nodemap: introduce append-only incremental update of the persistent data
Rewriting the full nodemap for each transaction has a cost we would like to
avoid. We introduce a new way to write persistent nodemap data by adding new
information at the end for file. Any new and updated block as added at the end
of the file. The last block is the new root node.
With this method, some of the block already on disk get "dereferenced" and
become dead data. In later changesets, We'll start tracking the amount of dead
data to eventually re-generate a full nodemap.
Differential Revision: https://phab.mercurial-scm.org/D7886
from __future__ import absolute_import, print_function
import collections
import struct
import unittest
from mercurial import mdiff
class diffreplace(collections.namedtuple('diffreplace', 'start end from_ to')):
def __repr__(self):
return 'diffreplace(%r, %r, %r, %r)' % self
class BdiffTests(unittest.TestCase):
def assert_bdiff_applies(self, a, b):
d = mdiff.textdiff(a, b)
c = a
if d:
c = mdiff.patches(a, [d])
self.assertEqual(
c,
b,
(
"bad diff+patch result from\n %r to\n "
"%r: \nbdiff: %r\npatched: %r" % (a, b, d, c[:200])
),
)
def assert_bdiff(self, a, b):
self.assert_bdiff_applies(a, b)
self.assert_bdiff_applies(b, a)
def test_bdiff_basic(self):
cases = [
(b"a\nc\n\n\n\n", b"a\nb\n\n\n"),
(b"a\nb\nc\n", b"a\nc\n"),
(b"", b""),
(b"a\nb\nc", b"a\nb\nc"),
(b"a\nb\nc\nd\n", b"a\nd\n"),
(b"a\nb\nc\nd\n", b"a\nc\ne\n"),
(b"a\nb\nc\n", b"a\nc\n"),
(b"a\n", b"c\na\nb\n"),
(b"a\n", b""),
(b"a\n", b"b\nc\n"),
(b"a\n", b"c\na\n"),
(b"", b"adjfkjdjksdhfksj"),
(b"", b"ab"),
(b"", b"abc"),
(b"a", b"a"),
(b"ab", b"ab"),
(b"abc", b"abc"),
(b"a\n", b"a\n"),
(b"a\nb", b"a\nb"),
]
for a, b in cases:
self.assert_bdiff(a, b)
def showdiff(self, a, b):
bin = mdiff.textdiff(a, b)
pos = 0
q = 0
actions = []
while pos < len(bin):
p1, p2, l = struct.unpack(">lll", bin[pos : pos + 12])
pos += 12
if p1:
actions.append(a[q:p1])
actions.append(diffreplace(p1, p2, a[p1:p2], bin[pos : pos + l]))
pos += l
q = p2
if q < len(a):
actions.append(a[q:])
return actions
def test_issue1295(self):
cases = [
(
b"x\n\nx\n\nx\n\nx\n\nz\n",
b"x\n\nx\n\ny\n\nx\n\nx\n\nz\n",
[
b'x\n\nx\n\n',
diffreplace(6, 6, b'', b'y\n\n'),
b'x\n\nx\n\nz\n',
],
),
(
b"x\n\nx\n\nx\n\nx\n\nz\n",
b"x\n\nx\n\ny\n\nx\n\ny\n\nx\n\nz\n",
[
b'x\n\nx\n\n',
diffreplace(6, 6, b'', b'y\n\n'),
b'x\n\n',
diffreplace(9, 9, b'', b'y\n\n'),
b'x\n\nz\n',
],
),
]
for old, new, want in cases:
self.assertEqual(self.showdiff(old, new), want)
def test_issue1295_varies_on_pure(self):
# we should pick up abbbc. rather than bc.de as the longest match
got = self.showdiff(
b"a\nb\nb\nb\nc\n.\nd\ne\n.\nf\n",
b"a\nb\nb\na\nb\nb\nb\nc\n.\nb\nc\n.\nd\ne\nf\n",
)
want_c = [
b'a\nb\nb\n',
diffreplace(6, 6, b'', b'a\nb\nb\nb\nc\n.\n'),
b'b\nc\n.\nd\ne\n',
diffreplace(16, 18, b'.\n', b''),
b'f\n',
]
want_pure = [
diffreplace(0, 0, b'', b'a\nb\nb\n'),
b'a\nb\nb\nb\nc\n.\n',
diffreplace(12, 12, b'', b'b\nc\n.\n'),
b'd\ne\n',
diffreplace(16, 18, b'.\n', b''),
b'f\n',
]
self.assertTrue(
got in (want_c, want_pure),
'got: %r, wanted either %r or %r' % (got, want_c, want_pure),
)
def test_fixws(self):
cases = [
(b" \ta\r b\t\n", b"ab\n", 1),
(b" \ta\r b\t\n", b" a b\n", 0),
(b"", b"", 1),
(b"", b"", 0),
]
for a, b, allws in cases:
c = mdiff.fixws(a, allws)
self.assertEqual(
c, b, 'fixws(%r) want %r got %r (allws=%r)' % (a, b, c, allws)
)
def test_nice_diff_for_trivial_change(self):
self.assertEqual(
self.showdiff(
b''.join(b'<%d\n-\n' % i for i in range(5)),
b''.join(b'>%d\n-\n' % i for i in range(5)),
),
[
diffreplace(0, 3, b'<0\n', b'>0\n'),
b'-\n',
diffreplace(5, 8, b'<1\n', b'>1\n'),
b'-\n',
diffreplace(10, 13, b'<2\n', b'>2\n'),
b'-\n',
diffreplace(15, 18, b'<3\n', b'>3\n'),
b'-\n',
diffreplace(20, 23, b'<4\n', b'>4\n'),
b'-\n',
],
)
def test_prefer_appending(self):
# 1 line to 3 lines
self.assertEqual(
self.showdiff(b'a\n', b'a\n' * 3),
[b'a\n', diffreplace(2, 2, b'', b'a\na\n')],
)
# 1 line to 5 lines
self.assertEqual(
self.showdiff(b'a\n', b'a\n' * 5),
[b'a\n', diffreplace(2, 2, b'', b'a\na\na\na\n')],
)
def test_prefer_removing_trailing(self):
# 3 lines to 1 line
self.assertEqual(
self.showdiff(b'a\n' * 3, b'a\n'),
[b'a\n', diffreplace(2, 6, b'a\na\n', b'')],
)
# 5 lines to 1 line
self.assertEqual(
self.showdiff(b'a\n' * 5, b'a\n'),
[b'a\n', diffreplace(2, 10, b'a\na\na\na\n', b'')],
)
if __name__ == '__main__':
import silenttestrunner
silenttestrunner.main(__name__)