Re: [PATCH v2 2/2] index-pack: kill union delta_base to save memory

From: Duy Nguyen <pclouds@gmail.com>
Date: Feb 28, 2015, 11:44 UTC
Message-ID: <CACsJy8A3MxpQRwboVjyv7akvzgf3y23ZsnAaxuHXkm2U=tUk0A@mail.gmail.com>
In-Reply-To: <xmqqzj7zhx31.fsf@gitster.dls.corp.google.com>

On Sat, Feb 28, 2015 at 4:18 AM, Junio C Hamano <gitster@pobox.com> wrote:

Show 8 quoted lines

> Nguyễn Thái Ngọc Duy  <pclouds@gmail.com> writes:
>
>> Notice that with "recent" Git versions, ofs-delta objects are
>> preferred over ref-delta objects and ref-delta objects have no reason
>> to be present in a clone pack.
>
> It is true that we try to use ofs-delta as much as possible, but
> where does "have no reason to be present" come from?

Lack of knowledge, or writing without double checking the code.

> When an object cannot be represented as an ofs-delta (which can only
> refer backwards), don't we use ref-delta, instead of storing it as a
> deflated-full object?

Ah I think you're right. The decision to choose ofs-delta in pack-objects is if ofs-delta is enabled _and_ the offset to base is available (i.e. base is already written).

Show 7 quoted lines

> Probably "Not so ancient versions of Git tries to use ofs-delta
> encoding whenever possible, so it is expected that objects encoded
> using ref-delta are minority" may be closer to the truth.  And that
> observation does justify why using two separate pools (one with
> 8-byte entries for ofs-delta, the other with 20-byte entries for
> ref-delta) is a better idean than using one pool with 20-byte
> entries for both kinds.

Yes. Looks good. Should I send a patch, or you fix the commit message locally?

-- 
Duy