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 "graphlog=" >> $HGRCPATH
plain
$ hg init
$ hg debugbuilddag '+2:f +3:p2 @temp <f+4 @default /p2 +2' \
> --config extensions.progress= --config progress.assume-tty=1 \
> --config progress.delay=0 --config progress.refresh=0 \
> --config progress.format=topic,bar,number \
> --config progress.width=60 2>&1 | \
> python "$TESTDIR/filtercr.py"
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building [=====================================> ] 11/12
building [=====================================> ] 11/12
\r (esc)
tags
$ cat .hg/localtags
66f7d451a68b85ed82ff5fcc254daf50c74144bd f
bebd167eb94d257ace0e814aeb98e6972ed2970d p2
dag
$ hg debugdag -t -b
+2:f
+3:p2
@temp*f+3
@default*/p2+2:tip
tip
$ hg id
000000000000
glog
$ hg glog --template '{rev}: {desc} [{branches}] @ {date}\n'
o 11: r11 [] @ 11.00
|
o 10: r10 [] @ 10.00
|
o 9: r9 [] @ 9.00
|\
| o 8: r8 [temp] @ 8.00
| |
| o 7: r7 [temp] @ 7.00
| |
| o 6: r6 [temp] @ 6.00
| |
| o 5: r5 [temp] @ 5.00
| |
o | 4: r4 [] @ 4.00
| |
o | 3: r3 [] @ 3.00
| |
o | 2: r2 [] @ 2.00
|/
o 1: r1 [] @ 1.00
|
o 0: r0 [] @ 0.00
overwritten files, starting on a non-default branch
$ rm -r .hg
$ hg init
$ hg debugbuilddag '@start.@default.:f +3:p2 @temp <f+4 @default /p2 +2' -q -o
tags
$ cat .hg/localtags
f778700ebd50fcf282b23a4446bd155da6453eb6 f
bbccf169769006e2490efd2a02f11c3d38d462bd p2
dag
$ hg debugdag -t -b
@start+1
@default+1:f
+3:p2
@temp*f+3
@default*/p2+2:tip
tip
$ hg id
000000000000
glog
$ hg glog --template '{rev}: {desc} [{branches}] @ {date}\n'
o 11: r11 [] @ 11.00
|
o 10: r10 [] @ 10.00
|
o 9: r9 [] @ 9.00
|\
| o 8: r8 [temp] @ 8.00
| |
| o 7: r7 [temp] @ 7.00
| |
| o 6: r6 [temp] @ 6.00
| |
| o 5: r5 [temp] @ 5.00
| |
o | 4: r4 [] @ 4.00
| |
o | 3: r3 [] @ 3.00
| |
o | 2: r2 [] @ 2.00
|/
o 1: r1 [] @ 1.00
|
o 0: r0 [start] @ 0.00
glog of
$ hg glog --template '{rev}: {desc} [{branches}]\n' of
o 11: r11 []
|
o 10: r10 []
|
o 9: r9 []
|\
| o 8: r8 [temp]
| |
| o 7: r7 [temp]
| |
| o 6: r6 [temp]
| |
| o 5: r5 [temp]
| |
o | 4: r4 []
| |
o | 3: r3 []
| |
o | 2: r2 []
|/
o 1: r1 []
|
o 0: r0 [start]
tags
$ hg tags -v
tip 11:9ffe238a67a2
p2 4:bbccf1697690 local
f 1:f778700ebd50 local
cat of
$ hg cat of --rev tip
r11
new and mergeable files
$ rm -r .hg
$ hg init
$ hg debugbuilddag '+2:f +3:p2 @temp <f+4 @default /p2 +2' -q -mn
dag
$ hg debugdag -t -b
+2:f
+3:p2
@temp*f+3
@default*/p2+2:tip
tip
$ hg id
000000000000
glog
$ hg glog --template '{rev}: {desc} [{branches}] @ {date}\n'
o 11: r11 [] @ 11.00
|
o 10: r10 [] @ 10.00
|
o 9: r9 [] @ 9.00
|\
| o 8: r8 [temp] @ 8.00
| |
| o 7: r7 [temp] @ 7.00
| |
| o 6: r6 [temp] @ 6.00
| |
| o 5: r5 [temp] @ 5.00
| |
o | 4: r4 [] @ 4.00
| |
o | 3: r3 [] @ 3.00
| |
o | 2: r2 [] @ 2.00
|/
o 1: r1 [] @ 1.00
|
o 0: r0 [] @ 0.00
glog mf
$ hg glog --template '{rev}: {desc} [{branches}]\n' mf
o 11: r11 []
|
o 10: r10 []
|
o 9: r9 []
|\
| o 8: r8 [temp]
| |
| o 7: r7 [temp]
| |
| o 6: r6 [temp]
| |
| o 5: r5 [temp]
| |
o | 4: r4 []
| |
o | 3: r3 []
| |
o | 2: r2 []
|/
o 1: r1 []
|
o 0: r0 []
man r4
$ hg manifest -r4
mf
nf0
nf1
nf2
nf3
nf4
cat r4 mf
$ hg cat -r4 mf
0 r0
1
2 r1
3
4 r2
5
6 r3
7
8 r4
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
man r8
$ hg manifest -r8
mf
nf0
nf1
nf5
nf6
nf7
nf8
cat r8 mf
$ hg cat -r8 mf
0 r0
1
2 r1
3
4
5
6
7
8
9
10 r5
11
12 r6
13
14 r7
15
16 r8
17
18
19
20
21
22
23
man
$ hg manifest --rev tip
mf
nf0
nf1
nf10
nf11
nf2
nf3
nf4
nf5
nf6
nf7
nf8
nf9
cat mf
$ hg cat mf --rev tip
0 r0
1
2 r1
3
4 r2
5
6 r3
7
8 r4
9
10 r5
11
12 r6
13
14 r7
15
16 r8
17
18 r9
19
20 r10
21
22 r11
23