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Re: just curious: what influences a commit hash?

From
MEMatt Enright <awickedshimmy@gmail.com>
Date
Mar 5, 2009, 07:25 UTC
Message-ID
<1236237939.2421.38.camel@virgil>
In-Reply-To
<20090305063632.42880@gmx.net>
On Thu, 2009-03-05 at 07:36 +0100, stoecher@gmx.at wrote:
Show 5 quoted lines
> Hi,
> 
> being new to git I did some experiments with commits looking at the hashes. What I observed:
> * The same commit (same file, same committer, same message) into different empty repositories (git init) gives different hashes. So I assume that also the time of the commit influences the hash. Is this intended? For what reason?
> * Having created two repositories exactly the same way (the history is the same except for the commit times and hashes) I applied the same patch (using git am) and again I got different hashes for these commits. So in some way also the repository/branch influences the hash of a commit!?

This should be expected if the initial hashes in the history are different. The hash of a commit is based also on the hashes of all parent commits - in this way git 'protects' the repository history by guaranteeing that if two objects have the same hash, they will come from the same history. So the second issue is a consequence of the first, though I am not certain why the first occurs (if the file contents and size are the same, I would expect the hash for the blob/tree to be the same - maybe due to git's special handling of initial commits?)

Show 6 quoted lines
> From reading the Git user's manual, chapter 10, object storage format, I was not expecting this. Can someone explain or give a link to a more detailed description?
> 
> thank you,
> 
> Wolfgang
>
Previous: stoecher@gmx.atNext: Uwe Kleine-König
Message 2 of 4 in “just curious: what influences a commit hash?”
  1. stoecher@gmx.atMar 5, 2009
  2. Matt EnrightMar 5, 2009
  3. Uwe Kleine-KönigMar 5, 2009
  4. Matthieu MoyMar 5, 2009

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