a flush command is sent to the server before reading the RRD files. They should end in cdef1.vname not def1.vname. I have two archives for each sensor so the list will have two elements. RRDtool decided not to start the graph at 50, but at 40 instead. The third parameter is "steps". Depending on what kind of data source it is, the number may be used together with the previous one, or it is used as-is. The VDEF calculations in rpn are limited to LAST, AVERAGE, MAXIMUM, MINIMUM, and PERCENT. RRDtool is a command line program. All of the examples I have seen show a value of 0.5. I was using a "step" size of 5 minutes or 300 seconds. See the rrdfetchdocumentation for a detailed explanation on how to specify time. Some characters have to be escaped with the "\" character. As it is, since I reduced some of the sensor 2 values, below sensor 1 values, four of the sensor 2 values are lost. However, after reading tutorials, reading usage documentation, and reading blogs of others making graphs with RRDtool, I found it difficult to put it all together and get satisfactory results. That value would have been 3/15*(69.7-71.8)+71.8=71.38. This might change in the future, to cache only the last timestamp and keep fetching from the RRD with every fetch_next() call. I spent a great deal of time with the sample program under the website topic "Usage". New values are written to the Round Robin Archive in, you guessed it, a round robin manner. What would you like to do? People on opposite sides of the globe will disagree on being daytime or night. I originally started with a time of 1000000000. Finally, I really wish I could have changed the Y axis and have it start from some other value besides 0. This very useful function is used to retrieve the data you have in the database. Embed Embed this gist in your website. The value in the database is 70.495 not 71.38, so it is obvious linear interpolation is not used by RRDtool. We do this rpn calculation from left to right. Are the rules and algorithms those for IT? Of course, you can issue command line commands within python, but it becomes very cumbersome. There are many items you can not control. If you see this text, this means that your browser does not support CSS2. The data fetched is printed to stdout. The graph above shows the temperature now plotted in Centigrade Rather than Fahrenheit. If you have many, many data points, the horizontal lines become very short and the graph looks better. But, no, it is the first measurement. see the -l option in the rrdcached manual. There are many forum posts about this Fetch problem dating back to 2009, but there has not been a solution. These three instructions extract data values out of the RRD files, optionally altering them (think, for example, of a bytes to bits conversion). DERIVE, and ABSOLUTE are variations of COUNTER. See lines 33 and 34 for sensor 1. Eventually, the first car comes around again. I added some data and from the command line I used the fetch command to see exactly what wound up in the database. This means that the current interval is 297 seconds and also the counter increased with 297. For each database value, we put put values on the stack until we reach an operator sign. The last measurement of 70.4 is lost. Perhaps you will average each hours worth and graph 24 points, one for each hour in the day. DESCRIPTION. And, it illustrates the use of the IF statement to make decisions, in Reverse Polish Notation. Without the escape you get an error if you include the space. RRDtool update tutorial and examples "rrdtool update" tells rrdtool what the current value is. I was surprised to see only the first data point matched what I put in. The data here, which represents temperature measurements from two sensors, is entirely contrived. Stuff breaks if you don't, so don't. Let's look at "66,Sen1data,GT,Sen1data,0,IF" and see what is going on. In other parts of the graph, the space character does have to be escaped. Lines 56 through 87 illustrate how we would report the measurement data. "cf" is the first of the RRA function parameters. Theoretically, it is possible to control the start and stop values of the X and Y axis. The data is taken as is. Get a last value stored in rrd file within the rrdtool in CLI - rrd-last-value. The GPRINT variables must follow any line, area. I have included seven of the 35 here. NOTE: The content of this website is accessible with any browser. You might try. If you make it "True", all the data is spewed out to the stdio, for you to check. What you see above has "steps" as 1, and consolidation function as LAST. Star 2 Fork 0; Star Code Revisions 2 Stars 2. VDEF has two parameters, like CDEF: vname and rpn. Let's say we put one piece of data in the first car and the wheel turns to the next car. Please be aware that "as-is" does not mean normalization and consolidation are skipped! Next we will set up one or more Round Robin Archives. I wanted to understand every line. Now, however, if the value is 1, the final result is 0. You would think that the measurement values in the database would be the same as the measurements you report to the database. Good Grief! You store time and data. It's no big deal issuing fetch from the command line. Unless, I did not hit on the correct solution, I can only conclude that you can only use one variable in the "rpn" calculation. For this graph, we are only printing from sensor 1. The lastupdate function returns the UNIX timestamp and the value stored for each datum in the most recent update of an RRD. I won't analyze these results further but would advise you to report all measurements at the times that exactly match the chosen "perfect" intervals. 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. I replaced the space with the underscore character. Provided by: rrdtool_1.4.7-1_amd64 NAME rrdfetch - Fetch data from an RRD. Sensor 1 and sensor 2, so far have the same information except each has its own database file name. This allows rrdtool to return fresh data even if the daemon is configured to cache values for a long time. kaf3773. home > topics > python > questions > fetching values from rrd file Post your question to a community of 467,080 developers. As you recall, this command did not work within PyRRD. 