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 sqlite no-chg
The sqlitestore backend leaves transactions around when used with chg.
Since this backend is primarily intended as proof-of-concept for
alternative storage backends, disable it for chg test runs to avoid
the instability.
$ cat >> $HGRCPATH <<EOF
> [extensions]
> sqlitestore =
> EOF
New repo should not use SQLite by default
$ hg init empty-no-sqlite
$ hg debugrequires -R empty-no-sqlite
dotencode
dirstate-v2 (dirstate-v2 !)
fncache
generaldelta
persistent-nodemap (rust !)
revlog-compression-zstd (zstd !)
revlogv1
share-safe
sparserevlog
store
storage.new-repo-backend=sqlite is recognized
$ hg --config storage.new-repo-backend=sqlite init empty-sqlite
$ hg debugrequires -R empty-sqlite
dotencode
dirstate-v2 (dirstate-v2 !)
exp-sqlite-001
exp-sqlite-comp-001=zstd (zstd !)
exp-sqlite-comp-001=$BUNDLE2_COMPRESSIONS$ (no-zstd !)
fncache
generaldelta
persistent-nodemap (rust !)
revlog-compression-zstd (zstd !)
revlogv1
share-safe
sparserevlog
store
$ cat >> $HGRCPATH << EOF
> [storage]
> new-repo-backend = sqlite
> EOF
Can force compression to zlib
$ hg --config storage.sqlite.compression=zlib init empty-zlib
$ hg debugrequires -R empty-zlib
dotencode
dirstate-v2 (dirstate-v2 !)
exp-sqlite-001
exp-sqlite-comp-001=$BUNDLE2_COMPRESSIONS$
fncache
generaldelta
persistent-nodemap (rust !)
revlog-compression-zstd (zstd !)
revlogv1
share-safe
sparserevlog
store
Can force compression to none
$ hg --config storage.sqlite.compression=none init empty-none
$ hg debugrequires -R empty-none
dotencode
dirstate-v2 (dirstate-v2 !)
exp-sqlite-001
exp-sqlite-comp-001=none
fncache
generaldelta
persistent-nodemap (rust !)
revlog-compression-zstd (zstd !)
revlogv1
share-safe
sparserevlog
store
Can make a local commit
$ hg init local-commit
$ cd local-commit
$ echo 0 > foo
$ hg commit -A -m initial
adding foo
That results in a row being inserted into various tables
$ sqlite3 .hg/store/db.sqlite -init /dev/null << EOF
> SELECT * FROM filepath;
> EOF
1|foo
$ sqlite3 .hg/store/db.sqlite -init /dev/null << EOF
> SELECT * FROM fileindex;
> EOF
1|1|0|-1|-1|0|0|1||6/\xef(L\xe2\xca\x02\xae\xcc\x8d\xe6\xd5\xe8\xa1\xc3\xaf\x05V\xfe (esc)
$ sqlite3 .hg/store/db.sqlite -init /dev/null << EOF
> SELECT * FROM delta;
> EOF
1|1| \xd2\xaf\x8d\xd2"\x01\xdd\x8dH\xe5\xdc\xfc\xae\xd2\x81\xff\x94"\xc7|0 (esc)
Tracking multiple files works
$ echo 1 > bar
$ hg commit -A -m 'add bar'
adding bar
$ sqlite3 .hg/store/db.sqlite -init /dev/null << EOF
> SELECT * FROM filedata ORDER BY id ASC;
> EOF
1|1|foo|0|6/\xef(L\xe2\xca\x02\xae\xcc\x8d\xe6\xd5\xe8\xa1\xc3\xaf\x05V\xfe|-1|-1|0|0|1| (esc)
2|2|bar|0|\xb8\xe0/d3s\x80!\xa0e\xf9Au\xc7\xcd#\xdb_\x05\xbe|-1|-1|1|0|2| (esc)
Multiple revisions of a file works
$ echo a >> foo
$ hg commit -m 'modify foo'
$ sqlite3 .hg/store/db.sqlite -init /dev/null << EOF
> SELECT * FROM filedata ORDER BY id ASC;
> EOF
1|1|foo|0|6/\xef(L\xe2\xca\x02\xae\xcc\x8d\xe6\xd5\xe8\xa1\xc3\xaf\x05V\xfe|-1|-1|0|0|1| (esc)
2|2|bar|0|\xb8\xe0/d3s\x80!\xa0e\xf9Au\xc7\xcd#\xdb_\x05\xbe|-1|-1|1|0|2| (esc)
3|1|foo|1|\xdd\xb3V\xcd\xde1p@\xf7\x8e\x90\xb8*\x8b,\xe9\x0e\xd6j+|0|-1|2|0|3|1 (esc)
$ cd ..