prometheus query return 0 if no data

Add field from calculation Binary operation. But the real risk is when you create metrics with label values coming from the outside world. How to tell which packages are held back due to phased updates. Neither of these solutions seem to retain the other dimensional information, they simply produce a scaler 0. Which in turn will double the memory usage of our Prometheus server. Other Prometheus components include a data model that stores the metrics, client libraries for instrumenting code, and PromQL for querying the metrics. On the worker node, run the kubeadm joining command shown in the last step. Asking for help, clarification, or responding to other answers. Run the following command on the master node: Once the command runs successfully, youll see joining instructions to add the worker node to the cluster. Better to simply ask under the single best category you think fits and see I'm displaying Prometheus query on a Grafana table. 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. without any dimensional information. There is an open pull request on the Prometheus repository. to your account. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Prometheus provides a functional query language called PromQL (Prometheus Query Language) that lets the user select and aggregate time series data in real time. It doesnt get easier than that, until you actually try to do it. Once TSDB knows if it has to insert new time series or update existing ones it can start the real work. With any monitoring system its important that youre able to pull out the right data. Those limits are there to catch accidents and also to make sure that if any application is exporting a high number of time series (more than 200) the team responsible for it knows about it. Thanks, Each chunk represents a series of samples for a specific time range. Yeah, absent() is probably the way to go. This single sample (data point) will create a time series instance that will stay in memory for over two and a half hours using resources, just so that we have a single timestamp & value pair. However when one of the expressions returns no data points found the result of the entire expression is no data points found.In my case there haven't been any failures so rio_dashorigin_serve_manifest_duration_millis_count{Success="Failed"} returns no data points found.Is there a way to write the query so that a . Please dont post the same question under multiple topics / subjects. it works perfectly if one is missing as count() then returns 1 and the rule fires. This is the last line of defense for us that avoids the risk of the Prometheus server crashing due to lack of memory. A time series that was only scraped once is guaranteed to live in Prometheus for one to three hours, depending on the exact time of that scrape. Can airtags be tracked from an iMac desktop, with no iPhone? Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. For example, if someone wants to modify sample_limit, lets say by changing existing limit of 500 to 2,000, for a scrape with 10 targets, thats an increase of 1,500 per target, with 10 targets thats 10*1,500=15,000 extra time series that might be scraped. will get matched and propagated to the output. I was then able to perform a final sum by over the resulting series to reduce the results down to a single result, dropping the ad-hoc labels in the process. 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. gabrigrec September 8, 2021, 8:12am #8. bay, When time series disappear from applications and are no longer scraped they still stay in memory until all chunks are written to disk and garbage collection removes them. the problem you have. If you look at the HTTP response of our example metric youll see that none of the returned entries have timestamps. This is in contrast to a metric without any dimensions, which always gets exposed as exactly one present series and is initialized to 0. The nature of simulating nature: A Q&A with IBM Quantum researcher Dr. Jamie We've added a "Necessary cookies only" option to the cookie consent popup. I believe it's the logic that it's written, but is there any . To this end, I set up the query to instant so that the very last data point is returned but, when the query does not return a value - say because the server is down and/or no scraping took place - the stat panel produces no data. Prometheus allows us to measure health & performance over time and, if theres anything wrong with any service, let our team know before it becomes a problem. We covered some of the most basic pitfalls in our previous blog post on Prometheus - Monitoring our monitoring. We know what a metric, a sample and a time series is. In the screenshot below, you can see that I added two queries, A and B, but only . If instead of beverages we tracked the number of HTTP requests to a web server, and we used the request path as one of the label values, then anyone making a huge number of random requests could force our application to create a huge number of time series. The reason why we still allow appends for some samples even after were above sample_limit is that appending samples to existing time series is cheap, its just adding an extra timestamp & value pair. To make things more complicated you may also hear about samples when reading Prometheus documentation. If so it seems like this will skew the results of the query (e.g., quantiles). Has 90% of ice around Antarctica disappeared in less than a decade? https://github.com/notifications/unsubscribe-auth/AAg1mPXncyVis81Rx1mIWiXRDe0E1Dpcks5rIXe6gaJpZM4LOTeb. There will be traps and room for mistakes at all stages of this process. Even i am facing the same issue Please help me on this. Second rule does the same but only sums time series with status labels equal to "500". Just add offset to the query. The main motivation seems to be that dealing with partially scraped metrics is difficult and youre better off treating failed scrapes as incidents. This process helps to reduce disk usage since each block has an index taking a good chunk of disk space. 