A metric can be anything that you can express as a number, for example: To create metrics inside our application we can use one of many Prometheus client libraries. We know that the more labels on a metric, the more time series it can create. This is because once we have more than 120 samples on a chunk efficiency of varbit encoding drops. *) in region drops below 4. Adding labels is very easy and all we need to do is specify their names. What happens when somebody wants to export more time series or use longer labels? Sign in AFAIK it's not possible to hide them through Grafana. what does the Query Inspector show for the query you have a problem with? Simply adding a label with two distinct values to all our metrics might double the number of time series we have to deal with. Our patched logic will then check if the sample were about to append belongs to a time series thats already stored inside TSDB or is it a new time series that needs to be created. I know prometheus has comparison operators but I wasn't able to apply them. On the worker node, run the kubeadm joining command shown in the last step. Grafana renders "no data" when instant query returns empty dataset I am interested in creating a summary of each deployment, where that summary is based on the number of alerts that are present for each deployment. Is a PhD visitor considered as a visiting scholar? PROMQL: how to add values when there is no data returned? result of a count() on a query that returns nothing should be 0 ? Are you not exposing the fail metric when there hasn't been a failure yet? The more labels you have, or the longer the names and values are, the more memory it will use. By default Prometheus will create a chunk per each two hours of wall clock. Thanks, To subscribe to this RSS feed, copy and paste this URL into your RSS reader. what error message are you getting to show that theres a problem? It will record the time it sends HTTP requests and use that later as the timestamp for all collected time series. A time series is an instance of that metric, with a unique combination of all the dimensions (labels), plus a series of timestamp & value pairs - hence the name time series. This is the last line of defense for us that avoids the risk of the Prometheus server crashing due to lack of memory. Each Prometheus is scraping a few hundred different applications, each running on a few hundred servers. This helps Prometheus query data faster since all it needs to do is first locate the memSeries instance with labels matching our query and then find the chunks responsible for time range of the query. This means that looking at how many time series an application could potentially export, and how many it actually exports, gives us two completely different numbers, which makes capacity planning a lot harder. node_cpu_seconds_total: This returns the total amount of CPU time. How do you get out of a corner when plotting yourself into a corner, Partner is not responding when their writing is needed in European project application. Lets adjust the example code to do this. This works fine when there are data points for all queries in the expression. Names and labels tell us what is being observed, while timestamp & value pairs tell us how that observable property changed over time, allowing us to plot graphs using this data. which version of Grafana are you using? This works well if errors that need to be handled are generic, for example Permission Denied: But if the error string contains some task specific information, for example the name of the file that our application didnt have access to, or a TCP connection error, then we might easily end up with high cardinality metrics this way: Once scraped all those time series will stay in memory for a minimum of one hour. Arithmetic binary operators The following binary arithmetic operators exist in Prometheus: + (addition) - (subtraction) * (multiplication) / (division) % (modulo) ^ (power/exponentiation) privacy statement. but it does not fire if both are missing because than count() returns no data the workaround is to additionally check with absent() but it's on the one hand annoying to double-check on each rule and on the other hand count should be able to "count" zero . entire corporate networks, By setting this limit on all our Prometheus servers we know that it will never scrape more time series than we have memory for. Although, sometimes the values for project_id doesn't exist, but still end up showing up as one. PromQL allows querying historical data and combining / comparing it to the current data. count() should result in 0 if no timeseries found #4982 - GitHub A metric is an observable property with some defined dimensions (labels). how have you configured the query which is causing problems? So it seems like I'm back to square one. Although, sometimes the values for project_id doesn't exist, but still end up showing up as one. This also has the benefit of allowing us to self-serve capacity management - theres no need for a team that signs off on your allocations, if CI checks are passing then we have the capacity you need for your applications. If both the nodes are running fine, you shouldnt get any result for this query. This is true both for client libraries and Prometheus server, but its more of an issue for Prometheus itself, since a single Prometheus server usually collects metrics from many applications, while an application only keeps its own metrics. How to react to a students panic attack in an oral exam? notification_sender-. Yeah, absent() is probably the way to go. This works fine when there are data points for all queries in the expression. Sign up and get Kubernetes tips delivered straight to your inbox. Selecting data from Prometheus's TSDB forms the basis of almost any useful PromQL query before . Already on GitHub? Internally time series names are just another label called __name__, so there is no practical distinction between name and labels. Is it plausible for constructed languages to be used to affect thought and control or mold people towards desired outcomes? The advantage of doing this is that memory-mapped chunks dont use memory unless TSDB needs to read them. Its very easy to keep