prometheus query return 0 if no data

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. Prometheus Authors 2014-2023 | Documentation Distributed under CC-BY-4.0. I can't work out how to add the alerts to the deployments whilst retaining the deployments for which there were no alerts returned: If I use sum with or, then I get this, depending on the order of the arguments to or: If I reverse the order of the parameters to or, I get what I am after: But I'm stuck now if I want to do something like apply a weight to alerts of a different severity level, e.g. 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. 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. He has a Bachelor of Technology in Computer Science & Engineering from SRMS. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. Play with bool The real power of Prometheus comes into the picture when you utilize the alert manager to send notifications when a certain metric breaches a threshold. Return all time series with the metric http_requests_total: Return all time series with the metric http_requests_total and the given It will return 0 if the metric expression does not return anything. We had a fair share of problems with overloaded Prometheus instances in the past and developed a number of tools that help us deal with them, including custom patches. I'm displaying Prometheus query on a Grafana table. *) in region drops below 4. alert also has to fire if there are no (0) containers that match the pattern in region. which version of Grafana are you using? 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. 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. 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. This is because the Prometheus server itself is responsible for timestamps. Monitoring our monitoring: how we validate our Prometheus alert rules 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. what error message are you getting to show that theres a problem? Hello, I'm new at Grafan and Prometheus. How do I align things in the following tabular environment? To get a better idea of this problem lets adjust our example metric to track HTTP requests. 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. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. Since the default Prometheus scrape interval is one minute it would take two hours to reach 120 samples. 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. Prometheus lets you query data in two different modes: The Console tab allows you to evaluate a query expression at the current time. Before that, Vinayak worked as a Senior Systems Engineer at Singapore Airlines. I'd expect to have also: Please use the prometheus-users mailing list for questions. Prometheus query check if value exist. 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. privacy statement. Prometheus is an open-source monitoring and alerting software that can collect metrics from different infrastructure and applications. So the maximum number of time series we can end up creating is four (2*2). Why is this sentence from The Great Gatsby grammatical? 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. Is there a solutiuon to add special characters from software and how to do it. Select the query and do + 0. It's worth to add that if using Grafana you should set 'Connect null values' proeprty to 'always' in order to get rid of blank spaces in the graph. Then imported a dashboard from " 1 Node Exporter for Prometheus Dashboard EN 20201010 | Grafana Labs ".Below is my Dashboard which is showing empty results.So kindly check and suggest. Operating such a large Prometheus deployment doesnt come without challenges. your journey to Zero Trust. Are there tables of wastage rates for different fruit and veg? Once TSDB knows if it has to insert new time series or update existing ones it can start the real work. Prometheus's query language supports basic logical and arithmetic operators. what error message are you getting to show that theres a problem? Returns a list of label names. With 1,000 random requests we would end up with 1,000 time series in Prometheus. group by returns a value of 1, so we subtract 1 to get 0 for each deployment and I now wish to add to this the number of alerts that are applicable to each deployment. The difference with standard Prometheus starts when a new sample is about to be appended, but TSDB already stores the maximum number of time series its allowed to have. We know what a metric, a sample and a time series is. So when TSDB is asked to append a new sample by any scrape, it will first check how many time series are already present. That's the query ( Counter metric): sum (increase (check_fail {app="monitor"} [20m])) by (reason) The result is a table of failure reason and its count. @zerthimon The following expr works for me A common pattern is to export software versions as a build_info metric, Prometheus itself does this too: When Prometheus 2.43.0 is released this metric would be exported as: Which means that a time series with version=2.42.0 label would no longer receive any new samples. Is it suspicious or odd to stand by the gate of a GA airport watching the planes? Can I tell police to wait and call a lawyer when served with a search warrant? 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. This gives us confidence that we wont overload any Prometheus server after applying changes. No, only calling Observe() on a Summary or Histogram metric will add any observations (and only calling Inc() on a counter metric will increment it). Run the following commands in both nodes to configure the Kubernetes repository. Well be executing kubectl commands on the master node only. Making statements based on opinion; back them up with references or personal experience. which Operating System (and version) are you running it under? Its very easy to keep accumulating time series in Prometheus until you run out of memory. Comparing current data with historical data. Both rules will produce new metrics named after the value of the record field. The more labels you have and the more values each label can take, the more unique combinations you can create and the higher the cardinality. Explanation: Prometheus uses label matching in expressions. which outputs 0 for an empty input vector, but that outputs a scalar The Graph tab allows you to graph a query expression over a specified range of time. Why do many companies reject expired SSL certificates as bugs in bug bounties? Timestamps here can be explicit or implicit. 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. We protect Secondly this calculation is based on all memory used by Prometheus, not only time series data, so its just an approximation. Its also worth mentioning that without our TSDB total limit patch we could keep adding new scrapes to Prometheus and that alone could lead to exhausting all available capacity, even if each scrape had sample_limit set and scraped fewer time series than this limit allows. For a list of trademarks of The Linux Foundation, please see our Trademark Usage page. 