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POAre Git's pack files deltas rather than snapshots?
 

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    <p>One of the key differences between Git and most other version control systems is that the others tend to store commits as a series of deltas - changesets between one commit and the next. This seems logical, since it's the smallest possible amount of information to store about a commit. But the longer the commit history gets, the more calculation it takes to compare ranges of revisions.</p> <p>By contrast, Git stores a <strong>complete snapshot of the whole project in each revision</strong>. The reason this doesn't make the repo size grow dramatically with each commit is each file in the project is stored as a file in the Git subdirectory, named for the hash of its contents. So if the contents haven't changed, the hash hasn't changed, and the commit just points to the same file. And there are other optimizations as well.</p> <p>All this made sense to me until I stumbled on <a href="http://git-scm.com/book/en/v2/Git-Internals-Packfiles">this information about pack files</a>, into which Git puts data periodically to save space:</p> <blockquote> <p>In order to save that space, Git utilizes the packfile. This is a format where Git will only save the part that has changed in the second file, with a pointer to the file it is similar to.</p> </blockquote> <p><strong>Isn't this basically going back to storing deltas? If not, how is it different? How does this avoid subjecting Git to the same problems other version controls systems have?</strong></p> <p>For example, Subversion uses deltas, and rolling back 50 versions means undoing 50 diffs, whereas with Git you can just grab the appropriate snapshot. Unless git also stores 50 diffs in the packfiles... is there some mechanism that says "after some small number of deltas, we'll store a whole new snapshot" so that we don't pile up too large a changeset? How else might Git avoid the disadvantages of deltas?</p>
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    1. USNick Volynkin
    1. USNathan Long
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    1. COSee [pack-format.txt](http://www.kernel.org/pub/software/scm/git/docs/technical/pack-format.txt) and [pack-heuristics.txt](http://www.kernel.org/pub/software/scm/git/docs/technical/pack-heuristics.txt) in the documentation.
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      1. USJosh Lee
    2. CO@jleedev: Thanks for the links!
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      1. USPaŭlo Ebermann
    3. COlinks are broken now...
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      1. USThilo
 

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