Mercurial > hg
view mercurial/setdiscovery.py @ 42043:1fac9b931d46
compression: introduce a `storage.revlog.zlib.level` configuration
This option control the zlib compression level used when compression revlog
chunk.
This is also a good excuse to pave the way for a similar configuration option
for the zstd compression engine. Having a dedicated option for each compression
algorithm is useful because they don't support the same range of values.
Using a higher zlib compression impact CPU consumption at compression time, but
does not directly affected decompression time. However dealing with small
compressed chunk can directly help decompression and indirectly help other
revlog logic.
I ran some basic test on repositories using different level. I am using the
mercurial, pypy, netbeans and mozilla-central clone from our benchmark suite.
All tested repository use sparse-revlog and got all their delta recomputed.
The different compression level has a small effect on the repository size
(about 10% variation in the total range). My quick analysis is that revlog
mostly store small delta, that are not affected by the compression level much.
So the variation probably mostly comes from better compression of the snapshots
revisions, and snapshot revision only represent a small portion of the
repository content.
I also made some basic timings measurements. The "read" timings are gathered using
simple run of `hg perfrevlogrevisions`, the "write" timings using `hg
perfrevlogwrite` (restricted to the last 5000 revisions for netbeans and
mozilla central). The timings are gathered on a generic machine, (not one of
our performance locked machine), so small variation might not be meaningful.
However large trend remains relevant.
Keep in mind that these numbers are not pure compression/decompression time.
They also involve the full revlog logic. In particular the difference in chunk
size has an impact on the delta chain structure, affecting performance when
writing or reading them.
On read/write performance, the compression level has a bigger impact.
Counter-intuitively, the higher compression levels improve "write" performance
for the large repositories in our tested setting. Maybe because the last 5000
delta chain end up having a very different shape in this specific spot? Or maybe
because of a more general trend of better delta chains thanks to the smaller
chunk and snapshot.
This series does not intend to change the default compression level. However,
these result call for a deeper analysis of this performance difference in the
future.
Full data
=========
repo level .hg/store size 00manifest.d read write
----------------------------------------------------------------
mercurial 1 49,402,813 5,963,475 0.170159 53.250304
mercurial 6 47,197,397 5,875,730 0.182820 56.264320
mercurial 9 47,121,596 5,849,781 0.189219 56.293612
pypy 1 370,830,572 28,462,425 2.679217 460.721984
pypy 6 340,112,317 27,648,747 2.768691 467.537158
pypy 9 338,360,736 27,639,003 2.763495 476.589918
netbeans 1 1,281,847,810 165,495,457 122.477027 520.560316
netbeans 6 1,205,284,353 159,161,207 139.876147 715.930400
netbeans 9 1,197,135,671 155,034,586 141.620281 678.297064
mozilla 1 2,775,497,186 298,527,987 147.867662 751.263721
mozilla 6 2,596,856,420 286,597,671 170.572118 987.056093
mozilla 9 2,587,542,494 287,018,264 163.622338 739.803002
author | Pierre-Yves David <pierre-yves.david@octobus.net> |
---|---|
date | Wed, 27 Mar 2019 18:35:27 +0100 |
parents | 0d467e4de4ae |
children | 362726923ba3 |
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# setdiscovery.py - improved discovery of common nodeset for mercurial # # Copyright 2010 Benoit Boissinot <bboissin@gmail.com> # and Peter Arrenbrecht <peter@arrenbrecht.ch> # # This software may be used and distributed according to the terms of the # GNU General Public License version 2 or any later version. """ Algorithm works in the following way. You have two repository: local and remote. They both contains a DAG of changelists. The goal of the discovery protocol is to find one set of node *common*, the set of nodes shared by local and remote. One of the issue with the original protocol was latency, it could potentially require lots of roundtrips to discover that the local repo was a subset of remote (which is a very common case, you usually have few changes compared to upstream, while upstream probably had lots of development). The new protocol only requires one interface for the remote repo: `known()`, which given a set of changelists tells you if they are present in the DAG. The algorithm then works as follow: - We will be using three sets, `common`, `missing`, `unknown`. Originally all nodes are in `unknown`. - Take a sample from `unknown`, call `remote.known(sample)` - For each node that remote knows, move it and all