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Understanding Metric Formats and Models Like OTel, Prometheus, and StatsD

Learning Objectives

• Understand what a metric is, its components, and its significance in the context of telemetry data and IT/software applications.
• Become familiar with the role metrics play in providing insights into a system's performance, behavior, and status.

• Learn about models like OpenTelemetry, Prometheus, and StatsD and their unique features.

• Recognize the importance of consistent metrics and tools like Mezmo for normalization.

Metrics are a bedrock of observability. They offer crucial insights into the performance and health of systems and applications. They are invaluable to various roles, including Site Reliability Engineers (SREs), DevOps Engineers, System Administrators, Data Analysts, Product Managers, and CTOs. Business leaders also depend on the insights derived from these metrics to help decision-making. Understanding the structure, identifying the most suitable format, and applying appropriate normalization techniques give metrics the power to inform problem resolution and decision-making. Mastering metrics can also help identify trends for businesses aiming to stay ahead.

In this piece, we delve into the anatomy of these metrics, comparing the prevalent data models – OpenTelemetry (OTel), Prometheus (Prom), and StatsD – and providing concrete examples. We’ll also explore the crucial role of telemetry pipelines in metric normalization and standardization, where they aid in transforming diverse metric data into a unified format, facilitating more efficient data management and analysis. 

Throughout this piece, we'll examine how tools like Mezmo are practical examples of implementing these strategies, highlighting the real-world benefits of mastering telemetry metrics.

What Is a Metric?

In the context of telemetry data and IT and software applications, a metric is a quantifiable measure providing valuable insights into a system's performance, status, or behavior. These measurable values, captured and monitored over regular intervals, span a wide range of aspects - from system performance (CPU usage, memory usage) and application behavior (transaction rates, error counts) to user activity (number of active users, session duration).

Consider the number of users currently logged into a web application; tracking this over time gives a metric. When collected, analyzed, and understood, these metrics reveal essential patterns, facilitate troubleshooting, and empower decision-making. Their role is indispensable for IT professionals, SREs, DevOps engineers, and data analysts, as they provide a crucial lens through which these professionals can identify potential issues, understand system usage, and guide their strategies and actions.

The Components of a Metric

At its core, a metric consists of multiple components, each playing an essential role in conveying information and ensuring clarity. 

Let’s explore the anatomy of a metric: 

  • Name: The metric’s identifier, which communicates its purpose.
  • Value: The core quantitative measure can be a single number or a set of metrics like histograms.
  • Timestamp: Marks when the metric value is captured, vital for tracking temporal changes
  • Tags / Labels: Key-value pairs that provide extra context. For instance, tags such as ‘server:server1’ pinpoint specifics.
  • Type: Indicates the metric category, distinguishing between types like counters and gauges. 
  • Unit: The standard of measurement, ensuring users interpret metrics like percentages or milliseconds correctly. 
  • Description: Also referred to as ‘metadata’. It’s a brief note offering extra clarity or context about the metric’s use or origin
  • Aggregation: How the metric has been condensed or summed up, such as through averaging. 

Understanding the anatomy of a metric equips professionals to extract meaningful insights, ensure data integrity, and make informed decisions. Each component plays a part in painting a clearer picture of system and application behavior. 

Common Metric Types and Formats

Metrics can be represented in various types and formats, each serving a unique purpose and providing distinct insights.

Common Metric Visualization Methods

  • Counter: A simple tally of an event or action, such as the number of clicks on a web page. For example, 'user_logins: 350' signifies 350 users have logged into an application.
  • Note that OpenTelemetry uses a Sum instead of a counter
  • Gauge: A snapshot of a value at a particular point in time, like the current CPU usage of a server. For instance, 'current_cpu_usage: 55%' implies that the CPU is currently operating at 55% of its capacity.
  • Histogram: Distribution of numerical data, for instance, the distribution of page load times for a website. An example would be 'load_time: {100ms: 50, 200ms: 30, 300ms: 20}', showing that 50 pages loaded in 100ms, 30 in 200ms, and 20 in 300ms.

