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fba9f14547
We were definitely being suboptimal here: we were constructing two full sets, one with the full set of common nodes (i.e. a graph traversal) and one with all nodes. Then we subtract one set from the other. This whole process is O(commits) and causes discovery to be significantly slower than it should be. Instead, keep track of common incrementally and keep undecided as small as possible. This makes discovery massively faster on large repos: on one such repo, 'hg debugdiscovery' over SSH with one commit missing on the client and five on the server went from 4.5 seconds to 1.5. (An 'hg debugdiscovery' with no commits missing on the client, i.e. connection startup time, was 1.2 seconds.)
250 lines
9.2 KiB
Python
250 lines
9.2 KiB
Python
# setdiscovery.py - improved discovery of common nodeset for mercurial
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#
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# Copyright 2010 Benoit Boissinot <bboissin@gmail.com>
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# and Peter Arrenbrecht <peter@arrenbrecht.ch>
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#
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# This software may be used and distributed according to the terms of the
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# GNU General Public License version 2 or any later version.
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"""
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Algorithm works in the following way. You have two repository: local and
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remote. They both contains a DAG of changelists.
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The goal of the discovery protocol is to find one set of node *common*,
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the set of nodes shared by local and remote.
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One of the issue with the original protocol was latency, it could
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potentially require lots of roundtrips to discover that the local repo was a
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subset of remote (which is a very common case, you usually have few changes
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compared to upstream, while upstream probably had lots of development).
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The new protocol only requires one interface for the remote repo: `known()`,
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which given a set of changelists tells you if they are present in the DAG.
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The algorithm then works as follow:
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- We will be using three sets, `common`, `missing`, `unknown`. Originally
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all nodes are in `unknown`.
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- Take a sample from `unknown`, call `remote.known(sample)`
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- For each node that remote knows, move it and all its ancestors to `common`
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- For each node that remote doesn't know, move it and all its descendants
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to `missing`
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- Iterate until `unknown` is empty
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There are a couple optimizations, first is instead of starting with a random
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sample of missing, start by sending all heads, in the case where the local
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repo is a subset, you computed the answer in one round trip.
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Then you can do something similar to the bisecting strategy used when
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finding faulty changesets. Instead of random samples, you can try picking
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nodes that will maximize the number of nodes that will be
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classified with it (since all ancestors or descendants will be marked as well).
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"""
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from node import nullid, nullrev
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from i18n import _
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import random
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import util, dagutil
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def _updatesample(dag, nodes, sample, always, quicksamplesize=0):
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# if nodes is empty we scan the entire graph
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if nodes:
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heads = dag.headsetofconnecteds(nodes)
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else:
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heads = dag.heads()
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dist = {}
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visit = util.deque(heads)
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seen = set()
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factor = 1
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while visit:
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curr = visit.popleft()
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if curr in seen:
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continue
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d = dist.setdefault(curr, 1)
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if d > factor:
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factor *= 2
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if d == factor:
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if curr not in always: # need this check for the early exit below
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sample.add(curr)
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if quicksamplesize and (len(sample) >= quicksamplesize):
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return
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seen.add(curr)
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for p in dag.parents(curr):
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if not nodes or p in nodes:
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dist.setdefault(p, d + 1)
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visit.append(p)
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def _setupsample(dag, nodes, size):
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if len(nodes) <= size:
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return set(nodes), None, 0
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always = dag.headsetofconnecteds(nodes)
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desiredlen = size - len(always)
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if desiredlen <= 0:
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# This could be bad if there are very many heads, all unknown to the
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# server. We're counting on long request support here.
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return always, None, desiredlen
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return always, set(), desiredlen
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def _takequicksample(dag, nodes, size, initial):
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always, sample, desiredlen = _setupsample(dag, nodes, size)
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if sample is None:
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return always
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if initial:
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fromset = None
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else:
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fromset = nodes
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_updatesample(dag, fromset, sample, always, quicksamplesize=desiredlen)
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sample.update(always)
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return sample
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def _takefullsample(dag, nodes, size):
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always, sample, desiredlen = _setupsample(dag, nodes, size)
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if sample is None:
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return always
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# update from heads
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_updatesample(dag, nodes, sample, always)
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# update from roots
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_updatesample(dag.inverse(), nodes, sample, always)
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assert sample
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sample = _limitsample(sample, desiredlen)
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if len(sample) < desiredlen:
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more = desiredlen - len(sample)
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sample.update(random.sample(list(nodes - sample - always), more))
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sample.update(always)
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return sample
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def _limitsample(sample, desiredlen):
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"""return a random subset of sample of at most desiredlen item"""
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if len(sample) > desiredlen:
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sample = set(random.sample(sample, desiredlen))
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return sample
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def findcommonheads(ui, local, remote,
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initialsamplesize=100,
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fullsamplesize=200,
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abortwhenunrelated=True):
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'''Return a tuple (common, anyincoming, remoteheads) used to identify
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missing nodes from or in remote.
