Glossary of Terms

Warning! This page documents an old version of InfluxDB, which is no longer actively developed. InfluxDB v1.2 is the most recent stable version of InfluxDB.

aggregation

An InfluxQL function that returns an aggregated value across a set of points. See InfluxQL Functions for a complete list of the available and upcoming aggregations.

Related entries: function, selector, transformation

cluster

A collection of servers running InfluxDB nodes. All nodes in a cluster have the same users, databases, retention policies, and continuous queries. See Clustering for how to set up an InfluxDB cluster.

Related entries: node, server

consensus node

A node running only the consensus service.

See Cluster Node Configuration.

Related entries: cluster, consensus service, data node, node, hybrid node

consensus service

The InfluxDB service that participates in the raft consensus group. A cluster must have at least three nodes running the consensus service (consensus or hybrid nodes), but it can have more. There should be an odd number of nodes running the consensus service in a cluster.

The number of consensus services that can fail before the cluster is degraded is ⌈n/2 + 1⌉ where n is the number of consensus services in the cluster. Thus, an even number of consensus services offer no additional redundancy or resiliency.

The consensus service ensures consistency across the cluster for node membership, databases, retention policies, users, continuous queries, shard metadata, and subscriptions.

See Cluster Node Configuration.

Related entries: cluster, consensus node, data service, node, hybrid node

continuous query (CQ)

An InfluxQL query that runs automatically and periodically within a database. Continuous queries require a function in the SELECT clause and must include a GROUP BY time() clause. See Continuous Queries.

Related entries: function

coordinator node

The node that receives write and query requests for the cluster.

Related entries: cluster, hinted handoff, node

data node

A node running only the data service.

See Cluster Node Configuration.

Related entries: cluster, consensus node, data service, node, hybrid node

data service

The InfluxDB service that persists time-series data to the node. A cluster must have at least one node (data or hybrid nodes) running the data service, but may have any number beyond one.

See Cluster Node Configuration.

Related entries: cluster, consensus node, consensus service, node, hybrid node

database

A logical container for users, retention policies, continuous queries, and time series data.

Related entries: continuous query, retention policy, user

duration

The attribute of the retention policy that determines how long InfluxDB stores data. Data older than the duration are automatically dropped from the database. See Database Management for how to set duration.

Related entries: replication factor, retention policy

field

The key-value pair in InfluxDB’s data structure that records metadata and the actual data value. Fields are required in InfluxDB’s data structure and they are not indexed - queries on field values scan all points that match the specified time range and, as a result, are not performant relative to tags.

Query tip: Compare fields to tags; tags are indexed.

Related entries: field key, field set, field value, tag

field key

The key part of the key-value pair that makes up a field. Field keys are strings and they store metadata.

Related entries: field, field set, field value, tag key

field set

The collection of field keys and field values on a point.

Related entries: field, field key, field value, point

field value

The value part of the key-value pair that makes up a field. Field values are the actual data; they can be strings, floats, integers, or booleans. A field value is always associated with a timestamp.

Field values are not indexed - queries on field values scan all points that match the specified time range and, as a result, are not performant.

Query tip: Compare field values to tag values; tag values are indexed.

Related entries: field, field key, field set, tag value, timestamp

function

InfluxQL aggregations, selectors, and transformations. See InfluxQL Functions for a complete list of InfluxQL functions.

Related entries: aggregation, selector, transformation

hinted handoff

A durable queue of data destined for a server which was unavailable at the time the data was received. Coordinating nodes temporarily store queued data when a target node for a write is down for a short period of time.

Related entries: cluster, node, server

hybrid node

A node running both the consensus and data services.

See Cluster Node Configuration.

Related entries: cluster, consensus node, consensus service, node, data node, data service

identifier

Tokens which refer to database names, retention policy names, user names, measurement names, tag keys, and field keys. See Query Language Specification.

Related entries: database, field key, measurement, retention policy, tag key, user

line protocol

The text based format for writing points to InfluxDB. See Line Protocol.

measurement

The part of InfluxDB’s structure that describes the data stored in the associated fields. Measurements are strings.

Related entries: field, series

metastore

Contains internal information about the status of the system. That includes user information, database and shard metadata, and which retention policies are enabled.

Related entries: database,retention policy,user

node

An independent influxd process.