Metric Formats

  • Ratio: Ratio is the quantitative relation between two values, showing the number of times one value contains or is contained within the other. For example, 'cache_hits_to_misses: 5:1' indicates five cache hits for every cache miss.
  • Percentage: Percentage expresses a number or ratio as a fraction of 100. For example, 'disk_usage: 75%' means 75% of the disk capacity is used.
  • Average: Average is the sum of values divided by the number of values. For instance, 'average_response_time: 200ms' signifies the mean response time is 200 milliseconds.
  • Median: Median represents the middle value in a series of numbers. For example, 'median_load_time: 150ms' means the central value of all the load times is 150 milliseconds.
  • Mode: Mode is the value appearing most frequently in a data set. An example could be 'mode_load_time: 120ms', indicating that the most common load time is 120 milliseconds.
  • Range: The range represents the difference between the highest and lowest values. For instance, 'temperature_range: 20-30°C' indicates that the temperature varies from 20 to 30 degrees Celsius.

Now that we understand the basic forms metrics come in, let’s look at the significance of data models that house and organize these metrics.

From Metrics to Models: Understanding OTel, Prom, and StatsD

Within telemetry, a data model defines the structure of data - specifically how metrics are represented, related, and stored. Choosing a data model significantly impacts how efficiently you can analyze and utilize data. The most prevalent data models in the observability and telemetry landscape are OpenTelemetry (OTel), Prometheus (Prom), and StatsD. Each of these models has unique strengths and use cases, and understanding their differences can guide the selection of the right tool for the right job.

OpenTelemetry (OTel)

OpenTelemetry provides a robust and versatile data model. It supports various metric types and allows for a rich context by correlating metrics, traces, and logs. This model excels in environments where it is crucial to connect metric data with specific traces or logs.

For example, a metric in the OTel model might look like this: otel.cpu_utilization{"serviceA","abcd1234"} 0.9. 

This metric indicates a CPU utilization of 90% for service instance "abcd1234" of "serviceA".

Prometheus (Prom)

Prometheus emphasizes a time-series based data model, storing all data as timestamped values alongside key-value pair labels. This model excels in capturing the state of the system at various points in time, making it well-suited for analyzing trends over time.

A Prometheus metric might look like this: 

prom.http_requests_total{method="POST", handler="/api/books"} 1027

Here, the metric represents a total of 1027 HTTP POST requests handled by "/api/books".


StatsD focuses on simplicity and speed. It supports basic metric types and sends metrics over UDP for minimal overhead, making it excellent for situations where high-speed and high-volume data collection is paramount.

A StatsD metric could look like this: 


This metric indicates a count (signified by 'c') of a single page view event.

OTel Sums Versus Time Series Counters

OpenTelemetry (OTel) and time series databases such as Prometheus have distinct ways of representing metrics, particularly when it comes to counters. Diving into the nuances between OTel sums and time series counters can help telemetry professionals make informed decisions when choosing between or integrating these systems.

OTel Sums

In the OTel data model, a 'sum' is a type of metric that captures the total sum of a particular measurement over a specified period. It can be both monotonic (only increasing) or non-monotonic (can decrease or increase).

Sums are particularly useful when the focus is on the cumulative value of a particular measurement. For instance, the total revenue accumulated by an application or the total number of user sign-ups.

Here are the characteristics of OTel Sums:

  • Monotonic Sums: Ideal for situations where the value can only increase. For example, the total number of users registered cannot decrease.
  • Non-monotonic Sums: Useful when the value can decrease, such as a count of items in a cart where users can add or remove items.

Time Series Counters (as in Prometheus)

In time series databases like Prometheus, a counter is a metric type that only goes up (or resets to zero). It's typically used to count the number of times an event occurs or the cumulative total of a quantity.

Time series counters are optimal for situations where you want to track increments over time. This could be anything from the number of page views, system errors, or API requests.

Key characteristics of Time Series Counters include:

  • Continuous Tracking: Time series counters provide a continuous record, capturing the state of the counter at every interval.
  • Resetting: If a counter resets (due to system restart or other reasons), it starts from zero. Systems like Prometheus can handle these resets and still compute rate over time accurately.

Comparison and Considerations:

  • Granularity: While OTel sums give you the total accumulated value over a period, time series counters provide a granular, continuous track of increments.
  • System Overheads: Continuous tracking with time series counters can lead to more system overhead due to the frequent data points. In contrast, OTel sums can be more efficient as they provide cumulative data.
  • Flexibility: OTel's non-monotonic sums offer flexibility in situations where values can decrease, whereas traditional time series counters are primarily for increasing values.

When integrating OTel with platforms like Prometheus, understanding the difference between OTel sums and time series counters becomes essential. Especially if conversions are required, ensuring data integrity and accurate representations across systems.

