# HG changeset patch
# User Gregory Szorc <gregory.sz...@gmail.com>
# Date 1480035243 28800
# Thu Nov 24 16:54:03 2016 -0800
# Node ID 328d95ac1fd128359a2665f2959e030ee8cce046
# Parent 4fffbdc2bca22e666482b55562c0e592c8a68027
repair: determine what upgrade will do
This commit is rather large. It started off as multiple commits
but I couldn't figure out a good way to split up the functionality
while still conveying the overall strategy. To the reviewer, I
apologize.
This commit introducts a ton of functionality around determining
how a repository can be upgraded.
The first code you'll see is related to repository requirements and
updates. There are no less than 5 functions returnings sets of
requirements that control upgrading. Why so many functions?
Mainly extensions. These would ideally be module variables. But
extensions will need to inject themselves into the upgrade process.
And if you are going to make 1 set extensible, you might as well
make them all extensible.
Astute readers will see that we don't support "manifestv2" and
"treemanifest" requirements in the upgrade mechanism. I don't have
a great answer for why other than this is a complex set of patches
and I don't want to deal with the complexity of these experimental
features just yet. We can teach the upgrade mechanism about them
later, once the basic upgrade mechanism is in place.
The "upgradefindimprovements" function introduces a mechanism to
return a list of improvements that can be made to a repository.
Each improvement is effectively an action that an upgrade will
perform. Associated with each of these improvements is metadata
that will be used to inform users what's wrong and what an
upgrade will do.
Each "improvement" is categorized as a "deficiency" or an
"optimization." TBH, I'm not thrilled about the terminology and
am receptive to constructive bikeshedding. The main difference
between a "deficiency" and an "optimization" is a deficiency
is always corrected (if it deviates from the current config) and
an "optimization" is an optional action that goes above and beyond
to improve the state of the repository (usually by requiring more
CPU during upgrade).
Our initial set of improvements identifies missing repository
requirements, a single, easily correctable problem with
changelog storage, and a set of "optimizations" related to delta
recalculation.
The main "upgraderepo" function glues all of this code together.
It verifies that the repository is capable of being upgraded by
looking at the state of current and proposed requirements and
every difference therein. It then queries for the list of
improvements and determines which of them will run based on the
current repository state and user arguments. A non-trivial amount
of code is required to print all the improvements and what
actions will be taken by an upgrade. Some of this is factored into
inline functions to facilitate use in a subsequent commit.
I went through numerous iterations of the output format before
settling on a ReST-inspired definition list format. (I used
bulleted lists in the first submission of this commit and could
not get it to format just right.) Even with the various iterations,
I'm still not super thrilled with the format. But, this is a debug*
command, so that should mean we can refine the output without BC
concerns.
Rounding out the code is a series of new tests.
diff --git a/mercurial/debugcommands.py b/mercurial/debugcommands.py
--- a/mercurial/debugcommands.py
+++ b/mercurial/debugcommands.py
@@ -34,6 +34,7 @@ from . import (
localrepo,
lock as lockmod,
pycompat,
+ repair,
revlog,
scmutil,
setdiscovery,
@@ -873,4 +874,4 @@ def debugupgraderepo(ui, repo, run=False
should complete almost instantaneously and the chances of a consumer being
unable to access the repository should be low.
"""
- raise error.Abort(_('not yet implemented'))
+ return repair.upgraderepo(ui, repo, run=run, optimize=optimize)
diff --git a/mercurial/repair.py b/mercurial/repair.py
--- a/mercurial/repair.py
+++ b/mercurial/repair.py
@@ -360,3 +360,417 @@ def deleteobsmarkers(obsstore, indices):
newobsstorefile.write(bytes)
newobsstorefile.close()
return n
+
+def upgraderequiredsourcerequirements(repo):
+ """Obtain requirements required to be present to upgrade a repo.
+
+ An upgrade will not be allowed if the repository doesn't have the
+ requirements returned by this function.
+ """
+ return set([
+ # Introduced in Mercurial 0.9.2.
+ 'revlogv1',
+ # Introduced in Mercurial 0.9.2.
+ 'store',
+ ])
+
+def upgradeblocksourcerequirements(repo):
+ """Obtain requirements that will prevent an upgrade from occurring.
+
+ An upgrade cannot be performed if the source repository contains a
+ requirements in the returned set.
+ """
+ return set([
+ # The upgrade code does not yet support these experimental features.
