In this article, you will learn some useful PromQL queries to monitor the performance of Kubernetes-based systems. what does the Query Inspector show for the query you have a problem with? To your second question regarding whether I have some other label on it, the answer is yes I do. First rule will tell Prometheus to calculate per second rate of all requests and sum it across all instances of our server. 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. Sign in 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. If the time series doesnt exist yet and our append would create it (a new memSeries instance would be created) then we skip this sample. The main motivation seems to be that dealing with partially scraped metrics is difficult and youre better off treating failed scrapes as incidents. 4 Managed Service for Prometheus | 4 Managed Service for node_cpu_seconds_total: This returns the total amount of CPU time. Of course, this article is not a primer on PromQL; you can browse through the PromQL documentation for more in-depth knowledge. We can add more metrics if we like and they will all appear in the HTTP response to the metrics endpoint. Every two hours Prometheus will persist chunks from memory onto the disk. The second patch modifies how Prometheus handles sample_limit - with our patch instead of failing the entire scrape it simply ignores excess time series. Sign up for a free GitHub account to open an issue and contact its maintainers and the community. returns the unused memory in MiB for every instance (on a fictional cluster The more labels we have or the more distinct values they can have the more time series as a result. Each chunk represents a series of samples for a specific time range. Use it to get a rough idea of how much memory is used per time series and dont assume its that exact number. What sort of strategies would a medieval military use against a fantasy giant? 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. Simply adding a label with two distinct values to all our metrics might double the number of time series we have to deal with. If all the label values are controlled by your application you will be able to count the number of all possible label combinations. Once we appended sample_limit number of samples we start to be selective. With 1,000 random requests we would end up with 1,000 time series in Prometheus. In my case there haven't been any failures so rio_dashorigin_serve_manifest_duration_millis_count{Success="Failed"} returns no data points found. There will be traps and room for mistakes at all stages of this process. This is an example of a nested subquery. t]. 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. If we let Prometheus consume more memory than it can physically use then it will crash. But before that, lets talk about the main components of Prometheus. Which in turn will double the memory usage of our Prometheus server. You can query Prometheus metrics directly with its own query language: PromQL. For that reason we do tolerate some percentage of short lived time series even if they are not a perfect fit for Prometheus and cost us more memory. There is an open pull request on the Prometheus repository. I made the changes per the recommendation (as I understood it) and defined separate success and fail metrics. Our HTTP response will now show more entries: As we can see we have an entry for each unique combination of labels. new career direction, check out our open AFAIK it's not possible to hide them through Grafana. Chunks will consume more memory as they slowly fill with more samples, after each scrape, and so the memory usage here will follow a cycle - we start with low memory usage when the first sample is appended, then memory usage slowly goes up until a new chunk is created and we start again. This is the last line of defense for us that avoids the risk of the Prometheus server crashing due to lack of memory. The only exception are memory-mapped chunks which are offloaded to disk, but will be read into memory if needed by queries. Prometheus and PromQL (Prometheus Query Language) are conceptually very simple, but this means that all the complexity is hidden in the interactions between different elements of the whole metrics pipeline. Do roots of these polynomials approach the negative of the Euler-Mascheroni constant? Select the query and do + 0. Using a query that returns "no data points found" in an expression. To get rid of such time series Prometheus will run head garbage collection (remember that Head is the structure holding all memSeries) right after writing a block. 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. 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. what does the Query Inspector show for the query you have a problem with? Monitor Confluence with Prometheus and Grafana | Confluence Data Center Asking for help, clarification, or responding to other answers. 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. This is what i can see on Query Inspector. One of the most important layers of protection is a set of patches we maintain on top of Prometheus. but still preserve the job dimension: If we have two different metrics with the same dimensional labels, we can apply Connect and share knowledge within a single location that is structured and easy to search. The number of times some specific event occurred. 11 Queries | Kubernetes Metric Data with PromQL, wide variety of applications, infrastructure, APIs, databases, and other sources. 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. (fanout by job name) and instance (fanout by instance of the job), we might In AWS, create two t2.medium instances running CentOS. 