Design your schema

Schema design can have a significant impact on both write and query performance in your InfluxDB cluster. The items below cover high-level considerations and recommendation. For detailed recommendations, see Schema design recommendations.

Understand the difference between tags and fields

In the InfluxDB data structure, there are three main “categories” of information–timestamps, tags, and fields. Understanding the difference between what should be a tag and what should be a field is important when designing your schema.

Use the following guidelines to determine what should be tags versus fields:

• Use tags to store metadata that provides information about the source or context of the data.
• Use fields to store measured values.
• Field values typically change over time. Tag values do not.
• Tag values can only be strings.
• Field values can be any of the following data types:
  • Integer
  • Unsigned integer
  • Float
  • String
  • Boolean

For more information, see Tags versus fields.

Schema restrictions

InfluxDB enforces the following schema restrictions:

• You cannot use the same name for a tag and a field in the same table.
• There is a limit to the number of columns you can store in a table. By default, tables can have up to 250 columns.

For more information, see InfluxDB schema restrictions.

Design for performance

The following guidelines help to ensure write and query performance:

• Avoid wide schemas: A wide schema is one with a large number of columns (tags and fields).
• Avoid sparse schemas: A sparse schema is one where, for many rows, columns contain null values.
• Keep table schemas homogenous: A homogenous table schema is one where every row has values for all tags and fields.
• Use the best data type for your data: Write integers as integers, decimals as floats, and booleans as booleans. Queries against a field that stores integers outperforms a query against string data.

Design for query simplicity

The following guidelines help to ensure that, when querying data, the schema makes it easy to write queries:

• Keep table names, tags, and fields simple: Use one tag or one field for each data attribute. If your source data contains multiple data attributes in a single parameter, split each attribute into its own tag or field.
• Avoid keywords and special characters: Reserved keywords or special characters in table names, tag keys, and field keys makes writing queries more complex.