A new ancestor algorithm
The old ancestor algorithm could get fooled into returning ancestors
closer to root than it ought to. Hopefully this one, which strictly
orders its search by distance from room, will be foolproof.
# revlog.py - storage back-end for mercurial
#
# This provides efficient delta storage with O(1) retrieve and append
# and O(changes) merge between branches
#
# Copyright 2005 Matt Mackall <mpm@selenic.com>
#
# This software may be used and distributed according to the terms
# of the GNU General Public License, incorporated herein by reference.
import zlib, struct, sha, os, tempfile, binascii, heapq
from mercurial import mdiff
def hex(node): return binascii.hexlify(node)
def bin(node): return binascii.unhexlify(node)
def short(node): return hex(node[:4])
def compress(text):
if not text: return text
if len(text) < 44:
if text[0] == '\0': return text
return 'u' + text
bin = zlib.compress(text)
if len(bin) > len(text):
if text[0] == '\0': return text
return 'u' + text
return bin
def decompress(bin):
if not bin: return bin
t = bin[0]
if t == '\0': return bin
if t == 'x': return zlib.decompress(bin)
if t == 'u': return bin[1:]
raise "unknown compression type %s" % t
def hash(text, p1, p2):
l = [p1, p2]
l.sort()
return sha.sha(l[0] + l[1] + text).digest()
nullid = "\0" * 20
indexformat = ">4l20s20s20s"
class lazyparser:
def __init__(self, data):
self.data = data
self.s = struct.calcsize(indexformat)
self.l = len(data)/self.s
self.index = [None] * self.l
self.map = {nullid: -1}
def load(self, pos):
block = pos / 1000
i = block * 1000
end = min(self.l, i + 1000)
while i < end:
d = self.data[i * self.s: (i + 1) * self.s]
e = struct.unpack(indexformat, d)
self.index[i] = e
self.map[e[6]] = i
i += 1
class lazyindex:
def __init__(self, parser):
self.p = parser
def __len__(self):
return len(self.p.index)
def load(self, pos):
self.p.load(pos)
return self.p.index[pos]
def __getitem__(self, pos):
return self.p.index[pos] or self.load(pos)
def append(self, e):
self.p.index.append(e)
class lazymap:
def __init__(self, parser):
self.p = parser
def load(self, key):
n = self.p.data.find(key)
if n < 0: raise KeyError("node " + hex(key))
pos = n / self.p.s
self.p.load(pos)
def __contains__(self, key):
try:
self[key]
return True
except KeyError:
return False
def __iter__(self):
for i in xrange(self.p.l):
try:
yield self.p.index[i][6]
except:
self.p.load(i)
yield self.p.index[i][6]
def __getitem__(self, key):
try:
return self.p.map[key]
except KeyError:
try:
self.load(key)
return self.p.map[key]
except KeyError:
raise KeyError("node " + hex(key))
def __setitem__(self, key, val):
self.p.map[key] = val
class revlog:
def __init__(self, opener, indexfile, datafile):
self.indexfile = indexfile
self.datafile = datafile
self.opener = opener
self.cache = None
try:
i = self.opener(self.indexfile).read()
except IOError:
i = ""
if len(i) > 10000:
# big index, let's parse it on demand
parser = lazyparser(i)
self.index = lazyindex(parser)
self.nodemap = lazymap(parser)
else:
s = struct.calcsize(indexformat)
l = len(i) / s
self.index = [None] * l
m = [None] * l
n = 0
for f in xrange(0, len(i), s):
# offset, size, base, linkrev, p1, p2, nodeid
e = struct.unpack(indexformat, i[f:f + s])
m[n] = (e[6], n)
self.index[n] = e
n += 1
self.nodemap = dict(m)
self.nodemap[nullid] = -1
def tip(self): return self.node(len(self.index) - 1)
def count(self): return len(self.index)
def node(self, rev): return (rev < 0) and nullid or self.index[rev][6]
def rev(self, node): return self.nodemap[node]
def linkrev(self, node): return self.index[self.nodemap[node]][3]
def parents(self, node):
if node == nullid: return (nullid, nullid)
return self.index[self.nodemap[node]][4:6]
def start(self, rev): return self.index[rev][0]
def length(self, rev): return self.index[rev][1]
def end(self, rev): return self.start(rev) + self.length(rev)
def base(self, rev): return self.index[rev][2]
def lookup(self, id):
try:
