Re: git-fetching from a big repository is slow

[Shawn Pearce <spearce@spearce.org>]

Geert Bosch <bosch@adacore.com> wrote:
> Such special magic based on filenames is always a bad idea. Tomorrow  
> somebody
> comes with .zip files (oh, and of course .ZIP), then it's .jpg's other
> compressed content. In the end git will be doing lots of magic and  
> still perform
> badly on unknown compressed content.
> 
> There is a very simple way of detecting compressed files: just look  
> at the
> size of the compressed blob and compare against the size of the  
> expanded blob.
> If the compressed blob has a non-trivial size which is close to the  
> expanded
> size, assume the file is not interesting as source or target for deltas.
> 
> Example:
>    if (compressed_size > expanded_size / 4 * 3 + 1024) {
>      /* don't try to deltify if blob doesn't compress well */
>      return ...;
>    }

And yet I get good delta compression on a number of ZIP formatted
files which don't get good additional zlib compression (<3%).
Doing the above would cause those packfiles to explode to about
10x their current size.

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