Nils Dagsson Moskopp <nils@dieweltistgarnichtso.net> writes:

>
> mjw1009 can reproduce if the from-query contains an "@" and thinks the
> problem may be "something deeper down in notmuch (actually probably in
> xapian)".

My own experiments contradict that (see attached patch for a test to
run). The exact address is about twice as fast to count on both of my
machines, which matches the amount of I/O. FWIW, my SSD based laptop is
about 10x faster (compared to a similarly specced desktop with HD) for
both of them, which kindof reinforces how I/O bound this is.  

Replacing 'count' with 'search' gives pretty similar relative behaviour,
although much slower since it seems to do about 10x I/O.  

Finally after an initial "notmuch tag +fromlinus
from:torvalds@linux-foundation.org", "notmuch count tag:fromlinus" seems
to be about 5-10x faster than "notmuch count
from:torvalds@linux-foundation.org".  So that might be a workaround for
some people.

To sum up, I think the underlying question is whether the amount of I/O
that count does can be reduced when using non-boolean query terms.