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. How can i turn no data to zero in Loki - Grafana Loki - Grafana Labs Please dont post the same question under multiple topics / subjects. Any excess samples (after reaching sample_limit) will only be appended if they belong to time series that are already stored inside TSDB. Next you will likely need to create recording and/or alerting rules to make use of your time series. Using regular expressions, you could select time series only for jobs whose Well occasionally send you account related emails. By default Prometheus will create a chunk per each two hours of wall clock. When you add dimensionality (via labels to a metric), you either have to pre-initialize all the possible label combinations, which is not always possible, or live with missing metrics (then your PromQL computations become more cumbersome). or Internet application, Already on GitHub? By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. If we try to visualize how the perfect type of data Prometheus was designed for looks like well end up with this: A few continuous lines describing some observed properties. All regular expressions in Prometheus use RE2 syntax. Prometheus metrics can have extra dimensions in form of labels. Finally getting back to this. But before that, lets talk about the main components of Prometheus. metric name, as measured over the last 5 minutes: Assuming that the http_requests_total time series all have the labels job Will this approach record 0 durations on every success? Now comes the fun stuff. This is the last line of defense for us that avoids the risk of the Prometheus server crashing due to lack of memory. Connect and share knowledge within a single location that is structured and easy to search. Having better insight into Prometheus internals allows us to maintain a fast and reliable observability platform without too much red tape, and the tooling weve developed around it, some of which is open sourced, helps our engineers avoid most common pitfalls and deploy with confidence. The Linux Foundation has registered trademarks and uses trademarks. Internet-scale applications efficiently, Making statements based on opinion; back them up with references or personal experience. The result is a table of failure reason and its count. It saves these metrics as time-series data, which is used to create visualizations and alerts for IT teams. How to tell which packages are held back due to phased updates. We can use these to add more information to our metrics so that we can better understand whats going on. an EC2 regions with application servers running docker containers. We can add more metrics if we like and they will all appear in the HTTP response to the metrics endpoint. Im new at Grafan and Prometheus. Once Prometheus has a list of samples collected from our application it will save it into TSDB - Time Series DataBase - the database in which Prometheus keeps all the time series. So just calling WithLabelValues() should make a metric appear, but only at its initial value (0 for normal counters and histogram bucket counters, NaN for summary quantiles). In reality though this is as simple as trying to ensure your application doesnt use too many resources, like CPU or memory - you can achieve this by simply allocating less memory and doing fewer computations. To set up Prometheus to monitor app metrics: Download and install Prometheus. for the same vector, making it a range vector: Note that an expression resulting in a range vector cannot be graphed directly, Run the following commands on the master node, only copy the kubeconfig and set up Flannel CNI. Using a query that returns "no data points found" in an - GitHub Querying basics | Prometheus To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Once the last chunk for this time series is written into a block and removed from the memSeries instance we have no chunks left. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. I used a Grafana transformation which seems to work. Asking for help, clarification, or responding to other answers. Yeah, absent() is probably the way to go. At the moment of writing this post we run 916 Prometheus instances with a total of around 4.9 billion time series. Combined thats a lot of different metrics. Managed Service for Prometheus Cloud Monitoring Prometheus # ! For Prometheus to collect this metric we need our application to run an HTTP server and expose our metrics there. If the total number of stored time series is below the configured limit then we append the sample as usual. So perhaps the behavior I'm running into applies to any metric with a label, whereas a metric without any labels would behave as @brian-brazil indicated? There's also count_scalar(), bay, A metric is an observable property with some defined dimensions (labels). Lets adjust the example code to do this. If such a stack trace ended up as a label value it would take a lot more memory than other time series, potentially even megabytes. Does a summoned creature play immediately after being summoned by a ready action? This would inflate Prometheus memory usage, which can cause Prometheus server to crash, if it uses all available physical memory. Find centralized, trusted content and collaborate around the technologies you use most. I'm displaying Prometheus query on a Grafana table. Why are trials on "Law & Order" in the New York Supreme Court? PROMQL: how to add values when there is no data returned? You can use these queries in the expression browser, Prometheus HTTP API, or visualization tools like Grafana. what does the Query Inspector show for the query you have a problem with? 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). To select all HTTP status codes except 4xx ones, you could run: Return the 5-minute rate of the http_requests_total metric for the past 30 minutes, with a resolution of 1 minute. Selecting data from Prometheus's TSDB forms the basis of almost any useful PromQL query before . Now, lets install Kubernetes on the master node using kubeadm. 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. You can query Prometheus metrics directly with its own query language: PromQL. I believe it's the logic that it's written, but is there any conditions that can be used if there's no data recieved it returns a 0. what I tried doing is putting a condition or an absent function,but not sure if thats the correct approach. This scenario is often described as cardinality explosion - some metric suddenly adds a huge number of distinct label values, creates a huge number of time series, causes Prometheus to run out of memory and you lose all observability as a result.

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