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changegroup: remove reordering control (BC)...
changegroup: remove reordering control (BC) This logic - including the experimental bundle.reorder option - was originally added in a8e3931e3fb5 in 2011 and then later ported to changegroup.py. The intent of this option and associated logic is to control the ordering of revisions in deltagroups in changegroups. At the time it was implemented, only changegroup version 1 existed and generaldelta revlogs were just coming into the world. Changegroup version 1 requires that deltas be made against the last revision sent over the wire. Used with generaldelta, this created an impedance mismatch of sorts and resulted in changegroup producers spending a lot of time recomputing deltas. Revision reordering was introduced so outgoing revisions would be sent in "generaldelta order" and producers would be able to reuse internal deltas from storage. Later on, we introduced changegroup version 2. It supported denoting which revision a delta was against. So we no longer needed to sort outgoing revisions to ensure optimal delta generation from the producer. So, subsequent changegroup versions disabled reordering. We also later made the changelog not store deltas by default. And we also made the changelog send out deltas in storage order. Why we do this for changelog, I'm not sure. Maybe we want to preserve revision order across clones? It doesn't really matter for this commit. Fast forward to 2018. We want to abstract storage backends. And having changegroup code require knowledge about how deltas are stored internally interferes with that goal. This commit removes reordering control from changegroup generation. After this commit, the reordering behavior is: * The changelog is always sent out in storage order (no behavior change). * Non-changelog generaldelta revlogs are reordered to always be in DAG topological order (previously, generaldelta revlogs would be emitted in storage order for version 2 and 3 changegroups). * Non-changelog non-generaldelta revlogs are sent in storage order (no behavior change). * There exists no config option to override behavior. The big difference here is that generaldelta revlogs now *always* have their revisions sorted in DAG order before going out over the wire. This behavior was previously only done for changegroup version 1. Version 2 and version 3 changegroups disabled reordering because the interchange format supported encoding arbitrary delta parents, so reordering wasn't strictly necessary. I can think of a few significant implications for this change. Because changegroup receivers will now see non-changelog revisions in DAG order instead of storage order, the internal storage order of manifests and files may differ substantially between producer and consumer. I don't think this matters that much, since the storage order of manifests and files is largely hidden from users. Only the storage order of changelog matters (because `hg log` shows the changelog in storage order). I don't think there should be any controversy here. The reordering of revisions has implications for changegroup producers. Previously, generaldelta revlogs would be emitted in storage order. And in the common case, the internally-stored delta could effectively be copied from disk into the deltagroup delta. This meant that emitting delta groups for generaldelta revlogs would be mostly linear read I/O. This is desirable for performance. With us now reordering generaldelta revlog revisions in DAG order, the read operations may use more random I/O instead of sequential I/O. This could result in performance loss. But with the prevalence of SSDs and fast random I/O, I'm not too worried. (Note: the optimal emission order for revlogs is actually delta encoding order. But the changegroup code wasn't doing that before or after this change. We could potentially implement that in a later commit.) Changegroups in DAG order will have implications for receivers. Previously, receiving storage order might mean seeing a number of interleaved branches. This would mean long delta chains, sparse I/O, and possibly more fulltext revisions instead of deltas, blowing up storage storage. (This is the same set of problems that sparse revlogs aims to address.) With the producer now sending revisions in DAG order, the receiver also stores revisions in DAG order. That means revisions for the same DAG branch are all grouped together. And this should yield better storage outcomes. In other words, sending the reordered changegroup allows the receiver to have better storage order and for the producer to not propagate its (possibly sub-optimal) internal storage order. On the mozilla-unified repository, this change influences bundle generation: $ hg bundle -t none-v2 -a before: time: real 355.680 secs (user 256.790+0.000 sys 16.820+0.000) after: time: real 382.950 secs (user 281.700+0.000 sys 17.690+0.000) before: 7,150,228,967 bytes (uncompressed) after: 7,041,556,273 bytes (uncompressed) before: 1,669,063,234 bytes (zstd l=3) after: 1,628,598,830 bytes (zstd l=3) $ hg unbundle before: time: real 511.910 secs (user 466.750+0.000 sys 32.680+0.000) after: time: real 487.790 secs (user 443.940+0.000 sys 30.840+0.000) 00manifest.d size: source: 274,924,292 bytes before: 304,741,626 bytes after: 245,252,087 bytes .hg/store total file size: source: 2,649,133,490 before: 2,680,888,130 after: 2,627,875,673 We see the bundle size drop. That's probably because if a revlog internally isn't storing a delta, it will choose to delta against the last emitted revision. And on repos with interleaved branches (like mozilla-unified), the previous revision could be an unrelated branch and therefore be a large delta. But with this patch, the previous revision is likely p1 or p2 and a delta should be small. We also see the manifest size drop by ~50 MB. It's worth noting that the manifest actually *increased* in size by ~25 MB in the old strategy and decreased ~25 MB from its source in the new strategy. Again, my explanation for this is that the DAG ordering in the changegroup is resulting in better grouping of revisions in the receiver, which results in more compact delta chains and higher storage efficiency. Unbundle time also dropped. I suspect this is due to the revlog having to work less to compute deltas since the incoming deltas are more optimal. i.e. the receiver spends less time resolving fulltext revisions as incoming deltas bounce around between DAG branches and delta chains. We also see bundle generation time increase. This is not desirable. However, the regression is only significant on the original repository: if we generate a bundle from the repository created from the new, always reordered bundles, we're close to baseline (if not at it with expected noise): $ hg bundle -t none-v2 -a before (original): time: real 355.680 secs (user 256.790+0.000 sys 16.820+0.000) after (original): time: real 382.950 secs (user 281.700+0.000 sys 17.690+0.000) after (new repo): time: real 362.280 secs (user 260.300+0.000 sys 17.700+0.000) This regression is a bit worrying because it will impact serving canonical repositories (that don't have optimal internal storage unless they are reordered - possibly as part of running `hg debugupgraderepo`). However, this regression will only be noticed by very large changegroups. And I'm guessing/hoping that any repository that large is using clonebundles to mitigate server load. Again, sending DAG order isn't the optimal send order for servers: sending in storage-delta order is. But in order to enable storage-optimal send order, we'll need a storage API that handles sorting. Future commits will introduce such an API. Differential Revision: https://phab.mercurial-scm.org/D4721

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__init__.py
107 lines | 3.0 KiB | text/x-python | PythonLexer
Eric Hopper
Fixing up comment headers for split up code.
r2391 # hgweb/__init__.py - web interface to a mercurial repository
Eric Hopper
Moving hgweb.py into it's own module in preparation for breaking it up.
r2311 #
# Copyright 21 May 2005 - (c) 2005 Jake Edge <jake@edge2.net>
# Copyright 2005 Matt Mackall <mpm@selenic.com>
#
Martin Geisler
updated license to be explicit about GPL version 2
r8225 # This software may be used and distributed according to the terms of the
Matt Mackall
Update license to GPLv2+
r10263 # GNU General Public License version 2 or any later version.
Eric Hopper
Moving hgweb.py into it's own module in preparation for breaking it up.
r2311
Yuya Nishihara
hgweb: use absolute_import
r27046 from __future__ import absolute_import
Matt Mackall
hgweb: make hgweb.hgweb a unified interface to hgweb/hgwebdir
r10996 import os
Yuya Nishihara
hgweb: use absolute_import
r27046
Yuya Nishihara
hgweb: move httpservice object from commands module...
r27138 from ..i18n import _
from .. import (
Yuya Nishihara
hgweb: extract factory function of httpservice object...
r27139 error,
Augie Fackler
hgweb: rewrite most obviously-native-strings to be native strings...
r34705 pycompat,
Yuya Nishihara
procutil: bulk-replace function calls to point to new module
r37138 )
from ..utils import (
procutil,
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hgweb: move httpservice object from commands module...
r27138 )
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hgweb: use absolute_import
r27046 from . import (
hgweb_mod,
hgwebdir_mod,
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hgweb: move httpservice object from commands module...
r27138 server,
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hgweb: use absolute_import
r27046 )
Matt Mackall
Replace demandload with new demandimport
r3877
Matt Mackall
hgweb: make hgweb.hgweb a unified interface to hgweb/hgwebdir
r10996 def hgweb(config, name=None, baseui=None):
'''create an hgweb wsgi object
config can be one of:
- repo object (single repo view)
- path to repo (single repo view)
- path to config file (multi-repo view)
- dict of virtual:real pairs (multi-repo view)
- list of virtual:real tuples (multi-repo view)
'''
Augie Fackler
hgweb: inform hgweb.hgweb() entrypoint that paths should be bytes...
