--- title: InfluxDB data elements description: > InfluxDB structures data using elements such as timestamps, field keys, field values, tags, etc. weight: 102 menu: influxdb_2_0_ref: parent: Key concepts name: Data elements influxdb/v2.0/tags: [key concepts, schema] --- InfluxDB 2.0 includes the following data elements: - [timestamp](#timestamp) - [field key](#field-key) - [field value](#field-value) - [field set](#field-set) - [tag key](#tag-key) - [tag value](#tag-value) - [tag set](#tag-set) - [measurement](#measurement) - [series](#series) - [point](#point) - [bucket](#bucket) - [bucket schema](#bucket-schema) - [organization](#organization) The sample data below is used to illustrate data elements concepts. _Hover over highlighted terms to get acquainted with InfluxDB terminology and layout._ **bucket:** `my_bucket` | _time | _measurement | {{< tooltip "Tag key" "location" >}} | {{< tooltip "Tag key" "scientist" >}} | _field | _value | |:------------------- |:------------ |:------- |:------ |:-- |:------ | | 2019-08-18T00:00:00Z | census | klamath | anderson | bees | 23 | | 2019-08-18T00:00:00Z | census | portland | mullen | ants | 30 | | 2019-08-18T00:06:00Z | census | klamath | anderson | bees | 28 | | {{< tooltip "Timestamp" "2019-08-18T00:06:00Z" >}} | {{< tooltip "measurement" "census" >}} | {{< tooltip "Tag value" "portland" >}} | {{< tooltip "Tag value" "mullen">}} | {{< tooltip "Field key" "ants" >}} | {{< tooltip "Field value" "32" >}} | ## Timestamp All data stored in InfluxDB has a `_time` column that stores timestamps. On disk, timestamps are stored in epoch nanosecond format. InfluxDB formats timestamps show the date and time in [RFC3339](/influxdb/v2.0/reference/glossary/#rfc3339-timestamp) UTC associated with data. Timestamp precision is important when you write data. ## Measurement The `_measurement` column shows the name of the measurement `census`. Measurement names are strings. A measurement acts as a container for tags, fields, and timestamps. Use a measurement name that describes your data. The name `census` tells us that the field values record the number of `bees` and `ants`. ## Fields A field includes a field key stored in the `_field` column and a field value stored in the `_value` column. ### Field key A field key is a string that represents the name of the field. In the sample data above, `bees` and `ants` are field keys. ### Field value A field value represents the value of an associated field. Field values can be strings, floats, integers, or booleans. The field values in the sample data show the number of `bees` at specified times: `23`, and `28` and the number of `ants` at a specified time: `30` and `32`. ### Field set A field set is a collection of field key-value pairs associated with a timestamp. The sample data includes the following field sets: ```bash census bees=23i,ants=30i 1566086400000000000 census bees=28i,ants=32i 1566086760000000000 ----------------- Field set ``` {{% note %}} **Fields aren't indexed:** Fields are required in InfluxDB data and are not indexed. Queries that filter field values must scan all field values to match query conditions. As a result, queries on tags > are more performant than queries on fields. **Store commonly queried metadata in tags.** {{% /note %}} ## Tags The columns in the sample data, `location` and `scientist`, are tags. Tags include tag keys and tag values that are stored as strings and metadata. ### Tag key The tag keys in the sample data are `location` and `scientist`. _For information about tag key requirements, see [Line protocol – Tag set](/influxdb/v2.0/reference/syntax/line-protocol/#tag-set)._ ### Tag value The tag key `location` has two tag values: `klamath` and `portland`. The tag key `scientist` also has two tag values: `anderson` and `mullen`. _For information about tag value requirements, see [Line protocol – Tag set](/influxdb/v2.0/reference/syntax/line-protocol/#tag-set)._ ### Tag set The collection of tag key-value pairs make up a tag set. The sample data includes the following four tag sets: ```bash location = klamath, scientist = anderson location = portland, scientist = anderson location = klamath, scientist = mullen location = portland, scientist = mullen ``` {{% note %}} **Tags are indexed:** Tags are optional. You don't need tags in your data structure, but it's typically a good idea to include tags. Because tags are indexed, queries on tags are faster than queries on fields. This makes tags ideal for storing commonly-queried metadata. {{% /note %}} {{% note %}} Tags containing highly variable information like UUIDs, hashes, and random strings will lead