---
title: Data model
sort_rank: 1
---

# Data model

Prometheus fundamentally stores all data as [_time
series_](http://en.wikipedia.org/wiki/Time_series): streams of timestamped
values belonging to the same metric and the same set of labeled dimensions.
Besides stored time series, Prometheus may generate temporary derived time series
as the result of queries.

## Metric names and labels

Every time series is uniquely identified by its _metric name_ and a set of
_key-value pairs_, also known as _labels_.

The _metric name_ specifies the general feature of a system that is measured
(e.g. `http_requests_total` - the total number of HTTP requests received). It
may contain ASCII letters and digits, as well as underscores and colons. It
must match the regex `[a-zA-Z_:][a-zA-Z0-9_:]*`.

Labels enable Prometheus's dimensional data model: any given combination of
labels for the same metric name identifies a particular dimensional
instantiation of that metric (for example: all HTTP requests that used the
method `POST` to the `/api/tracks` handler). The query language
allows filtering and aggregation based on these dimensions. Changing any label
value, including adding or removing a label, will create a new time series.

Label names may contain ASCII letters, numbers, as well as underscores. They
must match the regex `[a-zA-Z_][a-zA-Z0-9_]*`. Label names beginning with `__`
are reserved for internal use.

Label values may contain any Unicode characters.

See also the [best practices for naming metrics and labels](/docs/practices/naming/).

## Samples
Samples form the actual time series data. Each sample consists of:

   * a float64 value
   * a millisecond-precision timestamp

## Notation
Given a metric name and a set of labels, time series are frequently identified
using this notation:

    <metric name>{<label name>=<label value>, ...}

For example, a time series with the metric name `api_http_requests_total` and
the labels `method="POST"` and `handler="/messages"` could be written like
this:

    api_http_requests_total{method="POST", handler="/messages"}

This is the same notation that [OpenTSDB](http://opentsdb.net/) uses.
