[PATCH 11/11] Improve merge performance by avoiding in-index merges.
- From
Shawn O. Pearce <spearce@spearce.org>
- Date
- Dec 28, 2006, 07:35 UTC
- Message-ID
- <20061228073534.GK17867@spearce.org>
- In-Reply-To
- <9847899e4ba836980dbfed6d0ea1c82f31f21456.1167290864.git.spearce@spearce.org>
In the early days of Git we performed a 3-way read-tree based merge before attempting any specific merge strategy, as our core merge strategies of merge-one-file and merge-recursive were slower script based programs which took far longer to execute. This was a good performance optimization in the past, as most merges were able to be handled strictly by `read-tree -m -u`.
However now that merge-recursive is a C based program which performs a full 3-way read-tree before it starts running we need to pay the cost of the 3-way read-tree twice if we have to do any sort of file level merging. This slows down some classes of simple merges which `read-tree -m -u` could not handle but which merge-recursive does automatically.
For a really trivial merge which can be handled entirely by `read-tree -m -u`, skipping the read-tree and just going directly into merge-recursive saves on average 50 ms on my PowerPC G4 system. May sound odd, but it does appear to be true.
In a really simple merge which needs to use merge-recursive to handle a file that was modified on both branches, skipping the read-tree in git-merge saves on average almost 100 ms (on the same PowerPC G4) as we avoid doing some work twice.
We only avoid `read-tree -m -u` if the only strategy to use is merge-recursive, as not all merge strategies perform as well as merge-recursive does.
Signed-off-by: Shawn O. Pearce <spearce@spearce.org> --- git-merge.sh | 39 ++++++++++++++++++++++----------------- 1 files changed, 22 insertions(+), 17 deletions(-)
diff --git a/git-merge.sh b/git-merge.sh index a8f673e..74d4fb0 100755 --- a/git-merge.sh +++ b/git-merge.sh @@ -341,23 +341,28 @@ f,*) ?,1,*,) # We are not doing octopus, not fast forward, and have only # one common. See if it is really trivial. - git var GIT_COMMITTER_IDENT >/dev/null || exit - - echo "Trying really trivial in-index merge..." - git-update-index --refresh 2>/dev/null - if git-read-tree --trivial -m -u -v $common $head "$1" && - result_tree=$(git-write-tree) - then - echo "Wonderful." - result_commit=$( - echo "$merge_msg" | - git-commit-tree $result_tree -p HEAD -p "$1" - ) || exit - finish "$result_commit" "In-index merge" - dropsave - exit 0 - fi - echo "Nope." + case "$use_strategies" in + recursive|'recursive '|recur|'recur ') + : run merge later + ;; + *) + git var GIT_COMMITTER_IDENT >/dev/null || exit + echo "Trying really trivial in-index merge..." + git-update-index --refresh 2>/dev/null + if git-read-tree --trivial -m -u -v $common $head "$1" && + result_tree=$(git-write-tree) + then + echo "Wonderful." + result_commit=$( + echo "$merge_msg" | + git-commit-tree $result_tree -p HEAD -p "$1" + ) || exit + finish "$result_commit" "In-index merge" + dropsave + exit 0 + fi + echo "Nope." + esac ;; *) # An octopus. If we can reach all the remote we are up to date.
-- 1.4.4.3.gd2e4