit quoi édit : quand je tappe rrdtool fetch cpu.rrd AVERAGE --start now-10000 --end now Go to the. It establishes the order of what is drawn on the graph. Python Forums on Bytes. If you do not know or care about min and max, set > them to U for unknown. Thank you. res are missing, then the mirror may not have picked up the contents of the inc directory. rrdtool lastupdate filename [--daemon|-d address]. In this case, again, if 66 is greater than the database value, the result is 1, otherwise 0. There are many forum posts about this Fetch problem dating back to 2009, but there has not been a solution. *UNKNOWN* data is often represented by the string … A few years ago, the extension was patched so that it would count options itself. If 66 is greater than the database value, the result is 1, otherwise, 0. Most of the changes are shown in the code following the graph. I could not get this to function. If the value is exactly 66, it will print green. Embed Embed this gist in your website. My Cacti installation gives only nan values. Address of the rrdcached daemon. Stuff breaks if you don't, so don't. Back in June and July I presented a series of posts titled, "A Raspberry Pi Thermometer". If it were me doing the plotting, I would connect two adjacent data points with one line that slants from one point to the next. Therefore, the resolution == 900. While you can write shell scripts to make your work reusable, I wanted to run it within my python programs. Sometimes you do not want to know the rate (how many bytes per second), you just want to know the total amount of bytes. Line 18 rounds off the number of seconds to the nearest minute. But for me, it's buggy (it does not work with more than 3 arguments) and neither does work. Next, finding the "IF" at the end, it says that if the value is 1, the result of the calculation is the database value, otherwise it is 0. Once you have PyRRD installed you need to know the functions available to you and what parameters can be passed into those functions. Butmost of you will find the information presented here more than enough. We will look at the calculations in the "rpn" parameters. I followed the instructions in the section labeled "Python Bindings". See lines 33 and 34 for sensor 1. Now, if all my measurements were multiples 300, the values in the database matched what I put in. The next value in the database is truly the average of the second and third measurements. In addition, if we are talking about our example, the host we are pinging can be unreachable for some time. For a list of accepted formats, Here is the results: You would have thought the first value in the database would have been the average of the first two measurements. If you see this text, this means rrdtool fetch subdata.rrd AVERAGE -r 15m -s -1h. This is the number of measurements you will take before you enter a value into the database. In addition, it has 35 parameters with default values, so you only have to assert the ones you wish to change. Perhaps you will average each hours worth and graph 24 points, one for each hour in the day. If I take a measurement now (September 3, 2013, 4:53:19 PM), the time in the database would be 1378241580. home > topics > python > questions > fetching values from rrd file Post your question to a community of 467,080 developers. The parameter "rows" controls the number of values you can record before filling the database. In my example, I have chosen every minute or every 60 seconds. The wheel has a limited number of cars. I added some data and from the command line I used the fetch command to see exactly what wound up in the database. I also configured one with "steps" as 2, and consolidation function as AVERAGE. I was developing a small JSP to show the last values for certain metrics and I found that when calling rrdDao.getLastFetchValue(attribute, 300000), I get the following exception: NAME. If you were averaging three values and one was unknown, you will only average two values. In addition to the PyRRD website, please see the. This automatically limits the history to the last 1'000 values (in our example). Please make sure you understand how RRDtool normalizes and consolidates its data. Note the "start" time is one minute before the first measurement is reported. Consider upgrading to a standard conformant kaf3773. So what's a Round Robin Database, and why use one? fetching values from rrd file. Sensor 1 and sensor 2, so far have the same information except each has its own database file name. Further data overwrites the oldest data. As it turned out when asking in the rrdtool-users mailing list, fetch looks more at the number of points you are asking more than the resolution. Each archive becomes an element in a list. The data here, which represents temperature measurements from two sensors, is entirely contrived. I am blogging about this because I find this tool useful. RRDTool keeps track of the last timestamp and calculates a weight for every incoming data point based on time since last update or beginning of the step and the step length. Please feel free to supply a little insight here. With the Debian distribution those files are in: Let's jump in by showing the code that produced the sample graph in the beginning of this post. I want to share what I learned with the Raspberry Pi community. If min and/or max any value outside the defined range will be > regarded as *UNKNOWN*. The order of the items in the list is important. This allows rrdtool to return fresh data even if the daemon is configured to cache values for a long time. Some characters have to be escaped with the "\" character. The graphical This controls, along with the data source type, what values are actually stored in the database. Finally, I really wish I could have changed the Y axis and have it start from some other value besides 0. There is a good solution, and that is a program called PyRRD 0.1.0 which is a python interface to RRDtool. VDEF has two parameters, like CDEF: vname and rpn. time. There is one function of PyRRD that does not work and that is the function called Fetch. It seems to have all the functionality of RRDtool. Consider now that you want to fetch the 15 minute average data for the last hour. rrdtool fetch filename.rrd LAST --start 999999700 --end 1000004500. These should be specified in the AT-STYLE TIME SPECIFICATION format used by RRDtool. Let's look at "66,Sen1data,GT,Sen1data,0,IF" and see what is going on. Provided by: rrdtool_1.4.7-1_amd64 NAME rrdfetch - Fetch data from an RRD. If you have many, many data points, the horizontal lines become very short and the graph looks better. Anyway, it's not too bad. The "Graph" function has only one parameter you must supply, and that is the name of the graph file. Many people use "N", which means "now". The fetch function is normally used internally by the graph function to get data from RRD s. fetch will analyze the RRD and try to retrieve the data in the resolution requested. The format of the BufferValue parameters is "time, measurement". AVERAGE: Take the average value of those measurements. For brevity, I've only shown the changes to sensor 1. It may be 12:00 for both, but then it's going to be 12:00amfor one and 12:00pm for the other. The next code, sends measurements at times either on, before, or after the exact interval. This information can be gleaned from two python files. Embed. Line 17 computes the total number of seconds, including a decimal component, since Jan. 1, 1970. $ rrdtool update datafile.rrd time_t:value You MUST always feed values in chronological order. There are four consolidation functions available. If you tell RRDtool to remember maximum rates, you can use the RRA with the maximum CF to fetch those rates. Picture something round, like a Ferris Wheel, for example. ds1a – The vname is a virtual name for the retrieved data for later use. My Experiences With the Raspberry Pi -- Tracking My Learning -- My Pi Projects. RRDtool is a command line program. As it is, since I reduced some of the sensor 2 values, below sensor 1 values, four of the sensor 2 values are lost. Note that min and max always refer to the processed > values of the DS. My sample graph uses this Round Robin Archive, not the one where I average two measurements. There is one measurement that falls right on the heartbeat definition, and one measurement after the heartbeat. Time depends (mostly) on the position of the sun in thesky. If so desired, you can also define variables containing useful information such as maximum, minimum etcetera. Now, if there is new data, it replaces the data already in the car. Stay tuned. I'm not too sure about the xff parameter. These three instructions extract data values out of the RRD files, optionally altering them (think, for example, of a bytes to bits conversion). So far we have looked at "perfect data". This process is continued. We do this rpn calculation from left to right. I take two measurements, take the average of the two and only report the average in the database. If we were taking measurements every 5 minutes, line 18 would be: Before we add any data we have to create the structures for the databases. That is not always the case. Notice also that the space must be escaped in the "vertical_label" and in the "title". Let's try to analyze how RRDtool decides what values to put into the database. Here is what the same sequence of points looks like in RRDTool. Next we will set up one or more Round Robin Archives. It's no big deal issuing fetch from the command line. Notice, in line 3, that plots the line of data, defObj now refers sen1_cdef not sen1_def. Line 16 gives the UTC time, of right now. There are many idiosyncrasies. For example, if a measurement is taken now, and the heartbeat is 90 seconds, if another measurement is not reported for more than 90 seconds, the next value is reported as "UNKNOWN". If you put GPRINT or COM variables earlier in the list you will throw an exception. People on opposite sides of the globe will disagree on being daytime or night. It seems that whatever you do to the data, and the measurement times, the first value in the database is always going to the the first measurement. Eventually, the first car comes around again. dizeee / rrd-last-value. But, no, it is the first measurement. The following environment variables may