There is a maximum of 120 samples each chunk can hold. This means that our memSeries still consumes some memory (mostly labels) but doesnt really do anything. Operators | Prometheus Are you not exposing the fail metric when there hasn't been a failure yet? Operating such a large Prometheus deployment doesnt come without challenges. For instance, the following query would return week-old data for all the time series with node_network_receive_bytes_total name: node_network_receive_bytes_total offset 7d We know that time series will stay in memory for a while, even if they were scraped only once. Our CI would check that all Prometheus servers have spare capacity for at least 15,000 time series before the pull request is allowed to be merged. Asking for help, clarification, or responding to other answers. What can a lawyer do if the client wants him to be acquitted of everything despite serious evidence? Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. Labels are stored once per each memSeries instance. Other Prometheus components include a data model that stores the metrics, client libraries for instrumenting code, and PromQL for querying the metrics. To avoid this its in general best to never accept label values from untrusted sources. which outputs 0 for an empty input vector, but that outputs a scalar Prometheus query check if value exist. Making statements based on opinion; back them up with references or personal experience. 11 Queries | Kubernetes Metric Data with PromQL, wide variety of applications, infrastructure, APIs, databases, and other sources. It will return 0 if the metric expression does not return anything. Since we know that the more labels we have the more time series we end up with, you can see when this can become a problem. How can i turn no data to zero in Loki - Grafana Loki - Grafana Labs Run the following commands on the master node, only copy the kubeconfig and set up Flannel CNI. In our example we have two labels, content and temperature, and both of them can have two different values. 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. This would happen if any time series was no longer being exposed by any application and therefore there was no scrape that would try to append more samples to it. We use Prometheus to gain insight into all the different pieces of hardware and software that make up our global network. @zerthimon The following expr works for me Well be executing kubectl commands on the master node only. This pod wont be able to run because we dont have a node that has the label disktype: ssd. To your second question regarding whether I have some other label on it, the answer is yes I do. To get a better understanding of the impact of a short lived time series on memory usage lets take a look at another example. 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. 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. To learn more, see our tips on writing great answers. With this simple code Prometheus client library will create a single metric. Especially when dealing with big applications maintained in part by multiple different teams, each exporting some metrics from their part of the stack. 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. 1 Like. Note that using subqueries unnecessarily is unwise. Simply adding a label with two distinct values to all our metrics might double the number of time series we have to deal with. instance_memory_usage_bytes: This shows the current memory used. node_cpu_seconds_total: This returns the total amount of CPU time. Are there tables of wastage rates for different fruit and veg? This makes a bit more sense with your explanation. So there would be a chunk for: 00:00 - 01:59, 02:00 - 03:59, 04:00 . Not the answer you're looking for? *) in region drops below 4. alert also has to fire if there are no (0) containers that match the pattern in region. If a sample lacks any explicit timestamp then it means that the sample represents the most recent value - its the current value of a given time series, and the timestamp is simply the time you make your observation at. 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. We know that each time series will be kept in memory. scheduler exposing these metrics about the instances it runs): The same expression, but summed by application, could be written like this: If the same fictional cluster scheduler exposed CPU usage metrics like the Time series scraped from applications are kept in memory. For that lets follow all the steps in the life of a time series inside Prometheus. 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. After running the query, a table will show the current value of each result time series (one table row per output series). 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. rev2023.3.3.43278. See this article for details. 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. So the maximum number of time series we can end up creating is four (2*2). 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. Arithmetic binary operators The following binary arithmetic operators exist in Prometheus: + (addition) - (subtraction) * (multiplication) / (division) % (modulo) ^ (power/exponentiation) Will this approach record 0 durations on every success? Sign up for a free GitHub account to open an issue and contact its maintainers and the community. Thirdly Prometheus is written in Golang which is a language with garbage collection. Finally we do, by default, set sample_limit to 200 - so each application can export up to 200 time series without any action. Does Counterspell prevent from any further spells being cast on a given turn? This process is also aligned with the wall clock but shifted by one hour. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. In the screenshot below, you can see that I added two queries, A and B, but only . The more any application does for you, the more useful it is, the more resources it might need. 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. But before doing that it needs to first check which of the samples belong to the time series that are already present inside TSDB and which are for completely new time series. There's also count_scalar(), Prometheus provides a functional query language called PromQL (Prometheus Query Language) that lets the user select and aggregate time series data in real time. The TSDB limit patch protects the entire Prometheus from being overloaded by too many time series. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. I suggest you experiment more with the queries as you learn, and build a library of queries you can use for future projects. 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? Grafana renders "no data" when instant query returns empty dataset windows. If, on the other hand, we want to visualize the type of data that Prometheus is the least efficient when dealing with, well end up with this instead: Here we have single data points, each for a different property that we measure. Looking to learn more? Now we should pause to make an important distinction between metrics and time series. 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. - grafana-7.1.0-beta2.windows-amd64, how did you install it? These are the sane defaults that 99% of application exporting metrics would never exceed. The result of an expression can either be shown as a graph, viewed as tabular data in Prometheus's expression browser, or consumed by external systems via the HTTP API. PromQL allows querying historical data and combining / comparing it to the current data. Is a PhD visitor considered as a visiting scholar? First is the patch that allows us to enforce a limit on the total number of time series TSDB can store at any time. Staging Ground Beta 1 Recap, and Reviewers needed for Beta 2, Show or hide query result depending on variable value in Grafana, Understanding the CPU Busy Prometheus query, Group Label value prefixes by Delimiter in Prometheus, Why time duration needs double dot for Prometheus but not for Victoria metrics, Using a Grafana Histogram with Prometheus Buckets. 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. The subquery for the deriv function uses the default resolution. 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. 2023 The Linux Foundation. If both the nodes are running fine, you shouldnt get any result for this query. With our custom patch we dont care how many samples are in a scrape. 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. 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. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. vishnur5217 May 31, 2020, 3:44am 1. Find centralized, trusted content and collaborate around the technologies you use most. Finally you will want to create a dashboard to visualize all your metrics and be able to spot trends. 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. Here is the extract of the relevant options from Prometheus documentation: Setting all the label length related limits allows you to avoid a situation where extremely long label names or values end up taking too much memory. Having good internal documentation that covers all of the basics specific for our environment and most common tasks is very important. You can run a variety of PromQL queries to pull interesting and actionable metrics from your Kubernetes cluster. A metric is an observable property with some defined dimensions (labels). He has a Bachelor of Technology in Computer Science & Engineering from SRMS. You set up a Kubernetes cluster, installed Prometheus on it ,and ran some queries to check the clusters health. 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. In this article, you will learn some useful PromQL queries to monitor the performance of Kubernetes-based systems. 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. Today, let's look a bit closer at the two ways of selecting data in PromQL: instant vector selectors and range vector selectors. Has 90% of ice around Antarctica disappeared in less than a decade? Querying examples | Prometheus The only exception are memory-mapped chunks which are offloaded to disk, but will be read into memory if needed by queries. Basically our labels hash is used as a primary key inside TSDB. You can query Prometheus metrics directly with its own query language: PromQL. Asking for help, clarification, or responding to other answers. What does remote read means in Prometheus? Is it a bug? 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. Managing the entire lifecycle of a metric from an engineering perspective is a complex process. This is because the Prometheus server itself is responsible for timestamps. How to show that an expression of a finite type must be one of the finitely many possible values? 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. bay, ward off DDoS Timestamps here can be explicit or implicit. To get a better idea of this problem lets adjust our example metric to track HTTP requests. The text was updated successfully, but these errors were encountered: It's recommended not to expose data in this way, partially for this reason. Prometheus Queries: 11 PromQL Examples and Tutorial - ContainIQ