accumulating time series in Prometheus until you run out of memory. To get a better idea of this problem lets adjust our example metric to track HTTP requests. Returns a list of label names. bay, What is the point of Thrower's Bandolier? This is because the only way to stop time series from eating memory is to prevent them from being appended to TSDB. Improving your monitoring setup by integrating Cloudflares analytics data into Prometheus and Grafana Pint is a tool we developed to validate our Prometheus alerting rules and ensure they are always working website To better handle problems with cardinality its best if we first get a better understanding of how Prometheus works and how time series consume memory. Each time series stored inside Prometheus (as a memSeries instance) consists of: The amount of memory needed for labels will depend on the number and length of these. If all the label values are controlled by your application you will be able to count the number of all possible label combinations. You must define your metrics in your application, with names and labels that will allow you to work with resulting time series easily. The most basic layer of protection that we deploy are scrape limits, which we enforce on all configured scrapes. The process of sending HTTP requests from Prometheus to our application is called scraping. Prometheus's query language supports basic logical and arithmetic operators. This is what i can see on Query Inspector. If you do that, the line will eventually be redrawn, many times over. The number of times some specific event occurred. Is there a single-word adjective for "having exceptionally strong moral principles"? We know what a metric, a sample and a time series is. The next layer of protection is checks that run in CI (Continuous Integration) when someone makes a pull request to add new or modify existing scrape configuration for their application. Well occasionally send you account related emails. Can airtags be tracked from an iMac desktop, with no iPhone? metric name, as measured over the last 5 minutes: Assuming that the http_requests_total time series all have the labels job and can help you on Its least efficient when it scrapes a time series just once and never again - doing so comes with a significant memory usage overhead when compared to the amount of information stored using that memory. We know that time series will stay in memory for a while, even if they were scraped only once. So there would be a chunk for: 00:00 - 01:59, 02:00 - 03:59, 04:00 - 05:59, , 22:00 - 23:59. The below posts may be helpful for you to learn more about Kubernetes and our company. accelerate any Even i am facing the same issue Please help me on this. Thats why what our application exports isnt really metrics or time series - its samples. Find centralized, trusted content and collaborate around the technologies you use most. It will return 0 if the metric expression does not return anything. That map uses labels hashes as keys and a structure called memSeries as values. Have a question about this project? Other Prometheus components include a data model that stores the metrics, client libraries for instrumenting code, and PromQL for querying the metrics. By clicking Sign up for GitHub, you agree to our terms of service and All regular expressions in Prometheus use RE2 syntax. Instead we count time series as we append them to TSDB. We can add more metrics if we like and they will all appear in the HTTP response to the metrics endpoint. This page will guide you through how to install and connect Prometheus and Grafana. Is a PhD visitor considered as a visiting scholar? It would be easier if we could do this in the original query though. I am always registering the metric as defined (in the Go client library) by prometheus.MustRegister(). That way even the most inexperienced engineers can start exporting metrics without constantly wondering Will this cause an incident?. Making statements based on opinion; back them up with references or personal experience. Use it to get a rough idea of how much memory is used per time series and dont assume its that exact number. Both of the representations below are different ways of exporting the same time series: Since everything is a label Prometheus can simply hash all labels using sha256 or any other algorithm to come up with a single ID that is unique for each time series. This is the modified flow with our patch: By running go_memstats_alloc_bytes / prometheus_tsdb_head_series query we know how much memory we need per single time series (on average), we also know how much physical memory we have available for Prometheus on each server, which means that we can easily calculate the rough number of time series we can store inside Prometheus, taking into account the fact the theres garbage collection overhead since Prometheus is written in Go: memory available to Prometheus / bytes per time series = our capacity. It doesnt get easier than that, until you actually try to do it. After a few hours of Prometheus running and scraping metrics we will likely have more than one chunk on our time series: Since all these chunks are stored in memory Prometheus will try to reduce memory usage by writing them to disk and memory-mapping. PROMQL: how to add values when there is no data returned? Is it possible to rotate a window 90 degrees if it has the same length and width? Ive added a data source(prometheus) in Grafana. job and handler labels: Return a whole range of time (in this case 5 minutes up to the query time) from and what youve done will help people to understand your problem. By merging multiple blocks together, big portions of that index can be reused, allowing Prometheus to store more data using the same amount of storage space. You can verify this by running the kubectl get nodes command on the master node. And then there is Grafana, which comes with a lot of built-in dashboards for Kubernetes monitoring. Going back to our time series - at this point Prometheus either creates a new memSeries instance or uses already existing memSeries. Making statements based on opinion; back them up with references or personal experience. If you look at the HTTP response of our