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"
$ hg init master
$ cd master
$ cat >> .hg/hgrc <<EOF
> [remotefilelog]
> server=True
> EOF
$ echo x > x
$ hg commit -qAm x
$ echo y >> x
$ hg commit -qAm y
$ echo z >> x
$ hg commit -qAm z
$ cd ..
$ hgcloneshallow ssh://user@dummy/master shallow -q
1 files fetched over 1 fetches - (1 misses, 0.00% hit ratio) over *s (glob)
$ cd shallow
Unbundling a shallow bundle
$ hg strip -r 66ee28d0328c
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
saved backup bundle to $TESTTMP/shallow/.hg/strip-backup/66ee28d0328c-3d7aafd1-backup.hg (glob)
2 files fetched over 2 fetches - (2 misses, 0.00% hit ratio) over *s (glob)
$ hg unbundle .hg/strip-backup/66ee28d0328c-3d7aafd1-backup.hg
adding changesets
adding manifests
adding file changes
added 2 changesets with 2 changes to 1 files
new changesets 66ee28d0328c:16db62c5946f
(run 'hg update' to get a working copy)
Unbundling a full bundle
$ hg -R ../master bundle -r 66ee28d0328c:: --base "66ee28d0328c^" ../fullbundle.hg
2 changesets found
$ hg strip -r 66ee28d0328c
saved backup bundle to $TESTTMP/shallow/.hg/strip-backup/66ee28d0328c-3d7aafd1-backup.hg (glob)
$ hg unbundle ../fullbundle.hg
adding changesets
adding manifests
adding file changes
added 2 changesets with 2 changes to 1 files
new changesets 66ee28d0328c:16db62c5946f (2 drafts)
(run 'hg update' to get a working copy)
Pulling from a shallow bundle
$ hg strip -r 66ee28d0328c --config remotefilelog.strip.includefiles=none
saved backup bundle to $TESTTMP/shallow/.hg/strip-backup/66ee28d0328c-3d7aafd1-backup.hg (glob)
$ hg pull -r 66ee28d0328c .hg/strip-backup/66ee28d0328c-3d7aafd1-backup.hg
pulling from .hg/strip-backup/66ee28d0328c-3d7aafd1-backup.hg
searching for changes
adding changesets
adding manifests
adding file changes
added 1 changesets with 0 changes to 0 files
new changesets 66ee28d0328c (1 drafts)
(run 'hg update' to get a working copy)
Pulling from a full bundle, also testing that strip produces a full bundle by
default.
$ hg strip -r 66ee28d0328c
saved backup bundle to $TESTTMP/shallow/.hg/strip-backup/66ee28d0328c-b6ee89e7-backup.hg (glob)
$ hg pull -r 66ee28d0328c .hg/strip-backup/66ee28d0328c-b6ee89e7-backup.hg
pulling from .hg/strip-backup/66ee28d0328c-b6ee89e7-backup.hg
searching for changes
abort: cannot pull from full bundles
(use `hg unbundle` instead)
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