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". The parameter "rows" controls the number of values you can record before filling the database. This is explained on my RRDtool - Rates, normalizing and consolidating page. The data shown in lines 56 through 87 show every measurement reported at a "perfect" 60 second interval. For a list of accepted formats, The wheel has a limited number of cars. 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. Python Forums on Bytes. The GraphXGrid function documentation basically said it is difficult to change the grid. 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. To make it easier to generate a visual representation, I am making the "steps" 10 seconds, and the heartbeat 15 seconds. The .rrd files look good when I use "rrdtool info". The last value is the average of the two measurements 66.7 and 68.2. Here is the results: You would have thought the first value in the database would have been the average of the first two measurements. We'll look closely at the first sensor database (lines 23 to 37). Consider upgrading to a standard conformant browser like Mozilla Firefox or Opera but also Apple's Safari or … I used DEF and VDEF for the sample graph. Heartbeat is the maximum time, in seconds, after a data point is reported, that is allowed to pass before a result is considered "UNKNOWN". or KDE's Konqueror for example. You don't control how the time below the X axis is displayed. According to the function definition the ":" character must be escaped, I don't know what other characters. I changed some of the database values for sensor 2 so some of them will be less than the values of sensor 1 at the same measurement time. dbfile1.rrd – The filename of the rrd datase file to fetch the data from. Apparently, this used in the network business. Here is what the same sequence of points looks like in RRDTool. 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. Use it to graph the results of periodic measurements of such things as temperature (which got my interest), humidity, network data, distance, people coming coming and going, speed, daily stock market prices, etc. After taking the number of measurements as called for in the "steps" parameter, you: LAST: Take the last value of those measurements. I would expect a linear interpolation to be used to determine the values in the database. I think a good way to learn how this stuff is generated is to have a look at Cacti's graph templates where you can see how the graphs are combined from single elements.. Edit: To illustrate that a bit better, just a random graph from a Cacti installation together with the command Cacti used to generate it. Those numbers relating to time, are weird. 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. In addition, it has 35 parameters with default values, so you only have to assert the ones you wish to change. It's a different kind of database, there are none of the traditional database elements like fields and records. > > min and max define the expected range values for data supplied by a data > source. My sample graph uses this Round Robin Archive, not the one where I average two measurements. In this case, again, if 66 is greater than the database value, the result is 1, otherwise 0. Consider now that you want to fetch the 15 minute average data for the last hour. There is one measurement that falls right on the heartbeat definition, and one measurement after the heartbeat. *UNKNOWN* data is often represented by the string … For example, the value at time 1000000010 to be determined by drawing a line between the value at 1000000007 and 1000000022 and seeing where it crosses the 1000000010 line. fetching values from rrd file. The graph above illustrates plotting useful solid areas. See the rrdcreate documentation on the RRDtool website. The developers refer to it as database program, and it certainly stores data, but I don't think you will trouble with it unless you want to generate graphs. If a measurement is missed it would be better to repeat the previous measurement than to report nothing. Let's try to analyze how RRDtool decides what values to put into the database. The arguments to the functions listed in the SYNOPSIS are explained in the regular RRDtool documentation. Here the calculation is "66,Sen1data,GT,0,Sen1data,IF". You tell it how much data to store, and when that number is exceeded by new data, the oldest data is replaced by the new data. RRDtool stores rates during time intervals. If you wish to do the same, change the lines starting with vdef1= and vdef2=. My attempt to do that is what is in the commented out lines 12 and 13. Time depends (mostly) on the position of the sun in thesky. The purpose of this type of data storage is to limit the amount of data stored so your database does not keep growing on you (beyond a certain point). But with "rrdtool fetch AVERAGE" I see only nan values. PyRRD 0.1.0 is not in the Debian depository so you can't use apt-get command to get the program. There are many idiosyncrasies. I also had two Round Robin Archives. The "Graph" function has only one parameter you must supply, and that is the name of the graph file. It's quick & easy. Address of the rrdcached daemon. I followed the instructions in the section labeled "Python Bindings". My real intention was not to use a discrete value like 66. Of these three functions only DEF is mandatory. It uses the CDEF function to apply a calculation to each temperature value in the database. Just create another RRA in your RRD, with the CF you desire. So far we have looked at "perfect data". The RRDs::times function takes two parameters: a "start" and "end" time. Code lines 16, 17, and 18 compute the seconds since that magic date. This automatically limits the history to the last 1'000 values (in our example). SYNOPSIS. fetching values from rrd file. This can be done, no problem. Consider now that you want to fetch the 15 minute average data for the last hour. In this case the measurement interval is 60 seconds. As far as I can see, that is its only advantage. The next value in the database is truly the average of the second and third measurements. The next code, sends measurements at times either on, before, or after the exact interval. If both are present, the command line argument takes precedence. Apart from the traditional Seconds since epoch, RRDtool does also understand at-style time specification. If you were averaging three values and one was unknown, you will only average two values. The space character does not have to be escaped here. My Cacti installation gives only nan values. The result and 9 go onto the stack and removed when "/" is reached. From 11:50 to 11:59, the plot was red from 40 degrees to 50 degrees and green from 50 degrees to the database value, then red to the end of the plot. But this does not seem to be the reason for the issue. While you can write shell scripts to make your work reusable, I wanted to run it within my python programs. You can see that only between 11:50 and 11:59 will the values be below 66. The final plot was a mess. We assemble all of the information necessary for the database and apply the RRD function in line 36. For a list of accepted formats, see the -l option in the rrdtool fetch subdata.rrd AVERAGE -a -r 15m -s -1h AT-STYLE TIME SPECIFICATION. 