largefiles: optimize update speed by only updating changed largefiles
Historically, during 'hg update', every largefile in the working copy was
hashed (which is a very expensive operation on big files) and any
largefiles that did not have a hash that matched their standin were
updated.
This patch optimizes 'hg update' by keeping track of what standins have
changed between the old and new revisions, and only updating the largefiles
that have changed. This saves a lot of time by avoiding the unecessary
calculation of a list of sha1 hashes for big files.
With this patch, the time 'hg update' takes to complete is a function of
how many largefiles need to be updated and what their size is.
Performance tests on a repository with about 80 largefiles ranging from
a few MB to about 97 MB are shown below. The tests show how long it takes
to run 'hg update' with no changes actually being updated.
Mercurial 2.1 release:
$ time hg update
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
getting changed largefiles
0 largefiles updated, 0 removed
real 0m10.045s
user 0m9.367s
sys 0m0.674s
With this patch:
$ time hg update
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
real 0m0.965s
user 0m0.845s
sys 0m0.115s
The same repsoitory, without the largefiles extension enabled:
$ time hg update
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
real 0m0.799s
user 0m0.684s
sys 0m0.111s
So before the patch, 'hg update' with no changes was approximately 9.25s
slower with largefiles enabled. With this patch, it is approximately 0.165s
slower.
Test for changeset 9fe267f77f56ff127cf7e65dc15dd9de71ce8ceb
(merge correctly when all the files in a directory are moved
but then local changes are added in the same directory)
$ hg init a
$ cd a
$ mkdir -p testdir
$ echo a > testdir/a
$ hg add testdir/a
$ hg commit -m a
$ cd ..
$ hg clone a b
updating to branch default
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ cd a
$ echo alpha > testdir/a
$ hg commit -m remote-change
$ cd ..
$ cd b
$ mkdir testdir/subdir
$ hg mv testdir/a testdir/subdir/a
$ hg commit -m move
$ mkdir newdir
$ echo beta > newdir/beta
$ hg add newdir/beta
$ hg commit -m local-addition
$ hg pull ../a
pulling from ../a
searching for changes
adding changesets
adding manifests
adding file changes
added 1 changesets with 1 changes to 1 files (+1 heads)
(run 'hg heads' to see heads, 'hg merge' to merge)
$ hg up -C 2
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg merge
merging testdir/subdir/a and testdir/a to testdir/subdir/a
0 files updated, 1 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
$ hg stat
M testdir/subdir/a
$ hg diff --nodates
diff -r bc21c9773bfa testdir/subdir/a
--- a/testdir/subdir/a
+++ b/testdir/subdir/a
@@ -1,1 +1,1 @@
-a
+alpha