Mercurial > hg
view mercurial/treediscovery.py @ 29322:66dbdd3cc2b9 stable
bdiff: extend matches across popular lines
For very large diffs that have large numbers of identical lines (JSON
dumps) that also have large blocks of identical text, bdiff could become
confused about which block matches which because it can only match
very limited regions. The result is very large diffs for small sets of edits.
The earlier recursion rebalancing fix made this behavior more frequent because
it's now more prone to match block 1 to block 2. One frequent user of
large JSON files reported being unable to pass the resulting diffs
through their code review system.
Prior to this change, bdiff would calculate the length of a match at
(i, j) as 1 + length found at (i-1, j-1). With large number of popular
(ignored) lines, this often meant matches couldn't be extended
backwards at all and thus all matching regions were very small.
Disabling the popularity threshold is not an option because it brings
back quadratic behavior.
Instead, we extend a match backwards until we either found a previously
discovered match or we find a mismatching line. This thus successfully
bridges over any popular lines inside and before a matching region.
The larger regions then significant reduce the probability of confusion.
author | Matt Mackall <mpm@selenic.com> |
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date | Thu, 02 Jun 2016 17:09:06 -0500 |
parents | 56b2bcea2529 |
children | 0ed11f9368fd |
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# discovery.py - protocol changeset discovery functions # # Copyright 2010 Matt Mackall <mpm@selenic.com> # # This software may be used and distributed according to the terms of the # GNU General Public License version 2 or any later version. from __future__ import absolute_import import collections from .i18n import _ from .node import ( nullid, short, ) from . import ( error, ) def findcommonincoming(repo, remote, heads=None, force=False): """Return a tuple (common, fetch, heads) used to identify the common subset of nodes between repo and remote. "common" is a list of (at least) the heads of the common subset. "fetch" is a list of roots of the nodes that would be incoming, to be supplied to changegroupsubset. "heads" is either the supplied heads, or else the remote's heads. """ knownnode = repo.changelog.hasnode search = [] fetch = set() seen = set() seenbranch = set() base = set() if not heads: heads = remote.heads() if repo.changelog.tip() == nullid: base.add(nullid) if heads != [nullid]: return [nullid], [nullid], list(heads) return [nullid], [], heads # assume we're closer to the tip than the root # and start by examining the heads repo.ui.status(_("searching for changes\n")) unknown = [] for h in heads: if not knownnode(h): unknown.append(h) else: base.add(h) if not unknown: return list(base), [], list(heads) req = set(unknown) reqcnt = 0 # search through remote branches # a 'branch' here is a linear segment of history, with four parts: # head, root, first parent, second parent # (a branch always has two parents (or none) by definition) unknown = collections.deque(remote.branches(unknown)) while unknown: r = [] while unknown: n = unknown.popleft() if n[0] in seen: continue repo.ui.debug("examining %s:%s\n" % (short(n[0]), short(n[1]))) if n[0] == nullid: # found the end of the branch pass elif n in seenbranch: repo.ui.debug("branch already found\n") continue elif n[1] and knownnode(n[1]): # do we know the base? repo.ui.debug("found incomplete branch %s:%s\n" % (short(n[0]), short(n[1]))) search.append(n[0:2]) # schedule branch range for scanning seenbranch.add(n) else: if n[1] not in seen and n[1] not in fetch: if knownnode(n[2]) and knownnode(n[3]): repo.ui.debug("found new changeset %s\n" % short(n[1])) fetch.add(n[1]) # earliest unknown for p in n[2:4]: if knownnode(p): base.add(p) # latest known for p in n[2:4]: if p not in req and not knownnode(p): r.append(p) req.add(p) seen.add(n[0]) if r: reqcnt += 1 repo.ui.progress(_('searching'), reqcnt, unit=_('queries')) repo.ui.debug("request %d: %s\n" % (reqcnt, " ".join(map(short, r)))) for p in xrange(0, len(r), 10): for b in remote.branches(r[p:p + 10]): repo.ui.debug("received %s:%s\n" % (short(b[0]), short(b[1]))) unknown.append(b) # do binary search on the branches we found while search: newsearch = [] reqcnt += 1 repo.ui.progress(_('searching'), reqcnt, unit=_('queries')) for n, l in zip(search, remote.between(search)): l.append(n[1]) p = n[0] f = 1 for i in l: repo.ui.debug("narrowing %d:%d %s\n" % (f, len(l), short(i))) if knownnode(i): if f <= 2: repo.ui.debug("found new branch changeset %s\n" % short(p)) fetch.add(p) base.add(i) else: repo.ui.debug("narrowed branch search to %s:%s\n" % (short(p), short(i))) newsearch.append((p, i)) break p, f = i, f * 2 search = newsearch # sanity check our fetch list for f in fetch: if knownnode(f): raise error.RepoError(_("already have changeset ") + short(f[:4])) base = list(base) if base == [nullid]: if force: repo.ui.warn(_("warning: repository is unrelated\n")) else: raise error.Abort(_("repository is unrelated")) repo.ui.debug("found new changesets starting at " + " ".join([short(f) for f in fetch]) + "\n") repo.ui.progress(_('searching'), None) repo.ui.debug("%d total queries\n" % reqcnt) return base, list(fetch), heads