Related entries: cluster, server

point

The part of InfluxDB’s data structure that consists of a single collection of fields in a series. Each point is uniquely identified by its series and timestamp.

You cannot store more than one point with the same timestamp in the same series. Instead, when you write a new point to the same series with the same timestamp as an existing point in that series, the field set becomes the union of the old field set and the new field set, where any ties go to the new field set. For an example, see Frequently Encountered Issues.

Related entries: field set, series, timestamp

query

An operation that retrieves data from InfluxDB. See Data Exploration, Schema Exploration, Database Management.

replication factor

The attribute of the retention policy that determines how many copies of the data are stored in the cluster. InfluxDB replicates data across N data nodes, where N is the replication factor.

To maintain data availability for queries, the replication factor should be less than or equal to the number of data nodes in the cluster:

  • Data are fully available when the replication factor is greater than the number of unavailable data nodes.
  • Data may be unavailable when the replication factor is less than the number of unavailable data nodes.

Note that there are no query performance benefits from replication. Replication is for ensuring data availability when a data node or nodes are unavailable. See Database Management for how to set the replication factor.

Related entries: cluster, duration, node, retention policy

retention policy (RP)

The part of InfluxDB’s data structure that describes for how long InfluxDB keeps data (duration) and how many copies of those data are stored in the cluster (replication factor). RPs are unique per database and along with the measurement and tag set define a series.

When you create a database, InfluxDB automatically creates a retention policy called default with an infinite duration and a replication factor set to the number of nodes in the cluster. See Database Management for retention policy management.

Related entries: duration, measurement, replication factor, series, tag set

schema

How the data are organized in InfluxDB. The fundamentals of the InfluxDB schema are databases, retention policies, series, measurements, tag keys, tag values, and field keys. See Schema Design for more information.

Related entries: database, field key, measurement, retention policy, series, tag key, tag value

selector

An InfluxQL function that returns a single point from the range of specified points. See InfluxQL Functions for a complete list of the available and upcoming selectors.

Related entries: aggregation, function, transformation

series

The collection of data in InfluxDB’s data structure that share a measurement, tag set, and retention policy.

Note: The field set is not part of the series identification!

Related entries: field set, measurement, retention policy, tag set

series cardinality

The count of all combinations of measurements and tags within a given data set. For example, take measurement mem_available with tags host and total_mem. If there are 35 different hosts and 15 different total_mem values then series cardinality for that measurement is 35 * 15 = 525. To calculate series cardinality for a database add the series cardinalities for the individual measurements together.

Related entries: tag set, measurement, tag key

server

A machine, virtual or physical, that is running InfluxDB. There should only be one InfluxDB process per server.

Related entries: cluster, node

tag

The key-value pair in InfluxDB’s data structure that records metadata. Tags are an optional part of InfluxDB’s data structure but they are useful for storing commonly-queried metadata; tags are indexed so queries on tags are performant. Query tip: Compare tags to fields; fields are not indexed.

Related entries: field, tag key, tag set, tag value

tag key

The key part of the key-value pair that makes up a tag. Tag keys are strings and they store metadata. Tag keys are indexed so queries on tag keys are performant.

Query tip: Compare tag keys to field keys; field keys are not indexed.

Related entries: field key, tag, tag set, tag value

tag set

The collection of tag keys and tag values on a point.

Related entries: point, series, tag, tag key, tag value

tag value

The value part of the key-value pair that makes up a tag. Tag values are strings and they store metadata. Tag values are indexed so queries on tag values are performant.

Related entries: tag, tag key, tag set

timestamp

The date and time associated with a point. All time in InfluxDB is UTC.

For how to specify time when writing data, see Write Syntax. For how to specify time when querying data, see Data Exploration.

Related entries: point

transformation

An InfluxQL function that returns a value or a set of values calculated from specified points, but does not return an aggregated value across those points. See InfluxQL Functions for a complete list of the available and upcoming aggregations.

Related entries: aggregation, function, selector

user

There are two kinds of users in InfluxDB:

  • Admin users have READ and WRITE access to all databases and full access to administrative queries and user management commands.
  • Non-admin users have READ, WRITE, or ALL (both READ and WRITE) access per database.

When authentication is enabled, InfluxDB only executes HTTP requests that are sent with a valid username and password. See Authentication and Authorization.