= Improving performance for Trac's git support

== Using python bindings for git rather than the git command-line

This could be an alternative backend that would avoid the cost of spawning git executables and parsing their standard output.

The trade-offs could be the following, bindings vs. command-line:
 - (+) faster (but how much?)
 - (?) robustness
   - (+) no pipe handling and dangling processes (is this still problematic?)
   - (-) crashes?
 - (-) memory usage (risk of memory leaks?)

Peter Stuge started a conversion of the backend, see his early work in his [http://git.stuge.se/?p=trac.git;a=summary;js=1 pygit2wip] branch.


=== Installation

First you'll need to install the git bindings for Python:
 - [https://github.com/libgit2/libgit2 libgit2]
 - [https://github.com/libgit2/pygit2 pygit2]
And for building `libgit2`, you'll need [http://cmake.org cmake].

==== Windows build instructions, for Python 2.6 or 2.7 with VC9 #pygit2-msvc9

{{{
$ git clone https://github.com/libgit2/libgit2.git
$ cd libgit2
}}}
Now set the `LIBGIT2` environment variable to the place you want to install `libgit2` (this environment variable is expected to be set by `pygit2`):
{{{
$ export LIBGIT2=C:/Dev/libgit2-vc9
}}}
if you live in a msysgit bash shell,
or:
{{{
> set LIBGIT2=C:/Dev/libgit2-vc9
}}}
if you're forced to use a cmd.exe...

Then download the [attachment:libgit2-msvc9.diff] patch, apply it, build and install `libgit2` like this:
{{{
$ patch -p1 < libgit2-msvc9.diff
$ mkdir build-msvc9
$ cd build-msvc9
$ cmake -G "Visual Studio 9 2008" .. -DCMAKE_INSTALL_PREFIX=$LIBGIT2
-- Check for working C compiler using: Visual Studio 9 2008
-- Check for working C compiler using: Visual Studio 9 2008 -- works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Found PythonInterp: C:/Dev/Python272/python.exe (found version "2.7.2")
-- Configuring done
-- Generating done
-- Build files have been written to: C:/Workspace/src/git/libgit2/build-msvc9
$ cmake --config Release --build . --target install
}}}
(replace `$LIBGIT2` with `%LIBGIT2%` if you're in a `cmd.exe`)

At this point you're ready to build the bindings themselves:
{{{
$ git clone https://github.com/libgit2/pygit2
$ cd pygit2
$ ls $LIBGIT2
bin include lib
$ python setup.py install
}}}

Note about the tests:
{{{
$ python setup.py test --args\ -v
}}}
with 0.17, I get one error (`test_read_tree`) and ... several crashes (`test_new_repo`, `test_write`, `test_status`, and nearly all tests in `test_diff.py`).