changegroup: store old heads as a set
Previously, the "oldheads" variable was a list. On a repository at
Mozilla with 46,492 heads, profiling revealed that list membership
testing was dominating execution time of applying small changegroups.
This patch converts the list of old heads to a set. This makes
membership testing significantly faster. On the aforementioned
repository with 46,492 heads:
$ hg unbundle <file with 1 changeset>
before: 18.535s wall
after: 1.303s
Consumers of this variable only check for truthiness (`if oldheads`),
length (`len(oldheads)`), and (most importantly) item membership
(`h not in oldheads` - which occurs twice). So, the change to a set
should be safe and suitable for stable.
The practical effect of this change is that changegroup application
and related operations (like `hg push`) no longer exhibit an O(n^2)
CPU explosion as the number of heads grows.
$ cat > echo.py <<EOF
> #!/usr/bin/env python
> import os, sys
> try:
> import msvcrt
> msvcrt.setmode(sys.stdout.fileno(), os.O_BINARY)
> msvcrt.setmode(sys.stderr.fileno(), os.O_BINARY)
> except ImportError:
> pass
>
> for k in ('HG_FILE', 'HG_MY_ISLINK', 'HG_OTHER_ISLINK', 'HG_BASE_ISLINK'):
> print k, os.environ[k]
> EOF
Create 2 heads containing the same file, once as
a file, once as a link. Bundle was generated with:
# hg init t
# cd t
# echo a > a
# hg ci -qAm t0 -d '0 0'
# echo l > l
# hg ci -qAm t1 -d '1 0'
# hg up -C 0
# ln -s a l
# hg ci -qAm t2 -d '2 0'
# echo l2 > l2
# hg ci -qAm t3 -d '3 0'
$ hg init t
$ cd t
$ hg -q pull "$TESTDIR/bundles/test-merge-symlinks.hg"
$ hg up -C 3
3 files updated, 0 files merged, 0 files removed, 0 files unresolved
Merge them and display *_ISLINK vars
merge heads
$ hg merge --tool="python ../echo.py"
merging l
HG_FILE l
HG_MY_ISLINK 1
HG_OTHER_ISLINK 0
HG_BASE_ISLINK 0
0 files updated, 1 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
Test working directory symlink bit calculation wrt copies,
especially on non-supporting systems.
merge working directory
$ hg up -C 2
1 files updated, 0 files merged, 1 files removed, 0 files unresolved
$ hg copy l l2
$ HGMERGE="python ../echo.py" hg up 3
merging l2
HG_FILE l2
HG_MY_ISLINK 1
HG_OTHER_ISLINK 0
HG_BASE_ISLINK 0
0 files updated, 1 files merged, 0 files removed, 0 files unresolved
$ cd ..