[mrmikel]

Seems like I remember reading that Kovid said that he does as little as possible compared to Sigil. The whole book is checked on open always in Sigil or laid out in Sigil format or something. I'll check over in the new forum and see if I can find it.

..found it:

That's how the new database backend is faster than the old, despite actually being thread safe, which involves overhead for locking. And it's why the editor is so fast. By using various, rather nifty tricks, I was able to make the editor fast. The basic idea is to do as little as possible and that, only when absolutely necessary.

For example, Sigil parses all files when the book is first opened and renames them. There's absolutely no need to do that. Instead, calibre works with html even if it is not strictly valid.

Another trick is that the parsing and fixing of html before displaying in the preview panel happens in a separate process, so it keeps the editor itself feeling responsive, while the heavy works happens on a different CPU core.