Subject: Re: [ANNOUNCE] Stacked GIT 0.7

From: Catalin Marinas <[email-masked]>
Date: Mon, 03 Oct 2005 15:44:12 +0100

Catalin Marinas <[email-masked]> wrote:
> After some tests, it looks like 'git-diff-tree -p ... | git-apply
> --index' is about 3 times faster than 'git-read-tree -m' (in the best
> case for git-read-tree with minor modifications of the base). It now
> takes ~0.5s to push a single patch (compared to ~1.5s).

And that's the patch for whoever wants to try. I will also add it to
the repository tonight:

Optimise 'push' to use git-apply instead of git-read-tree

With this patch, 'push' will use 'git-diff-tree | git-apply' first. If this
operation fails, it will fall back to the three-way merge with
git-read-tree.

Signed-off-by: Catalin Marinas <[email-masked]>
---

 stgit/git.py   |    9 +++++++++
 stgit/stack.py |   19 +++++++++++--------
 2 files changed, 20 insertions(+), 8 deletions(-)

diff --git a/stgit/git.py b/stgit/git.py
--- a/stgit/git.py
+++ b/stgit/git.py
@@ -355,6 +355,15 @@ def commit(message, files = [], parents 
 
     return commit_id
 
+def apply_diff(rev1, rev2):
+    """Apply the diff between rev1 and rev2 onto the current
+    index. This function doesn't need to raise an exception since it
+    is only used for fast-pushing a patch. If this operation fails,
+    the pushing would fall back to the three-way merge.
+    """
+    return os.system('git-diff-tree -p %s %s | git-apply --index 2> /dev/null'
+                     % (rev1, rev2)) == 0
+
 def merge(base, head1, head2):
     """Perform a 3-way merge between base, head1 and head2 into the
     local tree
diff --git a/stgit/stack.py b/stgit/stack.py
--- a/stgit/stack.py
+++ b/stgit/stack.py
@@ -598,14 +598,17 @@ class Series:
             # The current patch is empty after merge.
             patch.set_bottom(head, backup = True)
             patch.set_top(head, backup = True)
-            # merge/refresh can fail but the patch needs to be pushed
-            try:
-                git.merge(bottom, head, top)
-            except git.GitException, ex:
-                print >> sys.stderr, \
-                      'The merge failed during "push". ' \
-                      'Use "refresh" after fixing the conflicts'
-                pass
+
+            # Try the fast applying first. If this fails, fall back to the
+            # three-way merge
+            if not git.apply_diff(bottom, top):
+                # merge can fail but the patch needs to be pushed
+                try:
+                    git.merge(bottom, head, top)
+                except git.GitException, ex:
+                    print >> sys.stderr, \
+                          'The merge failed during "push". ' \
+                          'Use "refresh" after fixing the conflicts'
 
         append_string(self.__applied_file, name)

-- 
Catalin