its ancestors to `common` - For each node that remote doesn't know, move it and all its descendants to `missing` - Iterate until `unknown` is empty There are a couple optimizations, first is instead of starting with a random sample of missing, start by sending all heads, in the case where the local repo is a subset, you computed the answer in one round trip. Then you can do something similar to the bisecting strategy used when finding faulty changesets. Instead of random samples, you can try picking nodes that will maximize the number of nodes that will be classified with it (since all ancestors or descendants will be marked as well). """ from __future__ import absolute_import import collections import random from .i18n import _ from .node import ( nullid, nullrev, ) from . import ( error, util, ) def _updatesample(revs, heads, sample, parentfn, quicksamplesize=0): """update an existing sample to match the expected size The sample is updated with revs exponentially distant from each head of the <revs> set. (H~1, H~2, H~4, H~8, etc). If a target size is specified, the sampling will stop once this size is reached. Otherwise sampling will happen until roots of the <revs> set are reached. :revs: set of revs we want to discover (if None, assume the whole dag) :heads: set of DAG head revs :sample: a sample to update :parentfn: a callable to resolve parents for a revision :quicksamplesize: optional target size of the sample""" dist = {} visit = collections.deque(heads) seen = set() factor = 1 while visit: curr = visit.popleft() if curr in seen: continue d = dist.setdefault(curr, 1) if d > factor: factor *= 2 if d == factor: sample.add(curr) if quicksamplesize and (len(sample) >= quicksamplesize): return seen.add(curr) for p in parentfn(curr): if p != nullrev and (not revs or p in revs): dist.setdefault(p, d + 1) visit.append(p) def _limitsample(sample, desiredlen): """return a random subset of sample of at most desiredlen item""" if len(sample) > desiredlen: sample = set(random.sample(sample, desiredlen)) return sample class partialdiscovery(object): """an object representing ongoing discovery Feed with data from the remote repository, this object keep track of the current set of changeset in various states: - common: revs also known remotely - undecided: revs we don't have information on yet - missing: revs missing remotely (all tracked revisions are known locally) """ def __init__(self, repo, targetheads): self._repo = repo self._targetheads = targetheads self._common = repo.changelog.incrementalmissingrevs() self._undecided = None self.missing = set() self._childrenmap = None def addcommons(self, commons): """registrer nodes known as common""" self._common.addbases(commons) if self._undecided is not None: self._common.removeancestorsfrom(self._undecided) def addmissings(self, missings): """registrer some nodes as missing""" newmissing = self._repo.revs('%ld::%ld', missings, self.undecided) if newmissing: self.missing.update(newmissing) self.undecided.difference_update(newmissing) def addinfo(self, sample): """consume an iterable of (rev, known) tuples""" common = set() missing = set() for rev, known in sample: if known: common.add(rev) else: missing.add(rev) if common: self.addcommons(common) if missing: self.addmissings(missing) def hasinfo(self): """return True is we have any clue about the remote state""" return self._common.hasbases() def iscomplete(self): """True if all the necessary data have been gathered""" return self._undecided is not None and not self._undecided @property def undecided(self): if self._undecided is not None: return self._undecided self._undecided = set(self._common.missingancestors(self._targetheads)) return self._undecided def commonheads(self): """the heads of the known common set""" # heads(common) == heads(common.bases) since common represents # common.bases and all its ancestors return self._common.basesheads() def _parentsgetter(self): getrev = self._repo.changelog.index.__getitem__ def getparents(r): return getrev(r)[5:7] return getparents def _childrengetter(self): if self._childrenmap is not None: # During discovery, the `undecided` set keep shrinking. # Therefore, the map computed for an iteration N will be # valid for iteration N+1. Instead of computing the same # data over and over we cached it the first time. return self._childrenmap.__getitem__ # _updatesample() essentially does interaction over revisions to look # up their children. This lookup is expensive and doing it in a loop is # quadratic. We precompute the children for all relevant revisions and # make the lookup in _updatesample() a simple dict lookup. self._childrenmap = children = {} parentrevs = self._parentsgetter() revs = self.undecided for rev in sorted(revs): # Always ensure revision has an entry so we don't need to worry # about missing keys. children[rev] = [] for prev in parentrevs(rev): if prev == nullrev: continue c = children.get(prev) if c is not None: c.append(rev) return children.