Jakub Narebski  wrote:

quoted text
> Nicolas Pitre  writes:

> > On Tue, 12 Aug 2008, Geert Bosch wrote:

> >

> > > One nice optimization we could do for those pesky binary large objects

> > > (like PDF, JPG and GZIP-ed data), is to detect such files and revert

> > > to compression level 0. This should be especially beneficial

> > > since already compressed data takes most time to compress again.

> >

> > That would be a good thing indeed.

>

> Perhaps take a sample of some given size and calculate entropy in it?

> Or just simply add gitattribute for per file compression ratio...

Estimating the entropy would make it "just magic".  Most of Git is

"just magic" so that's a good direction to take.  I'm not familiar

enough with the PDF/JPG/GZIP/ZIP stream formats to know what the

first 4-8k looks like to know if it would give a good indication

of being already compressed.
Though I'd imagine looking at the first 4k should be sufficient

for any compressed file.  Having a header composed of 4k of _text_

before binary compressed data would be nuts.  Or a git-bundle with

a large refs listing.  ;-)
Using a gitattribute inside of pack-objects is not "simple".

We currently only support reading attributes from the working

directory if I recall correctly.  pack-objects may not have a

working directory.
Hence, "just magic" is probably the better route.
--

Shawn.

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