In New Relic, attributes are key-value pairs containing information that determines the properties of an event or transaction. These key-value pairs can help you gain greater insight into your application and query your data.
Before creating custom attributes, review New Relic's list of reserved terms used by NRQL. Otherwise unexpected results may occur.
To add custom attributes to your C application, call one of the attribute functions in the C SDK API; for example,
newrelic_add_attribute_double(). The key name for your custom attribute depends on what you specify when you call the function.