+ # This is an artificial limitation.
+ 'manifestv2',
+ 'treemanifest',
+ # This was a precursor to generaldelta and was never enabled by
default.
+ # It should (hopefully) not exist in the wild.
+ 'parentdelta',
+ # Upgrade should operate on the actual store, not the shared link.
+ 'shared',
+ ])
+
+def upgradesupportremovedrequirements(repo):
+ """Obtain requirements that can be removed during an upgrade.
+
+ If an upgrade were to create a repository that dropped a requirement,
+ the dropped requirement must appear in the returned set for the upgrade
+ to be allowed.
+ """
+ return set()
+
+def upgradesupporteddestrequirements(repo):
+ """Obtain requirements that upgrade supports in the destination.
+
+ If the result of the upgrade would create requirements not in this set,
+ the upgrade is disallowed.
+
+ Extensions should monkeypatch this to add their custom requirements.
+ """
+ return set([
+ 'dotencode',
+ 'fncache',
+ 'generaldelta',
+ 'revlogv1',
+ 'store',
+ ])
+
+def upgradeallowednewrequirements(repo):
+ """Obtain requirements that can be added to a repository during upgrade.
+
+ This is used to disallow proposed requirements from being added when
+ they weren't present before.
+
+ We use a list of allowed requirement additions instead of a list of known
+ bad additions because the whitelist approach is safer and will prevent
+ future, unknown requirements from accidentally being added.
+ """
+ return set([
+ 'dotencode',
+ 'fncache',
+ 'generaldelta',
+ ])
+
+def upgradefindimprovements(repo):
+ """Determine improvements that can be made to the repo during upgrade.
+
+ Returns a list of dicts describing repository deficiencies and
+ optimizations. Each dict value has the following keys:
+
+ name
+ Machine-readable string uniquely identifying this improvement. It
+ will be mapped to an action later in the upgrade process.
+
+ type
+ Either ``deficiency`` or ``optimization``. A deficiency is an obvious
+ problem. An ``optimization`` is an action (sometimes optional) that
+ can be taken to further improve the state of the repository.
+
+ description
+ Message intended for humans explaining the improvement in more detail,
+ including the implications of it. For ``deficiency`` types, should be
+ worded in the present tense. For ``optimization`` types, should be
+ worded in the future tense.
+
+ upgrademessage
+ Message intended for humans explaining what an upgrade addressing this
+ issue will do. Should be worded in the future tense.
+
+ fromdefault (``deficiency`` types only)
+ Boolean indicating whether the current (deficient) state deviates
+ from Mercurial's default configuration.
+
+ fromconfig (``deficiency`` types only)
+ Boolean indicating whether the current (deficient) state deviates
+ from the current Mercurial configuration.
+ """
+ # Avoid cycle: cmdutil -> repair -> localrepo -> cmdutil
+ from . import localrepo
+
+ newreporeqs = localrepo.newreporequirements(repo)
+
+ improvements = []
+
+ # We could detect lack of revlogv1 and store here, but they were added
+ # in 0.9.2 and we don't support upgrading repos without these
+ # requirements, so let's not bother.
+
+ if 'fncache' not in repo.requirements:
+ improvements.append({
+ 'name': 'fncache',
+ 'type': 'deficiency',
+ 'description':
+ _('long and reserved filenames may not work correctly; '
+ 'repository performance is sub-optimal'),
+ 'upgrademessage':
+ _('repository will be more resilient to storing certain '
+ 'paths and performance of certain operations should be '
+ 'improved'),
+ 'fromdefault': True,
+ 'fromconfig': 'fncache in newreporeqs',
+ })
+
+ if 'dotencode' not in repo.requirements:
+ improvements.append({
+ 'name': 'dotencode',
+ 'type': 'deficiency',
+ 'description':
+ _('storage of filenames beginning with a period or space may '
+ 'not work correctly'),
+ 'upgrademessage':
+ _('repository will be better able to store files beginning '
+ 'with a space or period'),
+ 'fromdefault': True,
+ 'fromconfig': 'dotencode' in newreporeqs,
+ })
+
+ if 'generaldelta' not in repo.requirements:
+ improvements.append({
+ 'name': 'generaldelta',
+ 'type': 'deficiency',
+ 'description':
+ _('deltas within internal storage are unable to choose optimal
'
+ 'revisions; repository is larger and slower than it could '
+ 'be; interaction with other repositories may require extra '
+ 'network and CPU resources, making "hg push" and "hg pull" '
+ 'slower'),
+ 'upgrademessage':
+ _('repository storage will be able to create optimal deltas; '
+ 'new repository data will be smaller and read times should '
+ 'decrease; interacting with other repositories using this '
+ 'storage model should require less network and CPU '
+ 'resources, making "hg push" and "hg pull" faster'),
+ 'fromdefault': True,
+ 'fromconfig': 'generaldelta' in newreporeqs,
+ })
+
+ # Mercurial 4.0 changed changelogs to not use delta chains. Search for
+ # changelogs with deltas.
