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.
$ hg init repo
$ cd repo
$ echo foo > foo
$ hg ci -qAm 'add foo'
$ echo >> foo
$ hg ci -m 'change foo'
$ hg up -qC 0
$ echo bar > bar
$ hg ci -qAm 'add bar'
$ hg log
changeset: 2:effea6de0384
tag: tip
parent: 0:bbd179dfa0a7
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: add bar
changeset: 1:ed1b79f46b9a
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: change foo
changeset: 0:bbd179dfa0a7
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: add foo
$ cd ..
don't show "(+1 heads)" message when pulling closed head
$ hg clone -q repo repo2
$ hg clone -q repo2 repo3
$ cd repo2
$ hg up -q 0
$ echo hello >> foo
$ hg ci -mx1
created new head
$ hg ci -mx2 --close-branch
$ cd ../repo3
$ hg heads -q --closed
2:effea6de0384
1:ed1b79f46b9a
$ hg pull
pulling from $TESTTMP/repo2 (glob)
searching for changes
adding changesets
adding manifests
adding file changes
added 2 changesets with 1 changes to 1 files
(run 'hg update' to get a working copy)
$ hg heads -q --closed
4:00cfe9073916
2:effea6de0384
1:ed1b79f46b9a
$ cd ..
$ hg init copy
$ cd copy
Pull a missing revision:
$ hg pull -qr missing ../repo
abort: unknown revision 'missing'!
[255]
Pull multiple revisions with update:
$ hg pull -qu -r 0 -r 1 ../repo
$ hg -q parents
0:bbd179dfa0a7
$ hg rollback
repository tip rolled back to revision -1 (undo pull)
working directory now based on revision -1
$ hg pull -qr 0 ../repo
$ hg log
changeset: 0:bbd179dfa0a7
tag: tip
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: add foo
$ hg pull -qr 1 ../repo
$ hg log
changeset: 1:ed1b79f46b9a
tag: tip
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: change foo
changeset: 0:bbd179dfa0a7
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: add foo
This used to abort: received changelog group is empty:
$ hg pull -qr 1 ../repo
$ cd ..