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
import unittest
from mercurial import policy
PartialDiscovery = policy.importrust('discovery', member='PartialDiscovery')
try:
from mercurial.cext import parsers as cparsers
except ImportError:
cparsers = None
# picked from test-parse-index2, copied rather than imported
# so that it stays stable even if test-parse-index2 changes or disappears.
data_non_inlined = (
b'\x00\x00\x00\x01\x00\x00\x00\x00\x00\x01D\x19'
b'\x00\x07e\x12\x00\x00\x00\x00\x00\x00\x00\x00\xff\xff\xff\xff'
b'\xff\xff\xff\xff\xd1\xf4\xbb\xb0\xbe\xfc\x13\xbd\x8c\xd3\x9d'
b'\x0f\xcd\xd9;\x8c\x07\x8cJ/\x00\x00\x00\x00\x00\x00\x00\x00\x00'
b'\x00\x00\x00\x00\x00\x00\x01D\x19\x00\x00\x00\x00\x00\xdf\x00'
b'\x00\x01q\x00\x00\x00\x01\x00\x00\x00\x01\x00\x00\x00\x00\xff'
b'\xff\xff\xff\xc1\x12\xb9\x04\x96\xa4Z1t\x91\xdfsJ\x90\xf0\x9bh'
b'\x07l&\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00'
b'\x00\x01D\xf8\x00\x00\x00\x00\x01\x1b\x00\x00\x01\xb8\x00\x00'
b'\x00\x01\x00\x00\x00\x02\x00\x00\x00\x01\xff\xff\xff\xff\x02\n'
b'\x0e\xc6&\xa1\x92\xae6\x0b\x02i\xfe-\xe5\xbao\x05\xd1\xe7\x00'
b'\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x01F'
b'\x13\x00\x00\x00\x00\x01\xec\x00\x00\x03\x06\x00\x00\x00\x01'
b'\x00\x00\x00\x03\x00\x00\x00\x02\xff\xff\xff\xff\x12\xcb\xeby1'
b'\xb6\r\x98B\xcb\x07\xbd`\x8f\x92\xd9\xc4\x84\xbdK\x00\x00\x00'
b'\x00\x00\x00\x00\x00\x00\x00\x00\x00'
)
class fakechangelog:
def __init__(self, idx):
self.index = idx
class fakerepo:
def __init__(self, idx):
"""Just make so that self.changelog.index is the given idx."""
self.changelog = fakechangelog(idx)
@unittest.skipIf(
PartialDiscovery is None or cparsers is None,
"rustext or the C Extension parsers module "
"discovery relies on is not available",
)
class rustdiscoverytest(unittest.TestCase):
"""Test the correctness of binding to Rust code.
This test is merely for the binding to Rust itself: extraction of
Python variable, giving back the results etc.
It is not meant to test the algorithmic correctness of the provided
methods. Hence the very simple embedded index data is good enough.
Algorithmic correctness is asserted by the Rust unit tests.
"""
def parseindex(self):
return cparsers.parse_index2(data_non_inlined, False)[0]
def repo(self):
return fakerepo(self.parseindex())
def testindex(self):
idx = self.parseindex()
# checking our assumptions about the index binary data:
self.assertEqual(
{i: (r[5], r[6]) for i, r in enumerate(idx)},
{0: (-1, -1), 1: (0, -1), 2: (1, -1), 3: (2, -1)},
)
def testaddcommonsmissings(self):
disco = PartialDiscovery(self.repo(), [3], True)
self.assertFalse(disco.hasinfo())
self.assertFalse(disco.iscomplete())
disco.addcommons([1])
self.assertTrue(disco.hasinfo())
self.assertFalse(disco.iscomplete())
disco.addmissings([2])
self.assertTrue(disco.hasinfo())
self.assertTrue(disco.iscomplete())
self.assertEqual(disco.commonheads(), {1})
def testaddmissingsstats(self):
disco = PartialDiscovery(self.repo(), [3], True)
self.assertIsNone(disco.stats()['undecided'], None)
disco.addmissings([2])
self.assertEqual(disco.stats()['undecided'], 2)
def testaddinfocommonfirst(self):
disco = PartialDiscovery(self.repo(), [3], True)
disco.addinfo([(1, True), (2, False)])
self.assertTrue(disco.hasinfo())
self.assertTrue(disco.iscomplete())
self.assertEqual(disco.commonheads(), {1})
def testaddinfomissingfirst(self):
disco = PartialDiscovery(self.repo(), [3], True)
disco.addinfo([(2, False), (1, True)])
self.assertTrue(disco.hasinfo())
self.assertTrue(disco.iscomplete())
self.assertEqual(disco.commonheads(), {1})
def testinitnorandom(self):
PartialDiscovery(self.repo(), [3], True, randomize=False)
if __name__ == '__main__':
import silenttestrunner
silenttestrunner.main(__name__)