Sync-lookahead seems a little bit confusing to some people, including me. Is it related to --lookahead-threads, too? What I can find to sync-lookahead
here isn't really up to date anymore.
What I understood is that it seems to have nothing to do with rc-lookahead (mbtree/vbv-lookahead).
Maybe someone can explain what exactly it does / what's the difference to rc-lookahead.