Re: two questions about the format of loose object

From: Junio C Hamano <gitster@pobox.com>
Date: Dec 1, 2008, 08:25 UTC
Message-ID: <7voczws3np.fsf@gitster.siamese.dyndns.org>
In-Reply-To: <493399B7.5000505@gmail.com>

Liu Yubao <yubao.liu@gmail.com> writes:

Show 14 quoted lines

> In current implementation the loose objects are compressed:
>
>      loose object = deflate(typename + <space> + size + '\0' + data)
>
> In sha1_file.c:unpack_sha1_file():
> 	1) unpack_sha1_header() inflates first 8KB
>         2) parse_sha1_header() gets object's size
>         3) unpack_sha1_reset() allocates a (1+size) bytes buffer and
>            copy the first 8KB without header to it.
>
> * Question 1:
> Why not ...
> * Question 2:
> Why not ...

A hint for understanding why loose objects are compressed is that packfiles were invented much later in the history of git.

These are both good questions, and it might have made a difference if they were posed in early April 2005.

At this point, the plain and clear answer to both of these "Why not" questions is "because that is the way it is and it is costly to change them now in thousands of repositories people use every day."

In other words, it is not interesting anymore to raise these questions now, especially as a suggestion to change the system, unless they are accompanied by arguments that convinces everybody that the cost of such a change outweighs the benefits, and a clear transition plans how to upgrade everybody's existing repositories without any pain.