Re: [PATCH 0/5] Suggested for PU: revision caching system to significantly speed up packing/walking

Hi,

On Thu, 6 Aug 2009, Nick Edelen wrote:

quoted

Sorry, I forgot the details, could you quickly remind me why these 
caches are not in the pack index files?

Er, I'm not sure what you mean.  Are you asking why these revision 
caches are required if we have a pack index, or why they aren't in the 
pack index, or something different?  I'm thinking probably the second:

Yep.

the short answer is that cache slices are totally independant of pack 
files.

My idea with that was that you already have a SHA-1 map in the pack index, 
and if all you want to be able to accelerate the revision walker, you'd 
probably need something that adds yet another mapping, from commit to 
parents and tree, and from tree to sub-tree and blob (so you can avoid 
unpacking commit and tree objects).

I just thought that it could be more efficient to do it at the time the 
pack index is written _anyway_, as nothing will change in the pack after 
that anyway.

But I guess I can answer my question easily myself: the boundary commits 
will not be handled that way.

Still, there is some redundancy between the pack index and your cache, as 
you have to write out the whole list of SHA-1s all over again.  I guess it 
is time to look at the code instead of asking stupid questions.

It might be possible to somehow merge revision cache slices with pack 
indexes, but I don't think it'd be a very suitable modification.  The 
rev-cache slices are meant to act almost like topo-relation pack files: 
new slices are simply new files, seperate slice files can be fused 
("repacked") into a larger one, the index is a (recreatable) single file 
associating file (positions) with objects.  The format was geared to 
reducing potential cache/data loss and preventing overly large cache 
slices.

quoted

quoted

Hmpf.

We got rid of the last Python script in Git a long time ago, but now 
two different patch series try to sneak that dependency (at least for 
testing) back in.

That's all the worse because we cannot use Python in msysGit, and 
Windows should be a platform benefitting dramatically from your work.

In fact, the test the script performs could be easily rephrased with 
"sort", "uniq" and "comm". OTOH: If the walker is supposed to return 
the exact same orderd list of commits you can just use test_cmp.

The language that script is written in isn't important.  I originally
wrote it in python because I wanted something quick and wasn't much of
a sh guru (sorry :-/ ).  As Micheal said I've no doubt it can easily
be converted to shell script

That is not what I wanted to hear.

-- in fact, I'll try to get a shell version working today.

That is.

Thanks,
Dscho