Re: Fwd: what is a snapshot?

From: Jakub Narębski <jnareb@gmail.com>
Date: Jun 29, 2016, 19:28 UTC
Message-ID: <57742174.9020309@gmail.com>
In-Reply-To: <CAHWPVgMWeHoD5vTiFJ1gsm2hS74LK7j4npVVbOZeR43cX3qWXw@mail.gmail.com>

W dniu 2016-06-19 o 16:15, Ovatta Bianca pisze:

Show 5 quoted lines

> I read in every comparison of git vs other version control systems,
> that git does not record differences but takes "snapshots"
> I was wondering what a "snapshot" is ? Does git store at every commit
> the entire files which have been modified even if only a few bytes
> were changed out of a large file?

There are two things: the conceptual level, and actual storage. On the conceptual level, object representing revisions (commit) refer to object representing top directory (tree) of a project, that is a snapshot of a project state at given revision.

On the storage level, Git has two types of object storage. In "loose" format (used for new objects), each object is stored as a separate file. This is not as wasteful as you think: first, there is deduplication, that is each version of a file is stored only once. Second, contents (usually text) is stored compressed.

In "packed" format (nowadays Git automatically repacks from "loose" to "packed" when it looks like it is needed) there is additional libxdiff-like deltafication. In this format Git stores differences (well, it also ensures that delta chain doesn't gets too long).

HTH

-- 
Jakub Narębski