+ cl = repo.changelog
+ for rev in cl:
+ chainbase = cl.chainbase(rev)
+ if chainbase != rev:
+ improvements.append({
+ 'name': 'removecldeltachain',
+ 'type': 'deficiency',
+ 'description':
+ _('changelog storage is using deltas instead of raw '
+ 'entries; changelog reading and any operation relying '
+ 'on changelog data are slower than they could be'),
+ 'upgrademessage':
+ _('changelog storage will be reformated to store raw '
+ 'entries; changelog reading will be faster; changelog '
+ 'size may be reduced'),
+ 'fromdefault': True,
+ 'fromconfig': True,
+ })
+ break
+
+ # Now for the optimizations.
+
+ # These are unconditionally added. There is logic later that figures out
+ # which ones to apply.
+
+ improvements.append({
+ 'name': 'redeltaparent',
+ 'type': 'optimization',
+ 'description':
+ _('deltas within internal storage will be recalculated to choose '
+ 'an optimal base revision where this was not already done; '
+ 'the size of the repository may shrink and various operations '
+ 'may become faster; the first time this optimization is '
+ 'performed could slow down upgrade execution considerably; '
+ 'subsequent invocations should not run noticeably slower'),
+ 'upgrademessage':
+ _('deltas within internal storage will choose a new base revision '
+ 'if needed'),
+ })
+
+ improvements.append({
+ 'name': 'redeltamultibase',
+ 'type': 'optimization',
+ 'description':
+ _('deltas within internal storage will be recalculated against '
+ 'multiple base revision and the smallest difference will be '
+ 'used; the size of the repository may shrink significantly when '
+ 'there are many merges; this optimization will slow down '
+ 'execution in proportion to the number of merges in the '
+ 'repository and the amount of files in the repository; this '
+ 'slow down should not be significant unless there are tens of '
+ 'thousands of files and thousands of merges'),
+ 'upgrademessage':
+ _('deltas within internal storage will choose an optimal delta by '
+ 'computing deltas against multiple parents; may slow down '
+ 'execution time significantly'),
+ })
+
+ improvements.append({
+ 'name': 'redeltaall',
+ 'type': 'optimization',
+ 'description':
+ _('deltas within internal storage will always be recalculated '
+ 'without reusing prior deltas; this will likely make execution '
+ 'run several times slower; this optimization is typically not '
+ 'needed'),
+ 'upgrademessage':
+ _('deltas within internal storage will be fully recomputed; '
+ 'this will likely drastically slow down execution time'),
+ })
+
+ return improvements
+
+def upgradedetermineactions(repo, improvements, sourcereqs, destreqs,
+ optimize):
+ """Determine upgrade actions that will be performed.
+
+ Given a list of improvements as returned by ``upgradefindimprovements``,
+ determine the list of upgrade actions that will be performed.
+
+ The role of this function is to filter improvements if needed, apply
+ recommended optimizations from the improvements list that make sense,
+ etc.
+
+ Returns a list of action names.
+ """
+ newactions = []
+
+ knownreqs = upgradesupporteddestrequirements(repo)
+
+ for i in improvements:
+ name = i['name']
+
+ # If the action is a requirement that doesn't show up in the
+ # destination requirements, prune the action.
+ if name in knownreqs and name not in destreqs:
+ continue
+
+ if i['type'] == 'deficiency':
+ newactions.append(name)
+
+ newactions.extend(o for o in sorted(optimize) if o not in newactions)
+
+ # FUTURE consider adding some optimizations here for certain transitions.
+ # e.g. adding generaldelta could schedule parent redeltas.
+
+ return newactions
+
+def upgraderepo(ui, repo, run=False, optimize=None):
+ """Upgrade a repository in place."""