Further Differences

There are several other distinguishing factors among these data models:

  • Protocol and Transport: StatsD uses a UDP-based protocol which allows for fire-and-forget data sending with very low overhead. On the other hand, both OTel and Prom use HTTP/HTTPS protocols, which ensure reliable delivery but come with higher overhead.
  • Push vs. Pull Metrics: Prometheus uses a pull model where it scrapes metrics from instrumented jobs. Both StatsD and OTel use a push model, pushing metrics to the monitoring system as they occur.
  • Metric Types: StatsD supports simpler metric types such as count, timer, gauge, and set. Prometheus expands upon these types with additional ones like histograms and summaries. OTel provides the most extensive metric types supporting all that StatsD and Prom have and adding more sophisticated types like UpDownCounter, ValueObserver, and ValueRecorder.
  • Contextual Information: OTel allows correlation of metrics, logs, and traces, providing a holistic view of the system. This ability is less emphasized in StatsD and Prometheus, which focus more on metric data.
  • Integration and Instrumentation: All three models have wide community support and offer numerous client libraries in various languages. However, the ease of instrumentation can vary.
  • Storage and Visualization: Prometheus comes with its time-series database and Grafana integration for visualization. OTel and StatsD are more flexible and do not prescribe any specific storage or visualization solution, allowing you to choose what best fits your needs.

The choice between OTel, Prom, and StatsD is crucial. It's not about just housing metrics, but shaping your telemetry data landscape. Each model carries unique capabilities affecting your data's organization, analysis, and overall observability. In essence, the right data model not only stores but significantly standardizes and influences your telemetry data.

Telemetry Pipelines and Metrics

Telemetry pipelines play a pivotal role in the world of metrics, acting as the backbone for metric normalization. They ensure that metric data, regardless of its source or initial format, can be transformed and presented in a standardized way. Additionally, they support aggregation to reduce granularity and manage costs. Here’s why they’re crucial:

  • Unified Analysis: With a consistent data format, professionals can run analyses without having to constantly adjust to different metric structures. This ensures quicker, more efficient evaluations and comparisons, even when the data is sourced from diverse systems.
  • Integration Flexibility: A standardized metric format provides greater flexibility when integrating with various tools and platforms. Whether it's visualization tools, storage databases, or monitoring solutions, a unified format reduces compatibility issues.
  • Optimized Storage: By ensuring that metrics are normalized, telemetry pipelines can help optimize data storage. Instead of housing multiple variants of the same metric, streamlined data means reduced redundancy and better utilization of storage resources.
  • Enhanced Alerting: Consistency in metrics ensures that alert thresholds and triggers can be set up with greater accuracy. This prevents false positives and ensures that teams are alerted to genuine issues in real-time.
  • Effective Aggregation: By aggregating metrics, telemetry pipelines reduce data granularity. This isn’t just about compressing data but also deriving insights from large datasets without incurring excessive costs or compromising clarity. 

By facilitating efficient data management and analysis, telemetry pipelines don't just normalize data; they elevate the metric monitoring process, ensuring data-driven decisions are based on quality, consistent information.

The Importance of Normalizing Metrics

Normalization ensures that metrics are consistent and interpretable.

Mezmo helps tackle challenges like inconsistent data formats and ensures metrics are stored, actionable, and ready for insightful analyses. Mezmo specializes in converting metrics from their source format and automatically transitioning them to an external format using our specific metric data model. The true value of this normalization is that it provides a seamless method for users to ingest OTel metrics directly into platforms like Prometheus.

However, it's important to note that changes are on the horizon. The impending native support for OTel metrics in Prometheus, as outlined in this article, signifies that while normalization remains valuable, its significance might be poised for a shift. It's crucial for organizations not just to adapt but anticipate. While normalization is a linchpin, its evolving dynamics underscore the need for continuous learning and adaptation.

Nevertheless, with Mezmo, users can aggregate metrics while normalizing, ensuring they don't have to rely solely on platforms like Prometheus.

Moreover, maintaining limited tag cardinality still offers undeniable value despite these changes.

Metrics Mastery: Strategic Advantage In Telemetry 

Metrics are a technical necessity and a strategic advantage for observability. By understanding, comparing, and efficiently managing them, organizations secure invaluable insights and position themselves for informed decision-making, optimized operations, and sustainable growth while staying future-proofed against an evolving telemetry landscape.

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