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. Use Prometheus to monitor app performance metrics. That way even the most inexperienced engineers can start exporting metrics without constantly wondering Will this cause an incident?. Can I tell police to wait and call a lawyer when served with a search warrant? which Operating System (and version) are you running it under? Simple, clear and working - thanks a lot. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. The process of sending HTTP requests from Prometheus to our application is called scraping. Why are trials on "Law & Order" in the New York Supreme Court? Also the link to the mailing list doesn't work for me. Is what you did above (failures.WithLabelValues) an example of "exposing"? Next you will likely need to create recording and/or alerting rules to make use of your time series. instance_memory_usage_bytes: This shows the current memory used. You can use these queries in the expression browser, Prometheus HTTP API, or visualization tools like Grafana. 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. 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 article covered a lot of ground. All they have to do is set it explicitly in their scrape configuration. A common class of mistakes is to have an error label on your metrics and pass raw error objects as values. are going to make it So the maximum number of time series we can end up creating is four (2*2). 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. Cardinality is the number of unique combinations of all labels. result of a count() on a query that returns nothing should be 0 ? Here at Labyrinth Labs, we put great emphasis on monitoring. Going back to our time series - at this point Prometheus either creates a new memSeries instance or uses already existing memSeries. If you need to obtain raw samples, then a range query must be sent to /api/v1/query. Also, providing a reasonable amount of information about where youre starting 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. Prometheus will keep each block on disk for the configured retention period. Neither of these solutions seem to retain the other dimensional information, they simply produce a scaler 0. Is that correct? 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. We protect What this means is that using Prometheus defaults each memSeries should have a single chunk with 120 samples on it for every two hours of data. I then hide the original query. Before that, Vinayak worked as a Senior Systems Engineer at Singapore Airlines. your journey to Zero Trust. 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. Already on GitHub? But I'm stuck now if I want to do something like apply a weight to alerts of a different severity level, e.g. Extra metrics exported by Prometheus itself tell us if any scrape is exceeding the limit and if that happens we alert the team responsible for it. It will record the time it sends HTTP requests and use that later as the timestamp for all collected time series. 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 . About an argument in Famine, Affluence and Morality. 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. If we try to append a sample with a timestamp higher than the maximum allowed time for current Head Chunk, then TSDB will create a new Head Chunk and calculate a new maximum time for it based on the rate of appends. Redoing the align environment with a specific formatting. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, Simple succinct answer. This is because the only way to stop time series from eating memory is to prevent them from being appended to TSDB. Internally all time series are stored inside a map on a structure called Head. @zerthimon The following expr works for me This helps us avoid a situation where applications are exporting thousands of times series that arent really needed. What happens when somebody wants to export more time series or use longer labels? This works fine when there are data points for all queries in the expression. It enables us to enforce a hard limit on the number of time series we can scrape from each application instance. The number of time series depends purely on the number of labels and the number of all possible values these labels can take. rev2023.3.3.43278. Finally, please remember that some people read these postings as an email Windows 10, how have you configured the query which is causing problems? Examples We will also signal back to the scrape logic that some samples were skipped. You can verify this by running the kubectl get nodes command on the master node. Before running this query, create a Pod with the following specification: If this query returns a positive value, then the cluster has overcommitted the CPU. There is a single time series for each unique combination of metrics labels. 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. by (geo_region) < bool 4 To learn more, see our tips on writing great answers. These queries are a good starting point. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Lets pick client_python for simplicity, but the same concepts will apply regardless of the language you use. prometheus - Promql: Is it possible to get total count in Query_Range If you look at the HTTP response of our example metric youll see that none of the returned entries have timestamps. It doesnt get easier than that, until you actually try to do it. Add field from calculation Binary operation. as text instead of as an image, more people will be able to read it and help. This selector is just a metric name. 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. Staging Ground Beta 1 Recap, and Reviewers needed for Beta 2. count the number of running instances per application like this: This documentation is open-source. I cant see how absent() may help me here @juliusv yeah, I tried count_scalar() but I can't use aggregation with it. Prometheus - exclude 0 values from query result - Stack Overflow
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