I have a bib file with 1086 entries and biber requires 6 seconds to process it, which is alot w.r.t. the overall compile time of my document.

I propose to add the following features to biber.

• biber should (probably based on some parameter) check first whether the list of used keys has changed: if not, biber should abort immediately.

• biber should (probably based on some parameter) export a bib file containing the used references only.
  Then, if only references have been removed, biber should (probably based on some parameter) reuse the small bib file containing the used references only to generate the bbl file.