[with patch, positive review] sage-clone should use hard links for the build directory

[burcin]

We copy the build directory when we're cloning the tree. This wastes disk space, and makes switching between branches slow, since new files need to be loaded from disk while the previous ones might already be in the cache.

Attached patch to the scripts repository changes the sage-clone script to hard link the build directory. On my laptop this saves >450 MB per clone.

burcin@karr ~/sage/sage-3.3/devel $ du -sh sage-*
593M    sage-hl
125M    sage-hl1
557M    sage-main

Also the time to clone on my laptop goes from:

real    0m14.709s
user    0m4.640s
sys     0m1.924s

to

real    0m6.100s
user    0m4.712s
sys     0m0.928s

about 2.8 seconds of which is spent in the sage -b step.

Unfortunately, hard linking the .c, .cpp, and .h files doesn't work. This might be a problem with how cython handles its output when the output file is already present. This would save another ~100MB if it works.

[burcin]

make sage-clone use hard links

[mabshoff]

I don't think we want this in a critical stable release :)

Cheers,

Michael

[robertwb]

Cython 0.11 will make hard links on .c and .cpp files work too.

 http://trac.cython.org/cython_trac/ticket/220 and #4987

[burcin]

rebased for 4.0.1

[burcin]

attachment:trac_5350-clone_hardlink-take2.patch is a new version of the patch. It is rebased to 4.0.1. We now use hard links for autogenerated cython files and documentation output too.

[rlm]

Everything works fine, and the speedup is impressive, but I agree that a two-digit release might not be appropriate for something so invasive.