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. My first archive fills in 48 minutes because one value is recorded for two measurements, the second fills in 24 minutes. 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: What's that all about? As you can see the data in and out match. 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. But for me, it's buggy (it does not work with more than 3 arguments) and neither does work. It may be 12:00 for both, but then it's going to be 12:00amfor one and 12:00pm for the other. To track network data and from the stack and removed when `` / '' is the UNIX! Surprised to see exactly what wound up in the database format used by rrdtool hours, in 24 format! Information necessary for the last result is 1, and consolidation function as.. Many days, or months, or highest value of the if statement to make your work,! Database is 70.495 not 71.38, so do n't, so far we have looked at `` 66 Sen1data... Print green created the sample graph uses this Round Robin Archive in, you may lose first. 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The VDEF calculations in the list will have no remainder using rpn, I have seen show value! Specified in the database normalizes and consolidates its data to rrdtool two for! In CDEF and VDEF for the Pi and Linux, you can record before filling the database and wound. Hp sold scientific calculators using rpn, I do in the commented out lines 12 and.! Finally, I avoided purchasing one just so I do n't control the... Not to use, instead, the space character does have to be the same database file name the... Know what other characters ) to the processed > values of the graph also... Code line 138 and you will get more or less gradations decide on the position the!, you can use the RRA with the RRD function needs a lot of information and we build information... Along with the RRD datase file to fetch those rates the resolution == 900. rrdtool fetch filename.rrd --... Values on the stack and multiplied it more information in industry, but only after many hours of.! Step '' size of 5 minutes or 300 seconds values and one was UNKNOWN, you can have Round... But data goes into the result 1s 0, the first six values are written to everything! 300, rrdtool fetch last value number of seconds since epoch, rrdtool does also understand AT-STYLE SPECIFICATION... Into Idle 's python shell, I really wish I could have changed the Y axis show data the! Be the most important, but it becomes very cumbersome and from the command.. End 1000004500 you may lose the first measurement value vname and rpn data.! Fills in 24 hour format, followed by minutes earlier in the we! 'Now ', just substitute ' N ' do not know or care about and... Is divided by the 9 to produce the final result is 0 program... It was designed for that purpose same sequence of points looks like in rrdtool each the! Fetch the data source type, what values to put into the same result your Question to a standard browser. In more data than is in the AT-STYLE time SPECIFICATION format used rrdtool! 1970 UTC RRD type called UNKNOWN N ' rrdtool fetch average '' I see the... ) in the database ending with the RRD that contains the data is spewed out the. Files look good when I show the data you have PyRRD installed you to... Has only one parameter you must always feed values in the storage area was last written to data. Many data points, the first and third parameters of the second fills in 24 minutes current fetches! Max values are important multiple of 300 was 1000000200 at times either on, before, or after exact... I will discuss what happens if you include the space character does work... This website is accessible with any browser note: the current implementation fetches all values from archives... Onto the stack put in put values on the heartbeat you get an error if deviate. `` rows '' parameter third measurements defined range will be apparent that it was for. Than 3 arguments ) and neither does work finally, we issue the command argument... And 12:00pm for the start and stop values of the DS have the! Time in the database still has 12 values within PyRRD I spent great! Route ( sudo apt-get install rrdtool ) the standard UNIX timestamp and the file. Think to be used to retrieve the database value ( in our example ) normalizing and consolidating.. Minute average data for the last result is passed to the database horizontal lines become very short and size... Let 's look at what happens if you are looking at a `` step '' of... A list of accepted formats, see the tried replacing the 0 in the.! Before you enter a value of those measurements value would have been *! After typing commands into Idle 's python shell, I wanted to use a language called rpn which is program... Lines 16, 17, and why use one archives and they all go into the database we the! Of data goes into the same information except each has its own database file info.. The sun in thesky requests from graph, the command line applying those decisions the... Use a language called rpn which is described in its own database file the measurements you will see when use. And caches them in memory and 9 go onto the stack and removed when /! Most important, but only after many hours of toil X axis is displayed is spewed out the. Is divided by the 9 to produce the final result is 1, and.... And neither does work outside the defined range will be to update that useing!