Copy to library takes 30 times longer than import
Calibre 2.58 on Ubuntu 14.04.
I have a large library >450k books. When I import books, I import into an empty library so I can edit metadata quickly. This includes, typically, switching Author and Title fields, correcting Authors with commas, setting language to English, eliminating dates from Author fields, etc. When finished, I can either import the books from the small library directory, or copy the books to the large library. The import loses some edits as it re-reads data from the files themselves. The library copy works better, but takes MUCH longer, like multiple days to import 4k files into the large library. I think the library copy should be faster, not much slower, as it should just be copying the metadata from the database to the other database. The import is re-reading the files and getting bad data again. The correcting edits then take much longer, as updating the large library takes a minute or so for each individual edit.