Mercurial > hg
view mercurial/revlog.py @ 373:67081329d49a
Change the size of the short hash representation
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Change the size of the short hash representation
First note that this number doesn't really matter, as we always check
for ambiguous short hash ids.
Here's the math on collision probability:
>>> import math
>>> def p(f, n): return 1 - (1 / math.exp(n**2/(2*f)))
...
>>> p(2**32, 30000.0)
0.09947179164613551 # with 30000 changesets (BKCVS), we have a 9% chance
>>> p(2**32, 65000.0)
0.38850881217977273 # and with a full import from BK, we'd have a 39% chance
>>> p(2**40, 1e6)
0.36539171908447321 # we'd like to be "safe" for 1M csets, so 40 isn't enough
>>> p(2**48, 1e6)
0.001774780051374103 # But 48 looks good
>>> p(2**48, 1e7)
0.16275260939624481
>>> p(2**48, 5e6)
0.043437281083569146
>>> p(2**48, 2e6)
0.0070802434913129764
>>> p(2**48, 3e6)
0.01586009440574343
manifest hash: 24d9f928a463f46708b0e11fb781d5a241851424
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author | mpm@selenic.com |
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date | Wed, 15 Jun 2005 21:11:40 -0800 |
parents | c90385d82aec |
children | e5d769afd3ef |
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# 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, 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[:6]) 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, revlog): self.data = data self.s = struct.calcsize(indexformat) self.l = len(data)/self.s self.index = [None] * self.l self.map = {nullid: -1} self.all = 0 self.revlog = revlog def load(self, pos=None): if self.all: return if pos is not None: block = pos / 1000 i = block * 1000 end = min(self.l, i + 1000) else: self.all = 1 i = 0 end = self.l self.revlog.index = self.index self.revlog.nodemap = self.map 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): if self.p.all: return 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): self.p.load() return key in self.p.map 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) 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 heads(self): p = {} h = [] for r in range(self.count() - 1, -1, -1): n = self.node(r) if n not in p: h.append(n) for pn in self.parents(n): p[pn] = 1 return h def children(self, node): c = [] p = self.rev(node) for r in range(p + 1, self.count()): n = self.node(r) for pn in self.parents(n): if pn == p: c.append(p) continue elif pn == nullid: continue return c 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) if node in self.nodemap: return node 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) 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: yield struct.pack(">l", 0) return # 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 = [] oo = -1 ol = 0 for n in needed: if n < 0: continue o = self.start(n) l = self.length(n) if oo + ol == o: # can we merge with the previous? nl = spans[-1][2] nl.append((n, l)) ol += l spans[-1] = (oo, ol, nl) else: oo = o ol = l spans.append((oo, ol, [(n, l)])) # read spans in, divide up chunks chunks = {} for span in spans: # 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] = decompress(data[pos: pos + l]) pos += l # helper to reconstruct intermediate versions def construct(text, base, rev): bins = [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) # do we need to construct a new delta? if a + 1 != b or self.base(b) == b: if a >= 0: base = self.base(a) ta = chunks[self.base(a)] ta = construct(ta, base, a) else: ta = "" base = self.base(b) if a > base: base = a tb = ta else: tb = chunks[self.base(b)] tb = construct(tb, base, b) d = self.diff(ta, tb) else: d = 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) yield l yield meta yield d yield struct.pack(">l", 0) def addgroup(self, revs, linkmapper, transaction, unique = 0): # 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. # track the base of the current delta log r = self.count() t = r - 1 node = nullid 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 chain = None for chunk in revs: node, p1, p2, cs = struct.unpack("20s20s20s20s", chunk[:80]) link = linkmapper(cs) if node in self.nodemap: # this can happen if two branches make the same change if unique: raise "already have %s" % hex(node[:4]) continue delta = chunk[80:] if not chain: # retrieve the parent revision of the delta chain chain = p1 if not chain in self.nodemap: raise "unknown base %s" % short(chain[:4]) # 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