sparse-revlog: implement algorithm to write sparse delta chains (
issue5480)
The classic behavior of revlog._isgooddeltainfo is to consider the span size
of the whole delta chain, and limit it to 4 * textlen.
Once sparse-revlog writing is allowed (and enforced with a requirement),
revlog._isgooddeltainfo considers the span of the largest chunk as the
distance used in the verification, instead of using the span of the whole
delta chain.
In order to compute the span of the largest chunk, we need to slice into
chunks a chain with the new revision at the top of the revlog, and take the
maximal span of these chunks. The sparse read density is a parameter to the
slicing, as it will stop when the global read density reaches this threshold.
For instance, a density of 50% means that 2 of 4 read bytes are actually used
for the reconstruction of the revision (the others are part of other chains).
This allows a new revision to be potentially stored with a diff against
another revision anywhere in the history, instead of forcing it in the last 4
* textlen. The result is a much better compression on repositories that have
many concurrent branches. Here are a comparison between using deltas from
current upstream (aggressive-merge-deltas on by default) and deltas from a
sparse-revlog
Comparison of `.hg/store/` size:
mercurial (6.74% merges):
before: 46,831,873 bytes
after: 46,795,992 bytes (no relevant change)
pypy (8.30% merges):
before: 333,524,651 bytes
after: 308,417,511 bytes -8%
netbeans (34.21% merges):
before: 1,141,847,554 bytes
after: 1,131,093,161 bytes -1%
mozilla-central (4.84% merges):
before: 2,344,248,850 bytes
after: 2,328,459,258 bytes -1%
large-private-repo-A (merge 19.73%)
before: 41,510,550,163 bytes
after: 8,121,763,428 bytes -80%
large-private-repo-B (23.77%)
before: 58,702,221,709 bytes
after: 8,351,588,828 bytes -76%
Comparison of `00manifest.d` size:
mercurial (6.74% merges):
before: 6,143,044 bytes
after: 6,107,163 bytes
pypy (8.30% merges):
before: 52,941,780 bytes
after: 27,834,082 bytes -48%
netbeans (34.21% merges):
before: 130,088,982 bytes
after: 119,337,636 bytes -10%
mozilla-central (4.84% merges):
before: 215,096,339 bytes
after: 199,496,863 bytes -8%
large-private-repo-A (merge 19.73%)
before: 33,725,285,081 bytes
after: 390,302,545 bytes -99%
large-private-repo-B (23.77%)
before: 49,457,701,645 bytes
after: 1,366,752,187 bytes -97%
The better delta chains provide a performance boost in relevant repositories:
pypy, bundling 1000 revisions:
before: 1.670s
after: 1.149s -31%
Unbundling got a bit slower. probably because the sparse algorithm is still
pure
python.
pypy, unbundling 1000 revisions:
before: 4.062s
after: 4.507s +10%
Performance of bundle/unbundle in repository with few concurrent branches (eg:
mercurial) are unaffected.
No significant differences have been noticed then timing `hg push` and `hg
pull` locally. More state timings are being gathered.
Same as for aggressive-merge-delta, better delta comes with longer delta
chains. Longer chains have a performance impact. For example. The length of
the chain needed to get the manifest of pypy's tip moves from 82 item to 1929
items. This moves the restore time from 3.88ms to 11.3ms.
Delta chain length is an independent issue that affects repository without
this changes. It will be dealt with independently.
No significant differences have been observed on repositories where
`sparse-revlog` have not much effect (mercurial, unity, netbeans). On pypy,
small differences have been observed on some operation affected by delta chain
building and retrieval.
pypy, perfmanifest
before: 0.006162s
after: 0.017899s +190%
pypy, commit:
before: 0.382
after: 0.376 -1%
pypy, status:
before: 0.157
after: 0.168 +7%
More comprehensive and stable timing comparisons are in progress.
# Here we create a simple DAG which has just enough of the required
# topology to test all the bisection status labels:
#
# 13--14
# /
# 0--1--2--3---------9--10--11--12
# \ /
# 4--5--6--7--8
$ hg init
$ echo '0' >a
$ hg add a
$ hg ci -u test -d '0 0' -m '0'
$ echo '1' >a
$ hg ci -u test -d '1 0' -m '1'
branch 2-3
$ echo '2' >b
$ hg add b
$ hg ci -u test -d '2 0' -m '2'
$ echo '3' >b
$ hg ci -u test -d '3 0' -m '3'
branch 4-8
$ hg up -r 1
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
$ echo '4' >c
$ hg add c
$ hg ci -u test -d '4 0' -m '4'
created new head
$ echo '5' >c
$ hg ci -u test -d '5 0' -m '5'
$ echo '6' >c
$ hg ci -u test -d '6 0' -m '6'
$ echo '7' >c