+ # Avoid cycle: cmdutil -> repair -> localrepo -> cmdutil
+ from . import localrepo
+
+ optimize = set(optimize or [])
+
+ repo = repo.unfiltered()
+
+ # Ensure the repository can be upgraded.
+ missingreqs = upgraderequiredsourcerequirements(repo) - repo.requirements
+ if missingreqs:
+ raise error.Abort(_('cannot upgrade repository; requirement '
+ 'missing: %s') % _(', ').join(sorted(missingreqs)))
+
+ blockedreqs = upgradeblocksourcerequirements(repo) & repo.requirements
+ if blockedreqs:
+ raise error.Abort(_('cannot upgrade repository; unsupported source '
+ 'requirement: %s') %
+ _(', ').join(sorted(blockedreqs)))
+
+ # FUTURE there is potentially a need to control the wanted requirements via
+ # command arguments or via an extension hook point.
+ newreqs = localrepo.newreporequirements(repo)
+
+ noremovereqs = (repo.requirements - newreqs -
+ upgradesupportremovedrequirements(repo))
+ if noremovereqs:
+ raise error.Abort(_('cannot upgrade repository; requirement would be '
+ 'removed: %s') % _(',
').join(sorted(noremovereqs)))
+
+ noaddreqs = (newreqs - repo.requirements -
+ upgradeallowednewrequirements(repo))
+ if noaddreqs:
+ raise error.Abort(_('cannot upgrade repository; do not support adding '
+ 'requirement: %s') %
+ _(', ').join(sorted(noaddreqs)))
+
+ unsupportedreqs = newreqs - upgradesupporteddestrequirements(repo)
+ if unsupportedreqs:
+ raise error.Abort(_('cannot upgrade repository; do not support '
+ 'destination requirement: %s') %
+ _(', ').join(sorted(unsupportedreqs)))
+
+ # Find and validate all improvements that can be made.
+ improvements = upgradefindimprovements(repo)
+ for i in improvements:
+ if i['type'] not in ('deficiency', 'optimization'):
+ raise error.Abort(_('unexpected improvement type %s for %s') % (
+ i['type'], i['name']))
+
+ # Validate arguments.
+ unknownoptimize = optimize - set(i['name'] for i in improvements
+ if i['type'] == 'optimization')
+ if unknownoptimize:
+ raise error.Abort(_('unknown optimization action requested: %s') %
+ ', '.join(sorted(unknownoptimize)),
+ hint=_('run without arguments to see valid '
+ 'optimizations'))
+
+ actions = upgradedetermineactions(repo, improvements, repo.requirements,
+ newreqs, optimize)
+
+ def printrequirements():
+ ui.write(_('requirements\n'))
+ ui.write(_(' preserved: %s\n') %
+ _(', ').join(sorted(newreqs & repo.requirements)))
+
+ if repo.requirements - newreqs:
+ ui.write(_(' removed: %s\n') %
+ _(', ').join(sorted(repo.requirements - newreqs)))
+
+ if newreqs - repo.requirements:
+ ui.write(_(' added: %s\n') %
+ _(', ').join(sorted(newreqs - repo.requirements)))
+
+ ui.write('\n')
+
+ def printupgradeactions():
+ for action in actions:
+ for i in improvements:
+ if i['name'] == action:
+ ui.write('%s\n %s\n\n' %
+ (i['name'], i['upgrademessage']))
+
+ if not run:
+ fromdefault = []
+ fromconfig = []
+ optimizations = []
+
+ for i in improvements:
+ assert i['type'] in ('deficiency', 'optimization')
+ if i['type'] == 'deficiency':
+ if i['fromdefault']:
+ fromdefault.append(i)
+ if i['fromconfig']:
+ fromconfig.append(i)
+ else:
+ optimizations.append(i)
+
+ if fromdefault or fromconfig:
+ fromconfignames = set(x['name'] for x in fromconfig)
+ onlydefault = [i for i in fromdefault
+ if i['name'] not in fromconfignames]
+
+ if fromconfig:
+ ui.write(_('repository lacks features recommended by '
+ 'current config options:\n\n'))
+ for i in fromconfig:
+ ui.write('%s\n %s\n\n' % (i['name'], i['description']))
+
+ if onlydefault:
+ ui.write(_('repository lacks features used by the default '
+ 'config options:\n\n'))
+ for i in onlydefault:
+ ui.write('%s\n %s\n\n' % (i['name'], i['description']))
+
+ ui.write('\n')
+ else:
+ ui.write(_('(no feature deficiencies found in existing '
+ 'repository)\n'))
+
+ ui.write(_('performing an upgrade with "--run" will make the following
'
+ 'changes:\n\n'))
+
+ printrequirements()
+ printupgradeactions()
+
+ unusedoptimize = [i for i in improvements
+ if i['name'] not in actions and
+ i['type'] == 'optimization']
+ if unusedoptimize:
+ ui.write(_('additional optimizations are available by specifying '
+ '"--optimize <name>":\n\n'))
+ for i in unusedoptimize:
+ ui.write(_('%s\n %s\n\n') % (i['name'], i['description']))
+
+ return
diff --git a/tests/test-upgrade-repo.t b/tests/test-upgrade-repo.t
--- a/tests/test-upgrade-repo.t
+++ b/tests/test-upgrade-repo.t
@@ -1,5 +1,181 @@
+ $ cat >> $HGRCPATH << EOF
+ > [extensions]
+ > share =
+ > EOF
+
+store and revlogv1 are required in source
