[PATCH] allow to not sort the search results

[Olly Betts]

Sebastian Spaeth writes:
> On 2010-04-14, Jason White wrote:
> > > Also add a --sort=unsorted command line option to notmuch search to test
> > > this.
> > 
> > Does this provide relevance-ranked search results? I think relevance ranking
> > is the Xapian default if a sort order isn't specified. 
> 
> Yes, by default it is using sort_by_relevance, so "unsorted" implies
> just that. (in fact, a previous incarnation of this patch called it
> --sort=relevance)

Except notmuch (at least in the code I've looked at) sets the weighting scheme
to BoolWeight, so the ordering is actually just the raw docid ordering
(BoolWeight gives all matching docs a weight of 0).

> I would be happy to have it called --sort=relevance too, the unsorted
> points out potential performance improvements a bit better, IMHO
> (although they seem to be really small with a warm cache).

When using the results of a search to add/remove tags, there's likely to be
an additional win from --sort=unsorted as documents will now be processed
in docid order which will tend to have a more cache friendly locality of
access.

Also, sorting by relevance requires more calculations and may require fetching
additional data (document length for example).

So I think it would make sense for --sort=relevance and --sort=unsorted to be
separate options.

Cheers,
    Olly