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'''
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roundtrips = 0
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cl = local.changelog
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dag = dagutil.revlogdag(cl)
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# early exit if we know all the specified remote heads already
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ui.debug("query 1; heads\n")
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roundtrips += 1
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ownheads = dag.heads()
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sample = _limitsample(ownheads, initialsamplesize)
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# indices between sample and externalized version must match
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sample = list(sample)
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if remote.local():
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# stopgap until we have a proper localpeer that supports batch()
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srvheadhashes = remote.heads()
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yesno = remote.known(dag.externalizeall(sample))
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elif remote.capable('batch'):
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batch = remote.batch()
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srvheadhashesref = batch.heads()
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yesnoref = batch.known(dag.externalizeall(sample))
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batch.submit()
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srvheadhashes = srvheadhashesref.value
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yesno = yesnoref.value
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else:
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# compatibility with pre-batch, but post-known remotes during 1.9
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# development
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srvheadhashes = remote.heads()
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sample = []
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if cl.tip() == nullid:
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if srvheadhashes != [nullid]:
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return [nullid], True, srvheadhashes
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return [nullid], False, []
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# start actual discovery (we note this before the next "if" for
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# compatibility reasons)
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ui.status(_("searching for changes\n"))
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srvheads = dag.internalizeall(srvheadhashes, filterunknown=True)
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if len(srvheads) == len(srvheadhashes):
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ui.debug("all remote heads known locally\n")
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return (srvheadhashes, False, srvheadhashes,)
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if sample and len(ownheads) <= initialsamplesize and util.all(yesno):
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ui.note(_("all local heads known remotely\n"))
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ownheadhashes = dag.externalizeall(ownheads)
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return (ownheadhashes, True, srvheadhashes,)
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# full blown discovery
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# own nodes where I don't know if remote knows them
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undecided = dag.nodeset()
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# own nodes I know we both know
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# treat remote heads (and maybe own heads) as a first implicit sample
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# response
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common = cl.incrementalmissingrevs(srvheads)
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commoninsample = set(n for i, n in enumerate(sample) if yesno[i])
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common.addbases(commoninsample)
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undecided = set(common.missingancestors(ownheads))
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# own nodes I know remote lacks
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missing = set()
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full = False
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while undecided:
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if sample:
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missinginsample = [n for i, n in enumerate(sample) if not yesno[i]]
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missing.update(dag.descendantset(missinginsample, missing))
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undecided.difference_update(missing)
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if not undecided:
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break
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if full:
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ui.note(_("sampling from both directions\n"))
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sample = _takefullsample(dag, undecided, size=fullsamplesize)
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targetsize = fullsamplesize
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elif common.hasbases():
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# use cheapish initial sample
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ui.debug("taking initial sample\n")
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sample = _takefullsample(dag, undecided, size=fullsamplesize)
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targetsize = fullsamplesize
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else:
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# use even cheaper initial sample
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ui.debug("taking quick initial sample\n")
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sample = _takequicksample(dag, undecided, size=initialsamplesize,
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initial=True)
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targetsize = initialsamplesize
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sample = _limitsample(sample, targetsize)
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roundtrips += 1
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ui.progress(_('searching'), roundtrips, unit=_('queries'))
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ui.debug("query %i; still undecided: %i, sample size is: %i\n"
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% (roundtrips, len(undecided), len(sample)))
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# indices between sample and externalized version must match
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sample = list(sample)
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yesno = remote.known(dag.externalizeall(sample))
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full = True
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if sample:
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commoninsample = set(n for i, n in enumerate(sample) if yesno[i])
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common.addbases(commoninsample)
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common.removeancestorsfrom(undecided)
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# heads(common) == heads(common.bases) since common represents common.bases
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# and all its ancestors
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result = dag.headsetofconnecteds(common.bases)
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# common.bases can include nullrev, but our contract requires us to not
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# return any heads in that case, so discard that
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result.discard(nullrev)
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ui.progress(_('searching'), None)
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ui.debug("%d total queries\n" % roundtrips)
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if not result and srvheadhashes != [nullid]:
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if abortwhenunrelated:
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raise util.Abort(_("repository is unrelated"))
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else:
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ui.warn(_("warning: repository is unrelated\n"))
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return (set([nullid]), True, srvheadhashes,)
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anyincoming = (srvheadhashes != [nullid])
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return dag.externalizeall(result), anyincoming, srvheadhashes
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