+
+ $ hg --config format.usestore=false init no-store
+ $ hg -R no-store debugupgraderepo
+ abort: cannot upgrade repository; requirement missing: store
+ [255]
+
+ $ hg init no-revlogv1
+ $ cat > no-revlogv1/.hg/requires << EOF
+ > dotencode
+ > fncache
+ > generaldelta
+ > store
+ > EOF
+
+ $ hg -R no-revlogv1 debugupgraderepo
+ abort: cannot upgrade repository; requirement missing: revlogv1
+ [255]
+
+Cannot upgrade shared repositories
+
+ $ hg init share-parent
+ $ hg -q share share-parent share-child
+
+ $ hg -R share-child debugupgraderepo
+ abort: cannot upgrade repository; unsupported source requirement: shared
+ [255]
+
+Do not yet support upgrading manifestv2 and treemanifest repos
+
+ $ hg --config experimental.manifestv2=true init manifestv2
+ $ hg -R manifestv2 debugupgraderepo
+ abort: cannot upgrade repository; unsupported source requirement: manifestv2
+ [255]
+
+ $ hg --config experimental.treemanifest=true init treemanifest
+ $ hg -R treemanifest debugupgraderepo
+ abort: cannot upgrade repository; unsupported source requirement:
treemanifest
+ [255]
+
+Cannot add manifestv2 or treemanifest requirement during upgrade
+
+ $ hg init disallowaddedreq
+ $ hg -R disallowaddedreq --config experimental.manifestv2=true --config
experimental.treemanifest=true debugupgraderepo
+ abort: cannot upgrade repository; do not support adding requirement:
manifestv2, treemanifest
+ [255]
+
+An upgrade of a repository created with recommended settings only suggests
optimizations
+
$ hg init empty
$ cd empty
$ hg debugupgraderepo
- abort: not yet implemented
- [255]
+ (no feature deficiencies found in existing repository)
+ performing an upgrade with "--run" will make the following changes:
+
+ requirements
+ preserved: dotencode, fncache, generaldelta, revlogv1, store
+
+ additional optimizations are available by specifying "--optimize <name>":
+
+ redeltaparent
+ deltas within internal storage will be recalculated to choose an optimal
base revision where this was not already done; the size of the repository may
shrink and various operations may become faster; the first time this
optimization is performed could slow down upgrade execution considerably;
subsequent invocations should not run noticeably slower
+
+ redeltamultibase
+ deltas within internal storage will be recalculated against multiple base
revision and the smallest difference will be used; the size of the repository
may shrink significantly when there are many merges; this optimization will
slow down execution in proportion to the number of merges in the repository and
the amount of files in the repository; this slow down should not be significant
unless there are tens of thousands of files and thousands of merges
+
+ redeltaall
+ deltas within internal storage will always be recalculated without
reusing prior deltas; this will likely make execution run several times slower;
this optimization is typically not needed
+
+
+--optimize can be used to add optimizations
+
+ $ hg debugupgrade --optimize redeltaparent
+ (no feature deficiencies found in existing repository)
+ performing an upgrade with "--run" will make the following changes:
+
+ requirements
+ preserved: dotencode, fncache, generaldelta, revlogv1, store
+
+ redeltaparent
+ deltas within internal storage will choose a new base revision if needed
+
+ additional optimizations are available by specifying "--optimize <name>":
+
+ redeltamultibase
+ deltas within internal storage will be recalculated against multiple base
revision and the smallest difference will be used; the size of the repository
may shrink significantly when there are many merges; this optimization will
slow down execution in proportion to the number of merges in the repository and
the amount of files in the repository; this slow down should not be significant
unless there are tens of thousands of files and thousands of merges
+
+ redeltaall
+ deltas within internal storage will always be recalculated without
reusing prior deltas; this will likely make execution run several times slower;
this optimization is typically not needed
+
+
+Various sub-optimal detections work
+
+ $ cat > .hg/requires << EOF
+ > revlogv1
+ > store
+ > EOF
+
+ $ hg debugupgraderepo
+ repository lacks features recommended by current config options:
+
+ fncache
+ long and reserved filenames may not work correctly; repository
performance is sub-optimal
+
+ dotencode
+ storage of filenames beginning with a period or space may not work
