Re: [PATCH] repack: add -F option that passes --no-reuse-delta to pack-objects

On Mon, 27 Sep 2010, Jan Krüger wrote:

In 479b56ba ('make "repack -f" imply "pack-objects --no-reuse-object"'),
git repack -f was changed to include recompressing all objects on the
zlib level on the assumption that if the user wants to spend that much
time already, some more time won't hurt (and recompressing is useful if
the user changed the zlib compression level).

However, "some more time" can be quite long with very big repositories,
so some users are going to appreciate being able to choose. Hence, this
adds a new -F option that uses the old behaviour of recalculating deltas
only and keeping the zlib compression intact.

Measurements taken using this patch on a current clone of git.git
indicate a 17% decrease in time being made available to users:

git repack -Adf  38.79s user 0.56s system 133% cpu 29.394 total
git repack -AdF  34.84s user 0.56s system 145% cpu 24.388 total

Signed-off-by: Jan Krüger <redacted>
---

The concrete case that prompted me to write this patch was a repository
of 25 GB that some guys were trying to repack. 17% of the time needed to
repack -f that much data is... substantial.

Discussion point: it might make more sense to switch the meanings
around, making -F do the 'bigger' routine and reverting -f to what it
used to be. I don't feel strongly about that, however.

That's exactly what I was about to propose before I read through your 
email down to this part.

I personally don't find --no-reuse-object particularly useful.  I hardly 
imagine that people are changing the pack compression level that often 
if at all.  So I doubt moving the current --no-reuse-object behavior to 
-F and reverting -f to  --no-reuse-delta would cause any serious 
inconvenience.  It certainly won't _break_ anything.  So you have my ACK 
to do that change.

In addition to that change, perhaps a note could be added to the 
documentation for pack.compression indicating that for the new setting 
to take effect for existing packs, they must be repacked with -F.


Nicolas