Data-provider callbacks are invoked in copy-config

It was mentioned in the confd user guide, that data-provider callbacks will be invoked during copy-config operation.

“15.4.1. Error Handling
When ConfD processes , , and requests, the resulting data set can be very large. To avoid buffering huge amounts of data, ConfD streams the reply to the client as it traverses the data tree and calls data provider functions to retrieve the data.”

Why data-provider are invoked during copy-config and get-config. Please clarify.

The data-provider mention here is where the configuration comes from.
If Configuration is stored in CDB, then it will be fetched from CDB, using internal callbacks
If Configuration is stored outside of CDB, user written callbacks will be used to fetch the data.

In both copy-config and get-config, configuration has to be read first.