How do you git archive a branch using gzip with highest compression level?

2
votes

I'm trying to git archive a branch using gzip with the highest level compression (9) but it seems to not compress at that level. Here is my command:

git -C /home/user/example.com/ archive --format tar -o /home/user/site_backups/develop-`date +%Y-%m-%dT%H%M`.tar develop | gzip -9

It creates the tar file but the size is over 100MB compared to a zip that was compressed at 86MB using this command:

git -C /home/user/example.com/ archive --format zip -o /home/user/site_backups/develop-`date +%Y-%m-%dT%H%M`.zip develop

Can the output file be compressed more? What am I doing wrong?

1
gitsshzipgzipgit-archive

1 Answers

1
votes

Nowadays (4 years later), the command would be:

git -C /home/user/example.com/ archive --format tgz -19 -o /home/user/site_backups/develop-`date +%Y-%m-%dT%H%M`.tar develop

With Git 2.30 (Q1 2021), "git archive"(man) now allows compression level higher than "-9" when generating tar.gz output.

See commit cde8ea9 (09 Nov 2020) by René Scharfe (rscharfe).
(Merged by Junio C Hamano -- gitster -- in commit ede4d63, 18 Nov 2020)

archive: support compression levels beyond 9

Signed-off-by: René Scharfe

Compression programs like zip, gzip, bzip2 and xz allow to adjust the trade-off between CPU cost and size gain with numerical options from -1 for fast compression and -9 for high compression ratio.
zip also accepts -0 for storing files verbatim.
git archive(man) directly support these single-digit compression levels for ZIP output and passes them to filters like gzip.

Zstandard additionally supports compression level options -10 to -19, or up to -22 with --ultra.
This seems to work with git archive(man) in most cases, e.g. it will produce an archive with -19 without complaining, but since it only supports single-digit compression level options this is the same as -1 -9 and thus -9.

Allow git archive(man) to accept multi-digit compression levels to support the full range supported by zstd.
Explicitly reject them for the ZIP format, as otherwise deflateInit2() would just fail with a somewhat cryptic "stream consistency error".