$ hg ci -u test -d '7 0' -m '7'
$ echo '8' >c
$ hg ci -u test -d '8 0' -m '8'
merge
$ hg merge -r 3
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
$ hg ci -u test -d '9 0' -m '9=8+3'
$ echo '10' >a
$ hg ci -u test -d '10 0' -m '10'
$ echo '11' >a
$ hg ci -u test -d '11 0' -m '11'
$ echo '12' >a
$ hg ci -u test -d '12 0' -m '12'
unrelated branch
$ hg up -r 3
1 files updated, 0 files merged, 1 files removed, 0 files unresolved
$ echo '13' >d
$ hg add d
$ hg ci -u test -d '13 0' -m '13'
created new head
$ echo '14' >d
$ hg ci -u test -d '14 0' -m '14'
mark changesets
$ hg bisect --reset
$ hg bisect --good 4
$ hg bisect --good 6
$ hg bisect --bad 12
Testing changeset 9:2197c557e14c (6 changesets remaining, ~2 tests)
1 files updated, 0 files merged, 1 files removed, 0 files unresolved
$ hg bisect --bad 10
Testing changeset 8:e74a86251f58 (4 changesets remaining, ~2 tests)
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
$ hg bisect --skip 7
Testing changeset 8:e74a86251f58 (4 changesets remaining, ~2 tests)
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
test template
$ hg log --template '{rev}:{node|short} {bisect}\n'
14:cbf2f3105bbf
13:e07efca37c43
12:98c6b56349c0 bad
11:03f491376e63 bad (implicit)
10:c012b15e2409 bad
9:2197c557e14c untested
8:e74a86251f58 untested
7:a5f87041c899 skipped
6:7d997bedcd8d good
5:2dd1875f1028 good (implicit)
4:2a1daef14cd4 good
3:8417d459b90c ignored
2:e1355ee1f23e ignored
1:ce7c85e06a9f good (implicit)
0:b4e73ffab476 good (implicit)
$ hg log --template '{bisect|shortbisect} {rev}:{node|short}\n'
14:cbf2f3105bbf
13:e07efca37c43
B 12:98c6b56349c0
B 11:03f491376e63
B 10:c012b15e2409
U 9:2197c557e14c
U 8:e74a86251f58
S 7:a5f87041c899
G 6:7d997bedcd8d
G 5:2dd1875f1028
G 4:2a1daef14cd4
I 3:8417d459b90c
I 2:e1355ee1f23e
G 1:ce7c85e06a9f
G 0:b4e73ffab476
test style
$ hg log --style bisect
changeset: 14:cbf2f3105bbf
bisect:
tag: tip
user: test
date: Thu Jan 01 00:00:14 1970 +0000
summary: 14
changeset: 13:e07efca37c43
bisect:
parent: 3:8417d459b90c
user: test
date: Thu Jan 01 00:00:13 1970 +0000
summary: 13
changeset: 12:98c6b56349c0
bisect: bad
user: test
date: Thu Jan 01 00:00:12 1970 +0000
summary: 12
changeset: 11:03f491376e63
bisect: bad (implicit)
user: test
date: Thu Jan 01 00:00:11 1970 +0000
summary: 11
changeset: 10:c012b15e2409
bisect: bad
user: test
date: Thu Jan 01 00:00:10 1970 +0000
summary: 10
changeset: 9:2197c557e14c
bisect: untested
parent: 8:e74a86251f58
parent: 3:8417d459b90c
user: test
date: Thu Jan 01 00:00:09 1970 +0000
summary: 9=8+3
changeset: 8:e74a86251f58
bisect: untested
user: test
date: Thu Jan 01 00:00:08 1970 +0000
summary: 8
changeset: 7:a5f87041c899
bisect: skipped
user: test
date: Thu Jan 01 00:00:07 1970 +0000
summary: 7
changeset: 6:7d997bedcd8d
bisect: good
user: test
date: Thu Jan 01 00:00:06 1970 +0000
summary: 6
changeset: 5:2dd1875f1028
bisect: good (implicit)
user: test
date: Thu Jan 01 00:00:05 1970 +0000
summary: 5
changeset: 4:2a1daef14cd4
bisect: good
parent: 1:ce7c85e06a9f
user: test
date: Thu Jan 01 00:00:04 1970 +0000
summary: 4
changeset: 3:8417d459b90c
bisect: ignored
user: test
date: Thu Jan 01 00:00:03 1970 +0000
summary: 3
changeset: 2:e1355ee1f23e
bisect: ignored
user: test
date: Thu Jan 01 00:00:02 1970 +0000
summary: 2
changeset: 1:ce7c85e06a9f
bisect: good (implicit)
user: test
date: Thu Jan 01 00:00:01 1970 +0000
summary: 1
changeset: 0:b4e73ffab476
bisect: good (implicit)
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: 0
$ hg log --quiet --style bisect
14:cbf2f3105bbf
13:e07efca37c43
B 12:98c6b56349c0
B 11:03f491376e63
B 10:c012b15e2409
U 9:2197c557e14c
U 8:e74a86251f58
S 7:a5f87041c899
G 6:7d997bedcd8d
G 5:2dd1875f1028
G 4:2a1daef14cd4
I 3:8417d459b90c
I 2:e1355ee1f23e
G 1:ce7c85e06a9f
G 0:b4e73ffab476
$ hg --config extensions.color= --color=debug log --quiet --style bisect
[log.bisect| ] 14:cbf2f3105bbf
[log.bisect| ] 13:e07efca37c43
[log.bisect bisect.bad|B] 12:98c6b56349c0
[log.bisect bisect.bad|B] 11:03f491376e63
[log.bisect bisect.bad|B] 10:c012b15e2409
[log.bisect bisect.untested|U] 9:2197c557e14c
[log.bisect bisect.untested|U] 8:e74a86251f58
[log.bisect bisect.skipped|S] 7:a5f87041c899
[log.bisect bisect.good|G] 6:7d997bedcd8d
[log.bisect bisect.good|G] 5:2dd1875f1028
[log.bisect bisect.good|G] 4:2a1daef14cd4
[log.bisect bisect.ignored|I] 3:8417d459b90c
[log.bisect bisect.ignored|I] 2:e1355ee1f23e
[log.bisect bisect.good|G] 1:ce7c85e06a9f
[log.bisect bisect.good|G] 0:b4e73ffab476