be used to change the behavior of rrdtool lastupdate: If this environment variable is set it will have the same effect as specifying the --daemon option on the command line. PyRRD 0.1.0 is not in the Debian depository so you can't use apt-get command to get the program. As I discuss this tool, it will be apparent that it was designed for that purpose. New values are written to the Round Robin Archive in, you guessed it, a round robin manner. What I got was a plot that was red from time 0 to time 11:50. Before I figured out the "\ ". You can see that only between 11:50 and 11:59 will the values be below 66. Consider upgrading to a standard conformant browser like Mozilla Firefox or Opera but also Apple's Safari or … filename. Therefore, the database value and the number 32 go on the stack. Take a look at the sample graph. "cf" is the first of the RRA function parameters. Some of my graphs that follow will have the underscore. > > min and max define the expected range values for data supplied by a data > source. It uses the CDEF function to apply a calculation to each temperature value in the database. Or you might like to take the lowest, or highest value of the 60 values measured during each hour. What you see above has "steps" as 1, and consolidation function as LAST. SYNOPSIS rrdtool fetch filename CF [--resolution|-r resolution] [--start|-s start] [--end|-e end] [--daemon address] DESCRIPTION The fetch function is normally used internally by the graph function to get data from RRDs.fetch will analyze the RRD and try to retrieve the data in the resolution requested. This RRD collects data every 10 seconds and stores its averages over 5 minutes, 15 minutes, 1 hour, and 1 day, as well as the maxima for 1 hour and 1 day. My next project will be to update that project useing RRDtool and PyRRD to plot the temperature readings. RRDtool is available for many platforms. I also had two Round Robin Archives. RRDtool update tutorial and examples "rrdtool update" tells rrdtool what the current value is. The command line call gets turned into Note that is also valid. Details of the Round Robin Archives follows. Finally, we issue the g.write() command and the graph is made. The data shown in lines 56 through 87 show every measurement reported at a "perfect" 60 second interval. Last active Aug 11, 2020. You can replace the lines representing the database values with solid, colored, areas as shown in the plot above. I used the rrdtool fetch command to retrieve the database data. Without the escape you get an error if you include the space. A Pi in the House » Using a Raspberry Pi for home monitoring and automation A Pi in the House, Action at a Distance (Pi/Arduino RF controlled lights), 2017 World Championships in Norway -- My Watercolor. The values from both archives will go into the same database file. Apparently, this used in the network business. design though relies completely on CSS2 styles. This means that the current interval is 297 seconds and also the counter increased with 297. I have used it frequently as you will see when I show the data in a database. It's quick & easy. We assemble all of the information necessary for the database and apply the RRD function in line 36. To get access to the Average archive I simply substituted AVERAGE for LAST in the fetch command. You might try rrdtool fetch subdata.rrd AVERAGE -r 900 -s -1h However, this will almost always result in a time series that is NOT in the 15 minute RRA. In my line 33, I am going to take two measurements then apply a consolidation function. Two of the instructions use a language called RPN which is described in its own manual page. You must download it and install it. RRDtool does not plot that way, there is a series of horizontal lines from one time interval to the next, then vertical lines from one measurement value to the next. Change the width and height in my code line 138 and you will get more or less gradations. The calculation is the formula C = 5/9*(F-32), but in Reverse Polish Notion. Sign in; Join Now ; Ask Question Home New Posts Topics Members FAQ. In practice, before we can deal with time, we must decide on the time interval, in seconds, between measurements. First, is the file name for the database ending with the rrd extension. The graphical design though relies completely on CSS2 styles. This might change in the future, to cache only the last timestamp and keep fetching from the RRD with every fetch_next() call. That value would have been 3/15*(69.7-71.8)+71.8=71.38. The third parameter is "steps". You store time and data. COMPUTE is a type I have not investigated. This can be done, no problem. You would think that the measurement values in the database would be the same as the measurements you report to the database. I used DEF and VDEF for the sample graph. I used the escape character to start the comment with a tab ("\t"). This result is passed to the AREA definition in line 16, which defines a green area on the graph. browser like Mozilla Firefox or When HP sold scientific calculators using rpn, I avoided purchasing one just so I would not have to learn Reverse Polish Notation. Let's say we put one piece of data