Subject: [PATCH] git-p4: speed up search for branch parent

From: "Joachim Kuebart via GitGitGadget" <[email-masked]>
Date: Wed, 28 Apr 2021 20:06:56 +0000

From: Joachim Kuebart <[email-masked]>

Previously, the code iterated through the parent branch commits and
compared each one to the target tree using diff-tree.

This patch outputs the revision's tree hash along with the commit hash,
thereby saving the diff-tree invocation. This results in a considerable
speed-up, at least on Windows.

Signed-off-by: Joachim Kuebart <[email-masked]>
---
    git-p4: speed up search for branch parent
    
    Previously, the code iterated through the parent branch commits and
    compared each one to the target tree using diff-tree.
    
    This patch outputs the revision's tree hash along with the commit hash,
    thereby saving the diff-tree invocation. This results in a considerable
    speed-up, at least on Windows.
    
    Signed-off-by: Joachim Kuebart [email-masked]

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-1013%2Fjkuebart%2Fp4-faster-parent-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-1013/jkuebart/p4-faster-parent-v1
Pull-Request: https://github.com/git/git/pull/1013

 git-p4.py | 22 +++++++++++-----------
 1 file changed, 11 insertions(+), 11 deletions(-)

diff --git a/git-p4.py b/git-p4.py
index 09c9e93ac401..dbe94e6fb83b 100755
--- a/git-p4.py
+++ b/git-p4.py
@@ -3600,19 +3600,19 @@ def importNewBranch(self, branch, maxChange):
         return True
 
     def searchParent(self, parent, branch, target):
-        parentFound = False
-        for blob in read_pipe_lines(["git", "rev-list", "--reverse",
+        for tree in read_pipe_lines(["git", "rev-parse",
+                                     "{}^{{tree}}".format(target)]):
+            targetTree = tree.strip()
+        for blob in read_pipe_lines(["git", "rev-list", "--format=%H %T",
                                      "--no-merges", parent]):
-            blob = blob.strip()
-            if len(read_pipe(["git", "diff-tree", blob, target])) == 0:
-                parentFound = True
+            if blob[:7] == "commit ":
+                continue
+            blob = blob.strip().split(" ")
+            if blob[1] == targetTree:
                 if self.verbose:
-                    print("Found parent of %s in commit %s" % (branch, blob))
-                break
-        if parentFound:
-            return blob
-        else:
-            return None
+                    print("Found parent of %s in commit %s" % (branch, blob[0]))
+                return blob[0]
+        return None
 
     def importChanges(self, changes, origin_revision=0):
         cnt = 1

base-commit: 311531c9de557d25ac087c1637818bd2aad6eb3a
-- 
gitgitgadget