On Thu, Jan 21, 2010 at 2:51 PM, Andrey Kuzmin
<andrey.v.kuz...@gmail.com> wrote:
> Looking at dedupe code, I noticed that on-disk DDT entries are
> compressed less efficiently than possible: key is not compressed at
> all (I'd expect roughly 2:1 compression ration with sha256 data),
A cryptographic hash such as sha256 should not be compressible. A
trivial example shows this to be the case:
for i in {1..10000} ; do
echo $i | openssl dgst -sha256 -binary
done > /tmp/sha256
$ gzip -c <sha256 >sha256.gz
$ compress -c <sha256 >sha256.Z
$ bzip2 -c <sha256 >sha256.bz2
$ ls -go sha256*
-rw-r--r-- 1 320000 Jan 22 04:13 sha256
-rw-r--r-- 1 428411 Jan 22 04:14 sha256.Z
-rw-r--r-- 1 321846 Jan 22 04:14 sha256.bz2
-rw-r--r-- 1 320068 Jan 22 04:14 sha256.gz
--
Mike Gerdts
http://mgerdts.blogspot.com/
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