Re: [PATCHv4 08/12] Teach the notes lookup code to parse notes trees with various fanout schemes

["Shawn O. Pearce" <spearce@spearce.org>]

Junio C Hamano <gitster@pobox.com> wrote:
> Johan Herland <johan@herland.net> writes:
> > 2. Simply decide on a constant 2/2/36 fanout.
> 
> I thought it was Gitney who suggested to use a top-level fan-out based on
> the committer-date.  If you typically have already parsed the commit when
> you want to look up notes objects for it, it won't have extra overhead,
> and when looking at only recent history it will only need to access a
> small subset of trees.  I thought it was a neat idea (except that the
> question becomes what the granularity of the top level fan-out should
> be---one a day?  one a month?---the optimum would depend on commit
> density).  Was that idea shot down for some reason?

Yea, it was me.  I still think it might be a useful idea, since
it allows you better density of loading notes when parsing the
recent commits.  In theory the last 256 commits can easly be in
each of the 2/ fanout buckets, making 2/38 pointless for reducing
the search space.  Commit date on the other hand can probably force
all of them into the same bucket, making it easy to have the last
256 commits in cache, from a single bucket.

But I thought you shot it down, by saying that we also wanted to
support notes on blobs.  I happen to see no value in a note on
a blob, a blob alone doesn't make much sense without at least an
annotated tag or commit to provide it some named context, and the
latter two have dates.

-- 
Shawn.