__getitem__ def takequicksample(self, headrevs, size): """takes a quick sample of size <size> It is meant for initial sampling and focuses on querying heads and close ancestors of heads. :headrevs: set of head revisions in local DAG to consider :size: the maximum size of the sample""" revs = self.undecided if len(revs) <= size: return list(revs) sample = set(self._repo.revs('heads(%ld)', revs)) if len(sample) >= size: return _limitsample(sample, size) _updatesample(None, headrevs, sample, self._parentsgetter(), quicksamplesize=size) return sample def takefullsample(self, headrevs, size): revs = self.undecided if len(revs) <= size: return list(revs) repo = self._repo sample = set(repo.revs('heads(%ld)', revs)) parentrevs = self._parentsgetter() # update from heads revsheads = sample.copy() _updatesample(revs, revsheads, sample, parentrevs) # update from roots revsroots = set(repo.revs('roots(%ld)', revs)) childrenrevs = self._childrengetter() _updatesample(revs, revsroots, sample, childrenrevs) assert sample sample = _limitsample(sample, size) if len(sample) < size: more = size - len(sample) sample.update(random.sample(list(revs - sample), more)) return sample def findcommonheads(ui, local, remote, initialsamplesize=100, fullsamplesize=200, abortwhenunrelated=True, ancestorsof=None): '''Return a tuple (common, anyincoming, remoteheads) used to identify missing nodes from or in remote. ''' start = util.timer() roundtrips = 0 cl = local.changelog clnode = cl.node clrev = cl.rev if ancestorsof is not None: ownheads = [clrev(n) for n in ancestorsof] else: ownheads = [rev for rev in cl.headrevs() if rev != nullrev] # early exit if we know all the specified remote heads already ui.debug("query 1; heads\n") roundtrips += 1 sample = _limitsample(ownheads, initialsamplesize) # indices between sample and externalized version must match sample = list(sample) with remote.commandexecutor() as e: fheads = e.callcommand('heads', {}) fknown = e.callcommand('known', { 'nodes': [clnode(r) for r in sample], }) srvheadhashes, yesno = fheads.result(), fknown.result() if cl.tip() == nullid: if srvheadhashes != [nullid]: return [nullid], True, srvheadhashes return [nullid], False, [] # start actual discovery (we note this before the next "if" for # compatibility reasons) ui.status(_("searching for changes\n")) knownsrvheads = [] # revnos of remote heads that are known locally for node in srvheadhashes: if node == nullid: continue try: knownsrvheads.append(clrev(node)) # Catches unknown and filtered nodes. except error.LookupError: continue if len(knownsrvheads) == len(srvheadhashes): ui.debug("all remote heads known locally\n") return srvheadhashes, False, srvheadhashes if len(sample) == len(ownheads) and all(yesno): ui.note(_("all local heads known remotely\n")) ownheadhashes = [clnode(r) for r in ownheads] return ownheadhashes, True, srvheadhashes # full blown discovery disco = partialdiscovery(local, ownheads) # treat remote heads (and maybe own heads) as a first implicit sample # response disco.addcommons(knownsrvheads) disco.addinfo(zip(sample, yesno)) full = False progress = ui.makeprogress(_('searching'), unit=_('queries')) while not disco.iscomplete(): if full or disco.hasinfo(): if full: ui.note(_("sampling from both directions\n")) else: ui.debug("taking initial sample\n") samplefunc = disco.takefullsample targetsize = fullsamplesize else: # use even cheaper initial sample ui.debug("taking quick initial sample\n") samplefunc = disco.takequicksample targetsize = initialsamplesize sample = samplefunc(ownheads, targetsize) roundtrips += 1 progress.update(roundtrips) ui.debug("query %i; still undecided: %i, sample size is: %i\n" % (roundtrips, len(disco.undecided), len(sample))) # indices between sample and externalized version must match sample = list(sample) with remote.commandexecutor() as e: yesno = e.callcommand('known', { 'nodes': [clnode(r) for r in sample], }).result() full = True disco.addinfo(zip(sample, yesno)) result = disco.commonheads() elapsed = util.timer() - start progress.complete() ui.debug("%d total queries in %.4fs\n" % (roundtrips, elapsed)) msg = ('found %d common and %d unknown server heads,' ' %d roundtrips in %.4fs\n') missing = set(result) - set(knownsrvheads) ui.log('discovery', msg, len(result), len(missing), roundtrips, elapsed) if not result and srvheadhashes != [nullid]: if abortwhenunrelated: raise error.Abort(_("repository is unrelated")) else: ui.warn(_("warning: repository is unrelated\n")) return ({nullid}, True, srvheadhashes,) anyincoming = (srvheadhashes != [nullid]) result = {clnode(r) for r in result} return result, anyincoming, srvheadhashes