bisect: avoid copying ancestor list for non-merge commits
During a bisection, hg needs to compute a list of all ancestors for every
candidate commit. This is accomplished via a bottom-up traversal of the set of
candidates, during which each revision's ancestor list is populated using the
ancestor list of its parent(s). Previously, this involved copying the entire
list, which could be very long in if the bisection range was large.
To help improve this, we can observe that each candidate commit is visited
exactly once, at which point its ancestor list is copied into its children's
lists and then dropped. In the case of non-merge commits, a commit's ancestor
list consists exactly of its parent's list plus itself. This means that we can
trivially reuse the parent's existing list for one of its non-merge children,
which avoids copying entirely if that commit is the parent's only child. This
makes bisections over linear ranges of commits much faster.
During some informal testing in the large publicly-available `mozilla-central`
repository, this noticeably sped up bisections over large ranges of history:
Setup:
$ cd mozilla-central
$ hg bisect --reset
$ hg bisect --good 0
$ hg log -r tip -T '{rev}\n'
628417
Test:
$ time hg bisect --bad tip --noupdate
Before:
real 3m35.927s
user 3m35.553s
sys 0m0.319s
After:
real 1m41.142s
user 1m40.810s
sys 0m0.285s
#require no-windows
$ . "$TESTDIR/remotefilelog-library.sh"
generaldelta to generaldelta interactions with bundle2 but legacy clients
without changegroup2 support
$ cat > testcg2.py << EOF
> import sys
> from mercurial import changegroup, registrar, util
> cmdtable = {}
> command = registrar.command(cmdtable)
> @command('testcg2', norepo=True)
> def testcg2(ui):
> if not util.safehasattr(changegroup, 'cg2packer'):
> sys.exit(80)
> EOF
$ cat >> $HGRCPATH << EOF
> [extensions]
> testcg2 = $TESTTMP/testcg2.py
> EOF
$ hg testcg2 || exit 80
$ cat > disablecg2.py << EOF
> from mercurial import changegroup, error, util
> deleted = False
> def reposetup(ui, repo):
> global deleted
> if deleted:
> return
> packermap = changegroup._packermap
> # protect against future changes
> if len(packermap) != 3:
> raise error.Abort('packermap has %d versions, expected 3!' % len(packermap))
> for k in ['01', '02', '03']:
> if not packermap.get(k):
> raise error.Abort("packermap doesn't have key '%s'!" % k)
>
> del packermap['02']
> deleted = True
> EOF
$ hg init master
$ hg debugrequires -R master | grep generaldelta
generaldelta
$ cd master
preferuncompressed = False so that we can make both generaldelta and non-generaldelta clones
$ cat >> .hg/hgrc <<EOF
> [remotefilelog]
> server=True
> [experimental]
> bundle2-exp = True
> [server]
> preferuncompressed = False
> EOF
$ echo x > x
$ hg commit -qAm x
$ cd ..
$ hgcloneshallow ssh://user@dummy/master shallow -q --pull --config experimental.bundle2-exp=True
1 files fetched over 1 fetches - (1 misses, 0.00% hit ratio) over *s (glob)
$ cd shallow
$ cat >> .hg/hgrc << EOF
> [extensions]
> disablecg2 = $TESTTMP/disablecg2.py
> EOF
$ cd ../master
$ echo y > y
$ hg commit -qAm y
$ cd ../shallow
$ hg pull -u
pulling from ssh://user@dummy/master
searching for changes
adding changesets
adding manifests
adding file changes
added 1 changesets with 0 changes to 0 files
new changesets d34c38483be9
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
1 files fetched over 1 fetches - (1 misses, 0.00% hit ratio) over *s (glob)
$ echo a > a
$ hg commit -qAm a
$ hg push
pushing to ssh://user@dummy/master
searching for changes
remote: adding changesets
remote: adding manifests
remote: adding file changes
remote: added 1 changesets with 1 changes to 1 files