to a large number of unique series in the database, known as **high series cardinality**. High series cardinality is a primary driver of high memory usage for many database workloads. See [series cardinality](/influxdb/v2.0/reference/glossary/#series-cardinality) for more information. {{% /note %}} #### Why your schema matters If most of your queries focus on values in the fields, for example, a query to find when 23 bees were counted: ```js from(bucket: "bucket-name") |> range(start: 2019-08-17T00:00:00Z, stop: 2019-08-19T00:00:00Z) |> filter(fn: (r) => r._field == "bees" and r._value == 23) ``` InfluxDB scans every field value in the dataset for `bees` before the query returns a response. If our sample `census` data grew to millions of rows, to optimize your query, you could rearrange your [schema](/influxdb/v2.0/reference/glossary/#schema) so the fields (`bees` and `ants`) becomes tags and the tags (`location` and `scientist`) become fields: | _time | _measurement | {{< tooltip "Tag key" "bees" >}} | _field | _value | |:------------------- |:------------ |:------- |:-- |:------ | | 2019-08-18T00:00:00Z | census | 23 | location | klamath | | 2019-08-18T00:00:00Z | census | 23 | scientist | anderson | | 2019-08-18T00:06:00Z | census | {{< tooltip "Tag value" "28" >}} | {{< tooltip "Field key" "location" >}} | {{< tooltip "Field value" "klamath" >}} | | 2019-08-18T00:06:00Z | census | 28 | scientist | anderson | | _time | _measurement | {{< tooltip "Tag key" "ants" >}} | _field | _value | |:------------------- |:------------ |:------- |:-- |:------ | | 2019-08-18T00:00:00Z | census | 30 | location | portland | | 2019-08-18T00:00:00Z | census | 30 | scientist | mullen | | 2019-08-18T00:06:00Z | census | {{< tooltip "Tag value" "32" >}} | {{< tooltip "Field key" "location" >}} | {{< tooltip "Field value" "portland" >}} | | 2019-08-18T00:06:00Z | census | 32 | scientist | mullen | Now that `bees` and `ants` are tags, InfluxDB doesn't have to scan all `_field` and `_value` columns. This makes your queries faster. ## Bucket schema In InfluxDB Cloud, a bucket with the `explicit` schema-type requires an explicit schema for each measurement. Measurements contain tags, fields, and timestamps. An explicit schema constrains the shape of data that can be written to that measurement. The following schema constrains `census` data: name | type | data_type |:------- |:---------------|:-------------------- time | timestamp | location | tag | string scientist | tag | string ants | field | integer bees | field | integer ## Series Now that you're familiar with measurements, field sets, and tag sets, it's time to discuss series keys and series. A **series key** is a collection of points that share a measurement, tag set, and field key. For example, the [sample data](#sample-data) includes two unique series keys: | _measurement | tag set | _field | |:------------- |:------------------------------- |:------ | | census | {{< tooltip "Tag set" "location=klamath,scientist=anderson" >}} | {{< tooltip "Field key" "bees" >}} | | census | location=portland,scientist=mullen | ants | A **series** includes timestamps and field values for a given series key. From the sample data, here's a **series key** and the corresponding **series**: ```bash # series key census,location=klamath,scientist=anderson bees # series 2019-08-18T00:00:00Z 23 2019-08-18T00:06:00Z 28 ``` Understanding the concept of a series is essential when designing your [schema](/influxdb/v2.0/reference/glossary/#schema) and working with your data in InfluxDB. ## Point A **point** includes the series key, a field value, and a timestamp. For example, a single point from the [sample data](#sample-data) looks like this: `2019-08-18T00:00:00Z census ants 30 portland mullen` ## Bucket All InfluxDB data is stored in a bucket. A **bucket** combines the concept of a database and a retention period (the duration of time that each data point persists). A bucket belongs to an organization. For more information about buckets, see [Manage buckets](/influxdb/v2.0/organizations/buckets/). ## Organization An InfluxDB **organization** is a workspace for a group of [users](/influxdb/v2.0/users/). All [dashboards](/influxdb/v2.0/visualize-data/dashboards/), [tasks](/influxdb/v2.0/process-data/), buckets, and users belong to an organization. For more information about organizations, see [Manage organizations](/influxdb/v2.0/organizations/). If you're just starting out, we recommend taking a look at the following guides: - [Get started](/influxdb/v2.0/get-started) - [Write data](/influxdb/v2.0/write-data) - [Query data](/influxdb/v2.0/query-data)