rev = int(id)
return self.node(rev)
except ValueError:
c = []
for n in self.nodemap:
if id in hex(n):
c.append(n)
if len(c) > 1: raise KeyError("Ambiguous identifier")
if len(c) < 1: raise KeyError("No match found")
return c[0]
return None
def diff(self, a, b):
return mdiff.textdiff(a, b)
def patches(self, t, pl):
return mdiff.patches(t, pl)
def delta(self, node):
r = self.rev(node)
b = self.base(r)
if r == b:
return self.diff(self.revision(self.node(r - 1)),
self.revision(node))
else:
f = self.opener(self.datafile)
f.seek(self.start(r))
data = f.read(self.length(r))
return decompress(data)
def revision(self, node):
if node == nullid: return ""
if self.cache and self.cache[0] == node: return self.cache[2]
text = None
rev = self.rev(node)
start, length, base, link, p1, p2, node = self.index[rev]
end = start + length
if base != rev: start = self.start(base)
if self.cache and self.cache[1] >= base and self.cache[1] < rev:
base = self.cache[1]
start = self.start(base + 1)
text = self.cache[2]
last = 0
f = self.opener(self.datafile)
f.seek(start)
data = f.read(end - start)
if not text:
last = self.length(base)
text = decompress(data[:last])
bins = []
for r in xrange(base + 1, rev + 1):
s = self.length(r)
bins.append(decompress(data[last:last + s]))
last = last + s
text = mdiff.patches(text, bins)
if node != hash(text, p1, p2):
raise IOError("integrity check failed on %s:%d"
% (self.datafile, rev))
self.cache = (node, rev, text)
return text
def addrevision(self, text, transaction, link, p1=None, p2=None):
if text is None: text = ""
if p1 is None: p1 = self.tip()
if p2 is None: p2 = nullid
node = hash(text, p1, p2)
n = self.count()
t = n - 1
if n:
base = self.base(t)
start = self.start(base)
end = self.end(t)
prev = self.revision(self.tip())
d = self.diff(prev, text)
if self.patches(prev, [d]) != text:
raise AssertionError("diff failed")
data = compress(d)
dist = end - start + len(data)
# full versions are inserted when the needed deltas
# become comparable to the uncompressed text
if not n or dist > len(text) * 2:
data = compress(text)
base = n
else:
base = self.base(t)
offset = 0
if t >= 0:
offset = self.end(t)
e = (offset, len(data), base, link, p1, p2, node)
self.index.append(e)
self.nodemap[node] = n
entry = struct.pack(indexformat, *e)
transaction.add(self.datafile, e[0])
self.opener(self.datafile, "a").write(data)
transaction.add(self.indexfile, n * len(entry))
self.opener(self.indexfile, "a").write(entry)
self.cache = (node, n, text)
return node
def ancestor(self, a, b):
# calculate the distance of every node from root
dist = {nullid: 0}
for i in xrange(self.count()):
n = self.node(i)
p1, p2 = self.parents(n)
dist[n] = max(dist[p1], dist[p2]) + 1
# traverse ancestors in order of decreasing distance from root
def ancestors(node):
# we store negative distances because heap returns smallest member
h = [(-dist[node], node)]
seen = {}
earliest = self.count()
while h:
d, n = heapq.heappop(h)
r = self.rev(n)
if n not in seen:
seen[n] = 1
yield (-d, n)
for p in self.parents(n):
heapq.heappush(h, (-dist[p], p))
x = ancestors(a)
y = ancestors(b)
lx = x.next()
ly = y.next()
# increment each ancestor list until it is closer to root than
# the other, or they match
while 1:
if lx == ly:
return lx[1]
elif lx < ly:
ly = y.next()
elif lx > ly:
lx = x.next()
def group(self, linkmap):
# given a list of changeset revs, return a set of deltas and
# metadata corresponding to nodes. the first delta is
# parent(nodes[0]) -> nodes[0] the receiver is guaranteed to
# have this parent as it has all history before these
# changesets. parent is parent[0]
revs = []
needed = {}
# find file nodes/revs that match changeset revs
for i in xrange(0, self.count()):
if self.index[i][3] in linkmap:
revs.append(i)
needed[i] = 1
# if we don't have any revisions touched by these changesets, bail
if not revs: return struct.pack(">l", 0)
# add the parent of the first rev
p = self.parents(self.node(revs[0]))[0]