example metric youll see that none of the returned entries have timestamps. Stumbled onto this post for something else unrelated, just was +1-ing this :). I made the changes per the recommendation (as I understood it) and defined separate success and fail metrics. By clicking Sign up for GitHub, you agree to our terms of service and By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. To set up Prometheus to monitor app metrics: Download and install Prometheus. One of the first problems youre likely to hear about when you start running your own Prometheus instances is cardinality, with the most dramatic cases of this problem being referred to as cardinality explosion. Are there tables of wastage rates for different fruit and veg? Although you can tweak some of Prometheus' behavior and tweak it more for use with short lived time series, by passing one of the hidden flags, its generally discouraged to do so. Finally getting back to this. Will this approach record 0 durations on every success? So lets start by looking at what cardinality means from Prometheus' perspective, when it can be a problem and some of the ways to deal with it. Blocks will eventually be compacted, which means that Prometheus will take multiple blocks and merge them together to form a single block that covers a bigger time range. Asking for help, clarification, or responding to other answers. This doesnt capture all complexities of Prometheus but gives us a rough estimate of how many time series we can expect to have capacity for. There is no equivalent functionality in a standard build of Prometheus, if any scrape produces some samples they will be appended to time series inside TSDB, creating new time series if needed. Hello, I'm new at Grafan and Prometheus. This allows Prometheus to scrape and store thousands of samples per second, our biggest instances are appending 550k samples per second, while also allowing us to query all the metrics simultaneously. following for every instance: we could get the top 3 CPU users grouped by application (app) and process Thank you for subscribing! Operators | Prometheus Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. Minimising the environmental effects of my dyson brain. In addition to that in most cases we dont see all possible label values at the same time, its usually a small subset of all possible combinations. whether someone is able to help out. Is that correct? Are there tables of wastage rates for different fruit and veg? This helps us avoid a situation where applications are exporting thousands of times series that arent really needed. *) in region drops below 4. alert also has to fire if there are no (0) containers that match the pattern in region. If we let Prometheus consume more memory than it can physically use then it will crash. You saw how PromQL basic expressions can return important metrics, which can be further processed with operators and functions. Knowing that it can quickly check if there are any time series already stored inside TSDB that have the same hashed value. @juliusv Thanks for clarifying that. without any dimensional information. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. But you cant keep everything in memory forever, even with memory-mapping parts of data. Neither of these solutions seem to retain the other dimensional information, they simply produce a scaler 0. promql - Prometheus query check if value exist - Stack Overflow What sort of strategies would a medieval military use against a fantasy giant? Now we should pause to make an important distinction between metrics and time series. Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, How Intuit democratizes AI development across teams through reusability. Not the answer you're looking for? For example our errors_total metric, which we used in example before, might not be present at all until we start seeing some errors, and even then it might be just one or two errors that will be recorded. About an argument in Famine, Affluence and Morality. You can calculate how much memory is needed for your time series by running this query on your Prometheus server: Note that your Prometheus server must be configured to scrape itself for this to work. In Prometheus pulling data is done via PromQL queries and in this article we guide the reader through 11 examples that can be used for Kubernetes specifically. The result is a table of failure reason and its count. Internally all time series are stored inside a map on a structure called Head. which Operating System (and version) are you running it under? There are a number of options you can set in your scrape configuration block. How is Jesus " " (Luke 1:32 NAS28) different from a prophet (, Luke 1:76 NAS28)? PromQL queries the time series data and returns all elements that match the metric name, along with their values for a particular point in time (when the query runs). What can a lawyer do if the client wants him to be acquitted of everything despite serious evidence? Operating such a large Prometheus deployment doesnt come without challenges. Note that using subqueries unnecessarily is unwise. Prometheus metrics can have extra dimensions in form of labels. Is there a solutiuon to add special characters from software and how to do it. t]. These flags are only exposed for testing and might have a negative impact on other parts of Prometheus server. Play with bool This is the standard Prometheus flow for a scrape that has the sample_limit option set: The entire scrape either succeeds or fails. I have a query that gets a pipeline builds and its divided by the number of change request open in a 1 month window, which gives a percentage. How to tell which packages are held back due to phased updates. to your account, What did you do? Asking for help, clarification, or responding to other answers. In general, having more labels on your metrics allows you to gain more insight, and so the more complicated the application you're trying to monitor, the more need for extra labels. While the sample_limit patch stops individual scrapes from using too much Prometheus capacity, which could lead to creating too many time series in total and exhausting total Prometheus capacity (enforced