store: implement fncache basic path encoding in C
(This is not yet enabled; it will be turned on in a followup patch.)
The path encoding performed by fncache is complex and (perhaps
surprisingly) slow enough to negatively affect the overall performance
of Mercurial.
For a short path (< 120 bytes), the Python code can be reduced to a fairly
tractable state machine that either determines that nothing needs to be
done in a single pass, or performs the encoding in a second pass.
For longer paths, we avoid the more complicated hashed encoding scheme
for now, and fall back to Python.
Raw performance: I measured in a repo containing 150,000 files in its tip
manifest, with a median path name length of 57 bytes, and 95th percentile
of 96 bytes.
In this repo, the Python code takes 3.1 seconds to encode all path
names, while the hybrid C-and-Python code (called from Python) takes
0.21 seconds, for a speedup of about 14.
Across several other large repositories, I've measured the speedup from
the C code at between 26x and 40x.
For path names above 120 bytes where we must fall back to Python for
hashed encoding, the speedup is about 1.7x. Thus absolute performance
will depend strongly on the characteristics of a particular repository.
$ echo "[extensions]" >> $HGRCPATH
$ echo "mq=" >> $HGRCPATH
$ tipparents() {
> hg parents --template "{rev}:{node|short} {desc|firstline}\n" -r tip
> }
Test import and merge diffs
$ hg init repo
$ cd repo
$ echo a > a
$ hg ci -Am adda
adding a
$ echo a >> a
$ hg ci -m changea
$ echo c > c
$ hg ci -Am addc
adding c
$ hg up 0
1 files updated, 0 files merged, 1 files removed, 0 files unresolved
$ echo b > b
$ hg ci -Am addb
adding b
created new head
$ hg up 1
1 files updated, 0 files merged, 1 files removed, 0 files unresolved
$ hg merge 3
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
$ hg ci -m merge
$ hg export . > ../merge.diff
$ cd ..
$ hg clone -r2 repo repo2
adding changesets
adding manifests
adding file changes
added 3 changesets with 3 changes to 2 files
updating to branch default
2 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ cd repo2
$ hg pull -r3 ../repo
pulling from ../repo
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)
Test without --exact and diff.p1 == workingdir.p1
$ hg up 1
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
$ hg import ../merge.diff
applying ../merge.diff
$ tipparents
1:540395c44225 changea
3:102a90ea7b4a addb
$ hg strip --no-backup tip
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
Test without --exact and diff.p1 != workingdir.p1
$ hg up 2
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg import ../merge.diff
applying ../merge.diff
$ tipparents
2:890ecaa90481 addc
$ hg strip --no-backup tip
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
Test with --exact
$ hg import --exact ../merge.diff
applying ../merge.diff
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
$ tipparents
1:540395c44225 changea
3:102a90ea7b4a addb
$ hg strip --no-backup tip
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
Test with --bypass and diff.p1 == workingdir.p1
$ hg up 1
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg import --bypass ../merge.diff
applying ../merge.diff
$ tipparents
1:540395c44225 changea
3:102a90ea7b4a addb
$ hg strip --no-backup tip
Test with --bypass and diff.p1 != workingdir.p1
$ hg up 2
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg import --bypass ../merge.diff
applying ../merge.diff
$ tipparents
2:890ecaa90481 addc
$ hg strip --no-backup tip
Test with --bypass and --exact
$ hg import --bypass --exact ../merge.diff
applying ../merge.diff
$ tipparents
1:540395c44225 changea
3:102a90ea7b4a addb
$ hg strip --no-backup tip
$ cd ..