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.
setup repo
$ hg init t
$ cd t
$ echo a > a
$ hg commit -Am'add a'
adding a
$ hg verify
checking changesets
checking manifests
crosschecking files in changesets and manifests
checking files
1 files, 1 changesets, 1 total revisions
$ hg parents
changeset: 0:1f0dee641bb7
tag: tip
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: add a
rollback to null revision
$ hg status
$ hg rollback
repository tip rolled back to revision -1 (undo commit)
working directory now based on revision -1
$ hg verify
checking changesets
checking manifests
crosschecking files in changesets and manifests
checking files
0 files, 0 changesets, 0 total revisions
$ hg parents
$ hg status
A a
Two changesets this time so we rollback to a real changeset
$ hg commit -m'add a again'
$ echo a >> a
$ hg commit -m'modify a'
Test issue 902 (current branch is preserved)
$ hg branch test
marked working directory as branch test
(branches are permanent and global, did you want a bookmark?)
$ hg rollback
repository tip rolled back to revision 0 (undo commit)
working directory now based on revision 0
$ hg branch
default
Test issue 1635 (commit message saved)
$ cat .hg/last-message.txt ; echo
modify a
Test rollback of hg before issue 902 was fixed
$ hg commit -m "test3"
$ hg branch test
marked working directory as branch test
(branches are permanent and global, did you want a bookmark?)
$ rm .hg/undo.branch
$ hg rollback
repository tip rolled back to revision 0 (undo commit)
named branch could not be reset: current branch is still 'test'
working directory now based on revision 0
$ hg branch
test
working dir unaffected by rollback: do not restore dirstate et. al.
$ hg log --template '{rev} {branch} {desc|firstline}\n'
0 default add a again
$ hg status
M a
$ hg bookmark foo
$ hg commit -m'modify a again'
$ echo b > b
$ hg commit -Am'add b'
adding b
$ hg log --template '{rev} {branch} {desc|firstline}\n'
2 test add b
1 test modify a again
0 default add a again
$ hg update default
1 files updated, 0 files merged, 1 files removed, 0 files unresolved
$ hg bookmark bar
$ cat .hg/undo.branch ; echo
test
$ hg rollback -f
repository tip rolled back to revision 1 (undo commit)
$ hg id -n
0
$ hg branch
default
$ cat .hg/bookmarks.current ; echo
bar
$ hg bookmark --delete foo
rollback by pretxncommit saves commit message (issue 1635)
$ echo a >> a
$ hg --config hooks.pretxncommit=false commit -m"precious commit message"
transaction abort!
rollback completed
abort: pretxncommit hook exited with status * (glob)
[255]
$ cat .hg/last-message.txt ; echo
precious commit message
same thing, but run $EDITOR
$ cat > editor.sh << '__EOF__'
> echo "another precious commit message" > "$1"
> __EOF__
$ HGEDITOR="\"sh\" \"`pwd`/editor.sh\"" hg --config hooks.pretxncommit=false commit 2>&1
transaction abort!
rollback completed
note: commit message saved in .hg/last-message.txt
abort: pretxncommit hook exited with status * (glob)
[255]
$ cat .hg/last-message.txt
another precious commit message
test rollback on served repository
#if serve
$ hg commit -m "precious commit message"
$ hg serve -p $HGPORT -d --pid-file=hg.pid -A access.log -E errors.log
$ cat hg.pid >> $DAEMON_PIDS
$ cd ..
$ hg clone http://localhost:$HGPORT u
requesting all changes
adding changesets
adding manifests
adding file changes
added 3 changesets with 2 changes to 1 files (+1 heads)
updating to branch default
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ cd u
$ hg id default
068774709090
now rollback and observe that 'hg serve' reloads the repository and
presents the correct tip changeset:
$ hg -R ../t rollback
repository tip rolled back to revision 1 (undo commit)
working directory now based on revision 0
$ hg id default
791dd2169706
#endif
update to older changeset and then refuse rollback, because
that would lose data (issue2998)
$ cd ../t
$ hg -q update
$ rm `hg status -un`
$ template='{rev}:{node|short} [{branch}] {desc|firstline}\n'
$ echo 'valuable new file' > b
$ echo 'valuable modification' >> a
$ hg commit -A -m'a valuable change'
adding b
$ hg update 0
1 files updated, 0 files merged, 1 files removed, 0 files unresolved
$ hg rollback
abort: rollback of last commit while not checked out may lose data
(use -f to force)
[255]
$ hg tip -q
2:4d9cd3795eea
$ hg rollback -f
repository tip rolled back to revision 1 (undo commit)
$ hg status
$ hg log --removed b # yep, it's gone
same again, but emulate an old client that doesn't write undo.desc
$ hg -q update
$ echo 'valuable modification redux' >> a
$ hg commit -m'a valuable change redux'
$ rm .hg/undo.desc
$ hg update 0
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg rollback
rolling back unknown transaction
$ cat a
a
$ cd ..