r37763 if ((isinstance(config, bytes) and not os.path.isdir(config)) or
Matt Mackall
hgweb: make hgweb.hgweb a unified interface to hgweb/hgwebdir
r10996 isinstance(config, dict) or isinstance(config, list)):
# create a multi-dir interface
return hgwebdir_mod.hgwebdir(config, baseui=baseui)
return hgweb_mod.hgweb(config, name=name, baseui=baseui)
Matt Mackall
Replace demandload with new demandimport
r3877
Matt Mackall
hgweb: make top-level prototypes mirror their callees
r10992 def hgwebdir(config, baseui=None):
return hgwebdir_mod.hgwebdir(config, baseui=baseui)
Matt Mackall
Replace demandload with new demandimport
r3877
Yuya Nishihara
hgweb: move httpservice object from commands module...
r27138 class httpservice(object):
def __init__(self, ui, app, opts):
self.ui = ui
self.app = app
self.opts = opts
def init(self):
Yuya Nishihara
procutil: bulk-replace function calls to point to new module
r37138 procutil.setsignalhandler()
Yuya Nishihara
hgweb: move httpservice object from commands module...
r27138 self.httpd = server.create_server(self.ui, self.app)
Nicola Spanti
serve: add option print-url...
r38196 if (self.opts['port'] and
not self.ui.verbose and
not self.opts['print_url']):
Yuya Nishihara
hgweb: move httpservice object from commands module...
r27138 return
if self.httpd.prefix:
prefix = self.httpd.prefix.strip('/') + '/'
else:
prefix = ''
Augie Fackler
hgweb: rewrite most obviously-native-strings to be native strings...
r34705 port = r':%d' % self.httpd.port
if port == r':80':
port = r''
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hgweb: move httpservice object from commands module...
r27138
bindaddr = self.httpd.addr
Augie Fackler
hgweb: rewrite most obviously-native-strings to be native strings...
r34705 if bindaddr == r'0.0.0.0':
bindaddr = r'*'
elif r':' in bindaddr: # IPv6
bindaddr = r'[%s]' % bindaddr
Yuya Nishihara
hgweb: move httpservice object from commands module...
r27138
fqaddr = self.httpd.fqaddr
Augie Fackler
hgweb: rewrite most obviously-native-strings to be native strings...
r34705 if r':' in fqaddr:
fqaddr = r'[%s]' % fqaddr
Nicola Spanti
serve: add option print-url...
r38196
url = 'http://%s%s/%s' % (
pycompat.sysbytes(fqaddr), pycompat.sysbytes(port), prefix)
if self.opts['print_url']:
self.ui.write('%s\n' % url)
Yuya Nishihara
hgweb: move httpservice object from commands module...
r27138 else:
Nicola Spanti
serve: add option print-url...
r38196 if self.opts['port']:
write = self.ui.status
else:
write = self.ui.write
write(_('listening at %s (bound to %s:%d)\n') %
(url, pycompat.sysbytes(bindaddr), self.httpd.port))
Yuya Nishihara
hgweb: move httpservice object from commands module...
r27138 self.ui.flush() # avoid buffering of status message
def run(self):
self.httpd.serve_forever()
Yuya Nishihara
hgweb: extract factory function of httpservice object...
r27139
Yuya Nishihara
hgweb: extract app factory...
r30508 def createapp(baseui, repo, webconf):
Yuya Nishihara
hgweb: eliminate duck-typing to select hgweb or hgwebdir by command option...
r27181 if webconf:
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hgweb: extract app factory...
r30508 return hgwebdir_mod.hgwebdir(webconf, baseui=baseui)
Yuya Nishihara
hgweb: eliminate duck-typing to select hgweb or hgwebdir by command option...
r27181 else:
Yuya Nishihara
hgweb: extract factory function of httpservice object...
r27139 if not repo:
raise error.RepoError(_("there is no Mercurial repository"
" here (.hg not found)"))
Yuya Nishihara
hgweb: extract app factory...
r30508 return hgweb_mod.hgweb(repo, baseui=baseui)