Here is a list of all documented struct and union fields with links to the struct/union documentation for each field:

app_name : newrelic_app_config_t
collection : newrelic_datastore_segment_params_t
database_name : newrelic_datastore_segment_params_t
database_name_reporting : newrelic_datastore_segment_config_t
datastore_reporting : newrelic_transaction_tracer_config_t
datastore_tracer : newrelic_app_config_t
distributed_tracing : newrelic_app_config_t
duration_us : newrelic_transaction_tracer_config_t
enabled : newrelic_distributed_tracing_config_t , newrelic_span_event_config_t , newrelic_transaction_tracer_config_t
host : newrelic_datastore_segment_params_t
instance_reporting : newrelic_datastore_segment_config_t
library : newrelic_external_segment_params_t
license_key : newrelic_app_config_t
log_filename : newrelic_app_config_t
log_level : newrelic_app_config_t
operation : newrelic_datastore_segment_params_t
port_path_or_id : newrelic_datastore_segment_params_t
procedure : newrelic_external_segment_params_t
product : newrelic_datastore_segment_params_t
query : newrelic_datastore_segment_params_t
record_sql : newrelic_transaction_tracer_config_t
redirect_collector : newrelic_app_config_t
span_events : newrelic_app_config_t
stack_trace_threshold_us : newrelic_transaction_tracer_config_t
threshold : newrelic_transaction_tracer_config_t
threshold_us : newrelic_transaction_tracer_config_t
transaction_tracer : newrelic_app_config_t
uri : newrelic_external_segment_params_t