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:

SUGGESTED FOR 'PU':

Traversing objects is currently very costly, as every commit and tree must be 
loaded and parsed.  Much time and energy could be saved by caching metadata and 
topological info in an efficient, easily accessible manner.  Furthermore, this 
could improve git's interfacing potential, by providing a condensed summary of 
a repository's commit tree.

This is a series to implement such a revision caching mechanism, aptly named 
rev-cache.  The series will provide:
 - a core API to manipulate and traverse caches
 - an integration into the internal revision walker
 - a porcelain front-end providing access to users and (shell) applications
 - a series of tests to verify/demonstrate correctness
 - documentation of the API, porcelain and core concepts

In cold starts rev-cache has sped up packing and walking by a factor of 4, and 
over twice that on warm starts.  Some times on slax for the linux repository:

rev-list --all --objects >/dev/null
 default
   cold    1:13
   warm    0:43
 rev-cache'd
   cold    0:19
   warm    0:02

pack-objects --revs --all --stdout >/dev/null
 default
   cold    2:44
   warm    1:21
 rev-cache'd
   cold    0:44
   warm    0:10

Nice!

The mechanism is minimally intrusive: most of the changes take place in 
seperate files, and only a handful of git's existing functions are 
modified.

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

 Documentation/rev-cache.txt           |   51 +
 Documentation/technical/rev-cache.txt |  336 ++++++
 Makefile                              |    2 +
 blob.c                                |    1 +
 blob.h                                |    1 +
 builtin-rev-cache.c                   |  284 +++++
 builtin.h                             |    1 +
 commit.c                              |    3 +
 commit.h                              |    2 +
 git.c                                 |    1 +
 list-objects.c                        |   49 +-
 rev-cache.c                           | 1832 +++++++++++++++++++++++++++++++++
 revision.c                            |   89 ++-
 revision.h                            |   46 +-
 t/t6015-rev-cache-list.sh             |  228 ++++
 t/t6015-sha1-dump-diff.py             |   36 +

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.

Ciao,
Dscho