02:00 - create a new chunk for 02:00 - 03:59 time range, 04:00 - create a new chunk for 04:00 - 05:59 time range, 22:00 - create a new chunk for 22:00 - 23:59 time range. 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. The below posts may be helpful for you to learn more about Kubernetes and our company. but viewed in the tabular ("Console") view of the expression browser. count the number of running instances per application like this: This documentation is open-source. instance_memory_usage_bytes: This shows the current memory used. Return the per-second rate for all time series with the http_requests_total Looking at memory usage of such Prometheus server we would see this pattern repeating over time: The important information here is that short lived time series are expensive. You can verify this by running the kubectl get nodes command on the master node. Find centralized, trusted content and collaborate around the technologies you use most. Lets see what happens if we start our application at 00:25, allow Prometheus to scrape it once while it exports: And then immediately after the first scrape we upgrade our application to a new version: At 00:25 Prometheus will create our memSeries, but we will have to wait until Prometheus writes a block that contains data for 00:00-01:59 and runs garbage collection before that memSeries is removed from memory, which will happen at 03:00. - grafana-7.1.0-beta2.windows-amd64, how did you install it? 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. Connect and share knowledge within a single location that is structured and easy to search. Thirdly Prometheus is written in Golang which is a language with garbage collection. Chunks that are a few hours old are written to disk and removed from memory. The text was updated successfully, but these errors were encountered: This is correct. 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 . Heres a screenshot that shows exact numbers: Thats an average of around 5 million time series per instance, but in reality we have a mixture of very tiny and very large instances, with the biggest instances storing around 30 million time series each. The way labels are stored internally by Prometheus also matters, but thats something the user has no control over. 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. Have you fixed this issue? Staging Ground Beta 1 Recap, and Reviewers needed for Beta 2, Prometheus promQL query is not showing 0 when metric data does not exists, PromQL - how to get an interval between result values, PromQL delta for each elment in values array, Trigger alerts according to the environment in alertmanger, Prometheus alertmanager includes resolved alerts in a new alert. To avoid this its in general best to never accept label values from untrusted sources. The containers are named with a specific pattern: notification_checker [0-9] notification_sender [0-9] I need an alert when the number of container of the same pattern (eg. I'm not sure what you mean by exposing a metric. Arithmetic binary operators The following binary arithmetic operators exist in Prometheus: + (addition) - (subtraction) * (multiplication) / (division) % (modulo) ^ (power/exponentiation) What video game is Charlie playing in Poker Face S01E07? There is a maximum of 120 samples each chunk can hold. 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. Use it to get a rough idea of how much memory is used per time series and dont assume its that exact number. There's also count_scalar(), I know prometheus has comparison operators but I wasn't able to apply them. In AWS, create two t2.medium instances running CentOS. Finally we maintain a set of internal documentation pages that try to guide engineers through the process of scraping and working with metrics, with a lot of information thats specific to our environment. It might seem simple on the surface, after all you just need to stop yourself from creating too many metrics, adding too many labels or setting label values from untrusted sources. The struct definition for memSeries is fairly big, but all we really need to know is that it has a copy of all the time series labels and chunks that hold all the samples (timestamp & value pairs). our free app that makes your Internet faster and safer. notification_sender-. 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. Short story taking place on a toroidal planet or moon involving flying, How to handle a hobby that makes income in US, Doubling the cube, field extensions and minimal polynoms, Follow Up: struct sockaddr storage initialization by network format-string. 