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.
$ . "$TESTDIR/narrow-library.sh"
$ hg init master
$ cd master
$ mkdir inside
$ echo inside > inside/f1
$ mkdir outside
$ echo outside > outside/f2
$ mkdir patchdir
$ echo patch_this > patchdir/f3
$ hg ci -Aqm 'initial'
$ cd ..
$ hg clone --narrow ssh://user@dummy/master narrow --include inside
requesting all changes
adding changesets
adding manifests
adding file changes
added 1 changesets with 1 changes to 1 files
new changesets dff6a2a6d433
updating to branch default
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ cd narrow
$ mkdir outside
$ echo other_contents > outside/f2
$ grep outside .hg/narrowspec
[1]
$ grep outside .hg/dirstate
[1]
$ hg status
`hg status` did not add outside.
$ grep outside .hg/narrowspec
[1]
$ grep outside .hg/dirstate
[1]
Unfortunately this is not really a candidate for adding to narrowhg proper,
since it depends on some other source for providing the manifests (when using
treemanifests) and file contents. Something like a virtual filesystem and/or
remotefilelog. We want to be useful when not using those systems, so we do not
have this method available in narrowhg proper at the moment.
$ cat > "$TESTTMP/expand_extension.py" <<EOF
> import os
> import sys
>
> from mercurial import encoding
> from mercurial import extensions
> from mercurial import localrepo
> from mercurial import match as matchmod
> from mercurial import narrowspec
> from mercurial import patch
> from mercurial import util as hgutil
>
> def expandnarrowspec(ui, repo, newincludes=None):
> if not newincludes:
> return
> import sys
> newincludes = set([newincludes])
> includes, excludes = repo.narrowpats
> currentmatcher = narrowspec.match(repo.root, includes, excludes)
> includes = includes | newincludes
> if not repo.currenttransaction():
> ui.develwarn(b'expandnarrowspec called outside of transaction!')
> repo.setnarrowpats(includes, excludes)
> newmatcher = narrowspec.match(repo.root, includes, excludes)
> added = matchmod.differencematcher(newmatcher, currentmatcher)
> for f in repo[b'.'].manifest().walk(added):
> repo.dirstate.normallookup(f)
>
> def wrapds(ui, repo, ds):
> class expandingdirstate(ds.__class__):
> @hgutil.propertycache
> def _map(self):
> ret = super(expandingdirstate, self)._map
> with repo.wlock(), repo.lock(), repo.transaction(
> b'expandnarrowspec'):
> expandnarrowspec(ui, repo,
> encoding.environ.get(b'DIRSTATEINCLUDES'))
> return ret
> ds.__class__ = expandingdirstate
> return ds
>
> def reposetup(ui, repo):
> class expandingrepo(repo.__class__):
> def _makedirstate(self):
> dirstate = super(expandingrepo, self)._makedirstate()
> return wrapds(ui, repo, dirstate)
> repo.__class__ = expandingrepo
>
> def extsetup(unused_ui):
> def overridepatch(orig, ui, repo, *args, **kwargs):
> with repo.wlock():
> expandnarrowspec(ui, repo, encoding.environ.get(b'PATCHINCLUDES'))
> return orig(ui, repo, *args, **kwargs)
>
> extensions.wrapfunction(patch, b'patch', overridepatch)
> EOF
$ cat >> ".hg/hgrc" <<EOF
> [extensions]
> expand_extension = $TESTTMP/expand_extension.py
> EOF
Since we do not have the ability to rely on a virtual filesystem or
remotefilelog in the test, we just fake it by copying the data from the 'master'
repo.
$ cp -a ../master/.hg/store/data/* .hg/store/data
Do that for patchdir as well.
$ cp -a ../master/patchdir .
`hg status` will now add outside, but not patchdir.
$ DIRSTATEINCLUDES=path:outside hg status
M outside/f2
$ grep outside .hg/narrowspec
path:outside
$ grep outside .hg/dirstate > /dev/null
$ grep patchdir .hg/narrowspec
[1]
$ grep patchdir .hg/dirstate
[1]
Get rid of the modification to outside/f2.
$ hg update -C .
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
This patch will not apply cleanly at the moment, so `hg import` will break
$ cat > "$TESTTMP/foo.patch" <<EOF
> --- patchdir/f3
> +++ patchdir/f3
> @@ -1,1 +1,1 @@
> -this should be "patch_this", but its not, so patch fails
> +this text is irrelevant
> EOF
$ PATCHINCLUDES=path:patchdir hg import -p0 -e "$TESTTMP/foo.patch" -m ignored
applying $TESTTMP/foo.patch
patching file patchdir/f3
Hunk #1 FAILED at 0
1 out of 1 hunks FAILED -- saving rejects to file patchdir/f3.rej
abort: patch failed to apply
[255]
$ grep patchdir .hg/narrowspec
[1]
$ grep patchdir .hg/dirstate > /dev/null
[1]
Let's make it apply cleanly and see that it *did* expand properly
$ cat > "$TESTTMP/foo.patch" <<EOF
> --- patchdir/f3
> +++ patchdir/f3
> @@ -1,1 +1,1 @@
> -patch_this
> +patched_this
> EOF
$ PATCHINCLUDES=path:patchdir hg import -p0 -e "$TESTTMP/foo.patch" -m message
applying $TESTTMP/foo.patch
$ cat patchdir/f3
patched_this
$ grep patchdir .hg/narrowspec
path:patchdir
$ grep patchdir .hg/dirstate > /dev/null