correctly
+
+ generaldelta
+ deltas within internal storage are unable to choose optimal revisions;
repository is larger and slower than it could be; interaction with other
repositories may require extra network and CPU resources, making "hg push" and
"hg pull" slower
+
+
+ performing an upgrade with "--run" will make the following changes:
+
+ requirements
+ preserved: revlogv1, store
+ added: dotencode, fncache, generaldelta
+
+ fncache
+ repository will be more resilient to storing certain paths and
performance of certain operations should be improved
+
+ dotencode
+ repository will be better able to store files beginning with a space or
period
+
+ generaldelta
+ repository storage will be able to create optimal deltas; new repository
data will be smaller and read times should decrease; interacting with other
repositories using this storage model should require less network and CPU
resources, making "hg push" and "hg pull" faster
+
+ additional optimizations are available by specifying "--optimize <name>":
+
+ redeltaparent
+ deltas within internal storage will be recalculated to choose an optimal
base revision where this was not already done; the size of the repository may
shrink and various operations may become faster; the first time this
optimization is performed could slow down upgrade execution considerably;
subsequent invocations should not run noticeably slower
+
+ redeltamultibase
+ deltas within internal storage will be recalculated against multiple base
revision and the smallest difference will be used; the size of the repository
may shrink significantly when there are many merges; this optimization will
slow down execution in proportion to the number of merges in the repository and
the amount of files in the repository; this slow down should not be significant
unless there are tens of thousands of files and thousands of merges
+
+ redeltaall
+ deltas within internal storage will always be recalculated without
reusing prior deltas; this will likely make execution run several times slower;
this optimization is typically not needed
+
+
+ $ hg --config format.dotencode=false debugupgraderepo
+ repository lacks features recommended by current config options:
+
+ fncache
+ long and reserved filenames may not work correctly; repository
performance is sub-optimal
+
+ generaldelta
+ deltas within internal storage are unable to choose optimal revisions;
repository is larger and slower than it could be; interaction with other
repositories may require extra network and CPU resources, making "hg push" and
"hg pull" slower
+
+ repository lacks features used by the default config options:
+
+ dotencode
+ storage of filenames beginning with a period or space may not work
correctly
+
+
+ performing an upgrade with "--run" will make the following changes:
+
+ requirements
+ preserved: revlogv1, store
+ added: fncache, generaldelta
+
+ fncache
+ repository will be more resilient to storing certain paths and
performance of certain operations should be improved
+
+ generaldelta
+ repository storage will be able to create optimal deltas; new repository
data will be smaller and read times should decrease; interacting with other
repositories using this storage model should require less network and CPU
resources, making "hg push" and "hg pull" faster
+
+ additional optimizations are available by specifying "--optimize <name>":
+
+ redeltaparent
+ deltas within internal storage will be recalculated to choose an optimal
base revision where this was not already done; the size of the repository may
shrink and various operations may become faster; the first time this
optimization is performed could slow down upgrade execution considerably;
subsequent invocations should not run noticeably slower
+
+ redeltamultibase
+ deltas within internal storage will be recalculated against multiple base
revision and the smallest difference will be used; the size of the repository
may shrink significantly when there are many merges; this optimization will
slow down execution in proportion to the number of merges in the repository and
the amount of files in the repository; this slow down should not be significant
unless there are tens of thousands of files and thousands of merges
+
+ redeltaall
+ deltas within internal storage will always be recalculated without
reusing prior deltas; this will likely make execution run several times slower;
this optimization is typically not needed
+
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