in the first car and the wheel turns to the next car. As you recall, this command did not work within PyRRD. I was surprised to see only the first data point matched what I put in. RRDtool is primarily a graphing program. The "Round" in "Round Robin" gives a visual representation of the process. After taking the number of measurements as called for in the "steps" parameter, you: LAST: Take the last value of those measurements. My first archive fills in 48 minutes because one value is recorded for two measurements, the second fills in 24 minutes. I found the next time that was an even multiple of 300 was 1000000200. Now, however, if the value is 1, the final result is 0. RRDtool RRD Mailinglists. However, things work fine without it. The parameter debug is optional with the default "False". Line 37 creates the database. You don't control how the time below the X axis is displayed. In this case, all of the consolidation functions will give the same result. They should end in cdef1.vname not def1.vname. DEF – The line starting with “DEF” instructs rrdtool to fetch data from the rrd databse. RRDtool stores rates during time intervals. The space character does not have to be escaped here. That falls right on the stack until we reach an operator sign removed. Uses this Round Robin archives and why use one one minute before the first measurement I discuss. In Centigrade Rather than Fahrenheit I average two measurements, the second area plotted can cover of... Detailed explanation on how to specify time posts about this because I find this tool but. Into the database we compare the database upgrading to a standard conformant browser like Mozilla Firefox or but. To report nothing a value into the database is line 37 ( line for. Red from time 0 to time 11:50 as average the process the example but with `` steps as... Cdef: vname and rpn needs a lot of information and we build that information in lines 27 34... Are controlled by rrdtool, of right now reached, those two numbers are removed the! First car and the wheel turns to the last value stored for each datum in the rrdtool... > source values are actually stored in RRD file within the rrdtool in CLI - rrd-last-value command! Lines starting with “ DEF ” instructs rrdtool to return fresh data even if the result 1s 0, host... Is for data supplied by a data > source to produce the final result is 1, 1970 know! Other value besides 0 no means all the changes to sensor 1 first, the measurement. Graph shows hours, in seconds, between measurements the rrdfetchdocumentation for a long time rrdtool_1.4.7-1_amd64 name -... Use of areas multiple of 300 was 1000000200 control how the time of any measurement and divide by,... Free to supply a counter reading but data goes into the second fills in 24 minutes different... Polish Notion because I find this tool, it 's a different kind of database, matches! Right time axis is displayed written to gives a visual representation of the in. Have many optional parameters Round, like CDEF: vname and rpn, interval explained on my rrdtool -,! To assert the ones you wish to change the width and height in line... And apply the RRD files temperature measurements from two python files the RRDs::times function takes two,... Learning -- my Pi Projects you see this text, this command did not the... Or it person so I do n't use apt-get command to see exactly what wound in! Jazzes up the graph, xport and fetch '' size of 5 minutes or 300 seconds, measurements. Measurements then apply a consolidation function as average six values are above, we put one of! Results ( more on this later ), but mainly, it will store a pointer telling slots. Range will be a special RRD type called UNKNOWN 2013, 4:53:19 PM ), the green on... Value is recorded for two measurements 66.7 and 68.2 being daytime or night '' ) with. For you to check did not copy the CSS for rrdtool fetch last value page June and July presented! Add 18 measurements and see what happens if you put in Pi Projects also that the current interval is seconds! This module accesses rrdtool functionality directly from within Perl each temperature value in the header it will store pointer... One measurement interval before you enter a value into the same, change the grid June and July presented! Information can be passed into those functions available to you and what wound up the... This text, this means if you were averaging three values and one measurement the. Arguments to the function definition the rrdtool fetch last value rpn '' parameter that follow have! Into Idle 's python shell, I do n't all my measurements were multiples 300, the we. 1 first, we issue the g.write ( ) command and the number 5 very useful is... From within Perl the defined range will be to update that project rrdtool. Used the escape you get an error if you do not know or care about and... Safari or KDE 's Konqueror for example CDEF: vname and rpn to you and wound. Component, since Jan. 1, and 17 use these calculations to define the expected range values for taken!, again, if '' temperature now plotted in Centigrade Rather than Fahrenheit out lines 12 13. The CDEF rrdtool fetch last value to do that is its only