revs.insert(0, self.rev(p))
# for each delta that isn't contiguous in the log, we need to
# reconstruct the base, reconstruct the result, and then
# calculate the delta. We also need to do this where we've
# stored a full version and not a delta
for i in xrange(0, len(revs) - 1):
a, b = revs[i], revs[i + 1]
if a + 1 != b or self.base(b) == b:
for j in xrange(self.base(a), a + 1):
needed[j] = 1
for j in xrange(self.base(b), b + 1):
needed[j] = 1
# calculate spans to retrieve from datafile
needed = needed.keys()
needed.sort()
spans = []
for n in needed:
if n < 0: continue
o = self.start(n)
l = self.length(n)
spans.append((o, l, [(n, l)]))
# merge spans
merge = [spans.pop(0)]
while spans:
e = spans.pop(0)
f = merge[-1]
if e[0] == f[0] + f[1]:
merge[-1] = (f[0], f[1] + e[1], f[2] + e[2])
else:
merge.append(e)
# read spans in, divide up chunks
chunks = {}
for span in merge:
# we reopen the file for each span to make http happy for now
f = self.opener(self.datafile)
f.seek(span[0])
data = f.read(span[1])
# divide up the span
pos = 0
for r, l in span[2]:
chunks[r] = data[pos: pos + l]
pos += l
# helper to reconstruct intermediate versions
def construct(text, base, rev):
bins = [decompress(chunks[r]) for r in xrange(base + 1, rev + 1)]
return mdiff.patches(text, bins)
# build deltas
deltas = []
for d in xrange(0, len(revs) - 1):
a, b = revs[d], revs[d + 1]
n = self.node(b)
if a + 1 != b or self.base(b) == b:
if a >= 0:
base = self.base(a)
ta = decompress(chunks[self.base(a)])
ta = construct(ta, base, a)
else:
ta = ""
base = self.base(b)
if a > base:
base = a
tb = ta
else:
tb = decompress(chunks[self.base(b)])
tb = construct(tb, base, b)
d = self.diff(ta, tb)
else:
d = decompress(chunks[b])
p = self.parents(n)
meta = n + p[0] + p[1] + linkmap[self.linkrev(n)]
l = struct.pack(">l", len(meta) + len(d) + 4)
deltas.append(l + meta + d)
l = struct.pack(">l", sum(map(len, deltas)) + 4)
deltas.insert(0, l)
return "".join(deltas)
def addgroup(self, data, linkmapper, transaction):
# given a set of deltas, add them to the revision log. the
# first delta is against its parent, which should be in our
# log, the rest are against the previous delta.
if not data: return self.tip()
# retrieve the parent revision of the delta chain
chain = data[24:44]
if not chain in self.nodemap:
raise "unknown base %s" % short(chain[:4])
# track the base of the current delta log
r = self.count()
t = r - 1
base = prev = -1
start = end = 0
if r:
start = self.start(self.base(t))
end = self.end(t)
measure = self.length(self.base(t))
base = self.base(t)
prev = self.tip()
transaction.add(self.datafile, end)
transaction.add(self.indexfile, r * struct.calcsize(indexformat))
dfh = self.opener(self.datafile, "a")
ifh = self.opener(self.indexfile, "a")
# loop through our set of deltas
pos = 0
while pos < len(data):
l, node, p1, p2, cs = struct.unpack(">l20s20s20s20s",
data[pos:pos+84])
link = linkmapper(cs)
if node in self.nodemap:
raise "already have %s" % hex(node[:4])
delta = data[pos + 84:pos + l]
pos += l
# full versions are inserted when the needed deltas become
# comparable to the uncompressed text or when the previous
# version is not the one we have a delta against. We use
# the size of the previous full rev as a proxy for the
# current size.
if chain == prev:
cdelta = compress(delta)
if chain != prev or (end - start + len(cdelta)) > measure * 2:
# flush our writes here so we can read it in revision
dfh.flush()
ifh.flush()
text = self.revision(chain)
text = self.patches(text, [delta])
chk = self.addrevision(text, transaction, link, p1, p2)
if chk != node:
raise "consistency error adding group"
measure = len(text)
else:
e = (end, len(cdelta), self.base(t), link, p1, p2, node)
self.index.append(e)
self.nodemap[node] = r
dfh.write(cdelta)
ifh.write(struct.pack(indexformat, *e))
t, r, chain, prev = r, r + 1, node, node
start = self.start(self.base(t))
end = self.end(t)
dfh.close()
ifh.close()
return node