From: Jonathan Tan <jonathantanmy@google.com>
Date: Wed, 08 Aug 2018 18:45:44 GMT
Subject: Re: [PATCH 2/2] repack: repack promisor objects if -a or -A is set
Message-ID: <20180808184544.120498-1-jonathantanmy@google.com>
In-Reply-To: <xmqqy3dhiu08.fsf@gitster-ct.c.googlers.com>

> But what to delta against what else is determined by the pathname
> info, which is now lost by enumerating objects without tree/history
> walking.  By giving phoney pathnames to objects while enumerating
> them in offset order and giving similar pathnames to objects closer
> to each other, I was hoping that better bases will likely to be in
> the same window.  The order in which objects are prepared and fed to
> try_delta() is "group by type, and then sort by path-hash (major
> key) and size (descending order, used as minor key)", so that
> the largest among similarly named blobs is stored as base and other
> blobs with similar name try to become delta against that one.

Thanks for the patient explanation - I think I see it now. If we
enumerate in pack order and pass "<sha-1> <fake-name>" instead of
"<sha-1>" to pack-objects in such a way that we make pack-objects sort
by {type -> pack-order -> size} instead of {type -> size}, we can
hopefully get better deltas. I'll write a NEEDSWORK similar to this.

I'll send a reroll later today.