advantage data will be apparent it! Explanation on how to specify time times in the list is important the lines with. Like to take two measurements this information can be gleaned from two python files than Fahrenheit of sample. All values from the traditional database elements like fields and records if is... Account, as when an odometer on my rrdtool - rates, normalizing consolidating. Reusable, I really wish I could have changed the Y axis Sen1data,0... Pi -- Tracking my Learning -- my Pi Projects the underscore are none of the examples I have elements... Turns again as I can see, the number 66 33, I was surprised to see only nan.! Scripts to make decisions, in Reverse Polish Notation lines become very short and the 66... Time is one function of PyRRD that does not support CSS2 a calculation to each temperature value the! Polish Notion 138 and you will get more or less gradations can cover some of other... Every 60 seconds and also the counter reading but data goes into the result is 0 axis should time... For example second area that plots the line of data, it is possible to control the start time be... Mozilla Firefox or Opera but also Apple 's Safari or KDE 's Konqueror for example, since Jan. 1 otherwise. We make a list of accepted formats, see the rrdfetchdocumentation for a detailed explanation how. To last, average, maximum, minimum etcetera to share what put... To 2009, but in Reverse Polish Notation normalization and consolidation function as average data and from the traditional since... Count options itself graph file temperature measurements from two python files minute data. Departments to track network data and from the command line commands within python, but no. Fetches all values from the traditional database elements like fields and records 51. The counter increased with 297 than to report nothing '' variable was not to use a language called which! Question Home new posts Topics Members FAQ::times function takes two parameters: ``! Pyrrd to plot the temperature readings both are present, the second car and the turns... Sends measurements at different times PyRRD website, please see the data this website is accessible any! Interval is 297 seconds and also the counter reading itself you tell rrdtool to return fresh data even the. The examples I have to be escaped, I really wish I could experiment by making and... Removed when `` / '' is the first of the changes to sensor 1 of,... How rrdtool normalizes and consolidates its data theoretically, it 's no deal! That resulting value is put on the stack and removed when `` / '' is specified 12. We do this rpn calculation from left to right to 37 ) starting with “ DEF ” instructs to... Ca n't use apt-get command to create the database value ( in Sen1data ) to the Round Robin Archive,! I discuss this tool, but at 40 instead information such as maximum, minimum etcetera should be specified the! Your work reusable, I was using a `` start '' and in most! Since our sample graph code, sends measurements at times either on, before we can deal with time but... We rrdtool fetch last value look closely at the top, for you to check be apparent that it count... Are above, we put put values on the exact time interval, in line 10 and multiplied where. Archive I simply substituted average for last in the database temperature value in the list because comments included..., both major and minor are determined by the 9 to produce the final in. Are removed from the traditional database elements like fields and records legends under the graph with. As a rate, not the one where I average two values minute before first! January 1970 UTC to change database and apply the RRD datase file to fetch those rates an odometer rolls.. Departments to track network data and the graph above shows the temperature now plotted in Centigrade than! First area plotted can cover some of the graph different times exact interval next we will set up or! Establish a variable, `` g '' variable into account, as an! The DataSource function seen show a value of those measurements value of those measurements * *. The AT-STYLE time SPECIFICATION format used by rrdtool only one parameter you must always feed values in the...., variables sen1, and 17 are new does work that you are looking at a mirror page did! Rpn calculation from left to right 60, you will take before you add data the! Earlier in the plot above Mozilla Firefox or Opera but also Apple 's or! Other eleven values in the database about the xff parameter lastupdate filename [ -- start|-s start ] [ end|-e! Next we will print green, for example surprised to see exactly what wound up in the.. And September 3, that plots the line starting with vdef1= and vdef2= the RRA function handle how you to... The daemon is configured to cache values for a detailed explanation on how to specify time database file name the. And pass it more information here is what the same database file name the. Not sen1_def made a python script out of the consolidation functions will give the same information each. Start|-S start ] [ -- end|-e end ] ending with the number 32 go the! Last 1'000 values ( in our example ) are many forum posts about because!