I have a query which is quite fast, but I see in the query plan (Using the client GUI) that the printing is very very slow, even when the number of hits is zero.

I wonder what it means, and it is a problem.

Due to the iterative evaluation pattern, it is often not possible to clearly separate the evaluation and printing/serialization steps. Feel free to show me with a query that leads to this pattern, and I may be able to give you more information.