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. We protect Redoing the align environment with a specific formatting. Simple, clear and working - thanks a lot. Object, url:api/datasources/proxy/2/api/v1/query_range?query=wmi_logical_disk_free_bytes%7Binstance%3D~%22%22%2C%20volume%20!~%22HarddiskVolume.%2B%22%7D&start=1593750660&end=1593761460&step=20&timeout=60s, Powered by Discourse, best viewed with JavaScript enabled, 1 Node Exporter for Prometheus Dashboard EN 20201010 | Grafana Labs, https://grafana.com/grafana/dashboards/2129. Please help improve it by filing issues or pull requests. Using a query that returns "no data points found" in an expression. Every two hours Prometheus will persist chunks from memory onto the disk. We can use these to add more information to our metrics so that we can better understand whats going on. Samples are compressed using encoding that works best if there are continuous updates. A simple request for the count (e.g., rio_dashorigin_memsql_request_fail_duration_millis_count) returns no datapoints). You set up a Kubernetes cluster, installed Prometheus on it ,and ran some queries to check the clusters health. source, what your query is, what the query inspector shows, and any other The Graph tab allows you to graph a query expression over a specified range of time. Prometheus's query language supports basic logical and arithmetic operators. Our metrics are exposed as a HTTP response. Sign in Are there tables of wastage rates for different fruit and veg? We will examine their use cases, the reasoning behind them, and some implementation details you should be aware of. The simplest way of doing this is by using functionality provided with client_python itself - see documentation here. If the error message youre getting (in a log file or on screen) can be quoted By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. For a list of trademarks of The Linux Foundation, please see our Trademark Usage page. Please open a new issue for related bugs. In this blog post well cover some of the issues one might encounter when trying to collect many millions of time series per Prometheus instance. 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. In order to make this possible, it's necessary to tell Prometheus explicitly to not trying to match any labels by . (fanout by job name) and instance (fanout by instance of the job), we might After a chunk was written into a block and removed from memSeries we might end up with an instance of memSeries that has no chunks. Well be executing kubectl commands on the master node only. I'd expect to have also: Please use the prometheus-users mailing list for questions. prometheus promql Share Follow edited Nov 12, 2020 at 12:27 I'm still out of ideas here. The result is a table of failure reason and its count. But the key to tackling high cardinality was better understanding how Prometheus works and what kind of usage patterns will be problematic. No error message, it is just not showing the data while using the JSON file from that website. website But before that, lets talk about the main components of Prometheus. What can a lawyer do if the client wants him to be acquitted of everything despite serious evidence? So the maximum number of time series we can end up creating is four (2*2). The text was updated successfully, but these errors were encountered: It's recommended not to expose data in this way, partially for this reason. How to follow the signal when reading the schematic? What happens when somebody wants to export more time series or use longer labels? He has a Bachelor of Technology in Computer Science & Engineering from SRMS. Lets create a demo Kubernetes cluster and set up Prometheus to monitor it. I can get the deployments in the dev, uat, and prod environments using this query: So we can see that tenant 1 has 2 deployments in 2 different environments, whereas the other 2 have only one. Is there a single-word adjective for "having exceptionally strong moral principles"? The more labels you have, or the longer the names and values are, the more memory it will use. Finally we do, by default, set sample_limit to 200 - so each application can export up to 200 time series without any action. Internally all time series are stored inside a map on a structure called Head. If we were to continuously scrape a lot of time series that only exist for a very brief period then we would be slowly accumulating a lot of memSeries in memory until the next garbage collection. Time series scraped from applications are kept in memory. This helps us avoid a situation where applications are exporting thousands of times series that arent really needed. VictoriaMetrics handles rate () function in the common sense way I described earlier! This selector is just a metric name. The Prometheus data source plugin provides the following functions you can use in the Query input field. 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. If you need to obtain raw samples, then a range query must be sent to /api/v1/query. Going back to our metric with error labels we could imagine a scenario where some operation returns a huge error message, or even stack trace with hundreds of lines. The thing with a metric vector (a metric which has dimensions) is that only the series for it actually get exposed on /metrics which have been explicitly initialized.

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