by the first patch), which would in turn affect all other scrapes since some new time series would have to be ignored. Lets say we have an application which we want to instrument, which means add some observable properties in the form of metrics that Prometheus can read from our application. So I still can't use that metric in calculations ( e.g., success / (success + fail) ) as those calculations will return no datapoints. To learn more about our mission to help build a better Internet, start here. If you're looking for a I'm not sure what you mean by exposing a metric. Basically our labels hash is used as a primary key inside TSDB. The Head Chunk is never memory-mapped, its always stored in memory. attacks, keep By default Prometheus will create a chunk per each two hours of wall clock. Have you fixed this issue? Can I tell police to wait and call a lawyer when served with a search warrant? Variable of the type Query allows you to query Prometheus for a list of metrics, labels, or label values. information which you think might be helpful for someone else to understand For example, I'm using the metric to record durations for quantile reporting. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. but viewed in the tabular ("Console") view of the expression browser. Samples are compressed using encoding that works best if there are continuous updates. VictoriaMetrics handles rate () function in the common sense way I described earlier! count(container_last_seen{environment="prod",name="notification_sender.*",roles=".application-server."}) I suggest you experiment more with the queries as you learn, and build a library of queries you can use for future projects. Youll be executing all these queries in the Prometheus expression browser, so lets get started. Is it a bug? I'm displaying Prometheus query on a Grafana table. Cardinality is the number of unique combinations of all labels. Find centralized, trusted content and collaborate around the technologies you use most. Passing sample_limit is the ultimate protection from high cardinality. This helps Prometheus query data faster since all it needs to do is first locate the memSeries instance with labels matching our query and then find the chunks responsible for time range of the query. The problem is that the table is also showing reasons that happened 0 times in the time frame and I don't want to display them. The main reason why we prefer graceful degradation is that we want our engineers to be able to deploy applications and their metrics with confidence without being subject matter experts in Prometheus. Examples Your needs or your customers' needs will evolve over time and so you cant just draw a line on how many bytes or cpu cycles it can consume. Each time series will cost us resources since it needs to be kept in memory, so the more time series we have, the more resources metrics will consume. The subquery for the deriv function uses the default resolution. TSDB used in Prometheus is a special kind of database that was highly optimized for a very specific workload: This means that Prometheus is most efficient when continuously scraping the same time series over and over again. Using a query that returns "no data points found" in an expression. Better to simply ask under the single best category you think fits and see So, specifically in response to your question: I am facing the same issue - please explain how you configured your data So there would be a chunk for: 00:00 - 01:59, 02:00 - 03:59, 04:00 . Prometheus is an open-source monitoring and alerting software that can collect metrics from different infrastructure and applications. Querying examples | Prometheus count(container_last_seen{name="container_that_doesn't_exist"}), What did you see instead? To get a better understanding of the impact of a short lived time series on memory usage lets take a look at another example. @zerthimon You might want to use 'bool' with your comparator positions. Or maybe we want to know if it was a cold drink or a hot one? Now, lets install Kubernetes on the master node using kubeadm. One thing you could do though to ensure at least the existence of failure series for the same series which have had successes, you could just reference the failure metric in the same code path without actually incrementing it, like so: That way, the counter for that label value will get created and initialized to 0. Of course, this article is not a primer on PromQL; you can browse through the PromQL documentation for more in-depth knowledge. Theres only one chunk that we can append to, its called the Head Chunk. I'm still out of ideas here. I cant see how absent() may help me here @juliusv yeah, I tried count_scalar() but I can't use aggregation with it. We can use these to add more information to our metrics so that we can better understand whats going on. Secondly this calculation is based on all memory used by Prometheus, not only time series data, so its just an approximation. Prometheus - exclude 0 values from query result, How Intuit democratizes AI development across teams through reusability. The way labels are stored internally by Prometheus also matters, but thats something the user has no control over. 1 Like. The actual amount of physical memory needed by Prometheus will usually be higher as a result, since it will include unused (garbage) memory that needs to be freed by Go runtime. Under which circumstances? The main motivation seems to be that dealing with partially scraped metrics is difficult and youre better off treating failed scrapes as incidents. Looking to learn more? Thirdly Prometheus is written in Golang which is a language with garbage collection. it works perfectly if one is missing as count() then returns 1 and the rule fires. Inside the Prometheus configuration file we define a scrape config that tells Prometheus where to send the HTTP request, how often and, optionally, to apply extra processing to both requests and responses. Prometheus is an open-source monitoring and alerting software that can collect metrics from different infrastructure and applications. This might require Prometheus to create a new chunk if needed.
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