Mercurial > hg > mercurial-crew-with-dirclash
view mercurial/revlog.py @ 1264:be4a14bfaa9c
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author | Thomas Arendsen Hein <thomas@intevation.de> |
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date | Fri, 16 Sep 2005 21:34:18 +0200 |
parents | eb3cc5e2eb89 |
children | b3d44e9b3092 |
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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 import mdiff from node import * def hash(text, p1, p2): """generate a hash from the given text and its parent hashes This hash combines both the current file contents and its history in a manner that makes it easy to distinguish nodes with the same content in the revision graph. """ l = [p1, p2] l.sort() s = sha.new(l[0]) s.update(l[1]) s.update(text) return s.digest() def compress(text): """ generate a possibly-compressed representation of 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): """ decompress the given input """ 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 RevlogError("unknown compression type %s" % t) indexformat = ">4l20s20s20s" class lazyparser: """ this class avoids the need to parse the entirety of large indices By default we parse and load 1000 entries at a time. If no position is specified, we load the whole index, and replace the lazy objects in revlog with the underlying objects for efficiency in cases where we look at most of the nodes. """ 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: """a lazy version of the index array""" 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: """a lazy version of the node map""" 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(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): yield nullid 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 RevlogError(Exception): pass class revlog: """ the underlying revision storage object A revlog consists of two parts, an index and the revision data. The index is a file with a fixed record size containing information on each revision, includings its nodeid (hash), the nodeids of its parents, the position and offset of its data within the data file, and the revision it's based on. Finally, each entry contains a linkrev entry that can serve as a pointer to external data. The revision data itself is a linear collection of data chunks. Each chunk represents a revision and is usually represented as a delta against the previous chunk. To bound lookup time, runs of deltas are limited to about 2 times the length of the original version data. This makes retrieval of a version proportional to its size, or O(1) relative to the number of revisions. Both pieces of the revlog are written to in an append-only fashion, which means we never need to rewrite a file to insert or remove data, and can use some simple techniques to avoid the need for locking while reading. """ def __init__(self, opener, indexfile, datafile): """ create a revlog object opener is a function that abstracts the file opening operation and can be used to implement COW semantics or the like. """ 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): try: return self.nodemap[node] except KeyError: raise RevlogError('%s: no node %s' % (self.indexfile, hex(node))) def linkrev(self, node): return self.index[self.rev(node)][3] def parents(self, node): if node == nullid: return (nullid, nullid) return self.index[self.rev(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 reachable(self, rev, stop=None): reachable = {} visit = [rev] reachable[rev] = 1 if stop: stopn = self.rev(stop) else: stopn = 0 while visit: n = visit.pop(0) if n == stop: continue if n == nullid: continue for p in self.parents(n): if self.rev(p) < stopn: continue if p not in reachable: reachable[p] = 1 visit.append(p) return reachable def heads(self, stop=None): """return the list of all nodes that have no children""" p = {} h = [] stoprev = 0 if stop and stop in self.nodemap: stoprev = self.rev(stop) for r in range(self.count() - 1, -1, -1): n = self.node(r) if n not in p: h.append(n) if n == stop: break if r < stoprev: break for pn in self.parents(n): p[pn] = 1 return h def children(self, node): """find the children of a given 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 == node: c.append(n) continue elif pn == nullid: continue return c def lookup(self, id): """locate a node based on revision number or subset of hex nodeid""" try: rev = int(id) if str(rev) != id: raise ValueError if rev < 0: rev = self.count() + rev if rev < 0 or rev >= self.count(): raise ValueError return self.node(rev) except (ValueError, OverflowError): c = [] for n in self.nodemap: if hex(n).startswith(id): 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 a delta between two revisions""" return mdiff.textdiff(a, b) def patches(self, t, pl): """apply a list of patches to a string""" return mdiff.patches(t, pl) def delta(self, node): """return or calculate a delta between a node and its predecessor""" 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): """return an uncompressed revision of a given""" if node == nullid: return "" if self.cache and self.cache[0] == node: return self.cache[2] # look up what we need to read 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) # do we have useful data cached? 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 text is None: 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 RevlogError("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, d=None): """add a revision to the log text - the revision data to add transaction - the transaction object used for rollback link - the linkrev data to add p1, p2 - the parent nodeids of the revision d - an optional precomputed delta """ 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) if not d: 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 least common ancestor of nodes a and 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) if n not in seen: seen[n] = 1 r = self.rev(n) yield (-d, r, 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[2] elif lx < ly: ly = y.next() elif lx > ly: lx = x.next() def group(self, linkmap): """calculate a delta group 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): """ add a delta group 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 = measure = 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 RevlogError("already have %s" % hex(node[:4])) chain = node continue delta = chunk[80:] if not chain: # retrieve the parent revision of the delta chain chain = p1 if not chain in self.nodemap: raise RevlogError("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 RevlogError("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