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Differential D533

effectflag: store an empty effect flag for the moment
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Authored by lothiraldan on Aug 28 2017, 7:02 AM.

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rHG014d467f9d08: effectflag: store an empty effect flag for the moment
Summary

The idea behind effect flag is to store additional information in obs-markers
about what changed between a changeset and its successor(s). It's a low-level
information that comes without guarantees.

This information can be computed a posteriori, but only if we have all
changesets locally. This is not the case with distributed workflows where you
work with several people or on several computers (eg: laptop + build server).

Storing the effect-flag as a bitfield has several advantages:

  • It's compact, we are using one byte per obs-marker at most for the effect- flag.
  • It's compoundable, the obsfate log approach needs to display evolve history that could spans several obs-markers. Computing the effect-flag between a changeset and its grand-grand-grand-successor is simple thanks to the bitfield.

The effect-flag design has also some limitations:

  • Evolving a changeset and reverting these changes just after would lead to two obs-markers with the same effect-flag without information that the first and third changesets are the same.

The effect-flag current design is a trade-off between compactness and
usefulness.

Storing this information helps commands to display a more complete and
understandable evolve history. For example, obslog (an Evolve command) use it
to improve its output:

x 62206adfd571 (34302) obscache: skip updating outdated obscache...

rewritten(parent) by Matthieu Laneuville <matthieu.laneuville@octobus...
rewritten(content) by Boris Feld <boris.feld@octobus.net>

The effect flag is stored in obs-markers metadata while we iterate on the
information we want to store. We plan to extend the existing obsmarkers
bit-field when the effect flag design will be stabilized.

It's different from the CommitCustody concept, effect-flag are not signed and
can be forged. It's also different from the operation metadata as the command
name (for example: amend) could alter a changeset in different ways (changing
the content with hg amend, changing the description with hg amend -e, changing
the user with hg amend -U). Also it's compatible with every custom command
that writes obs-markers without needing to be updated.

The effect-flag is placed behind an experimental flag set to off by default.

Hook the saving of effect flag in create markers, but store only an empty one
for the moment, I will refine the values in effect flag in following patches.

For more information, see:

https://www.mercurial-scm.org/wiki/ChangesetEvolutionDevel#Record_types_of_operation

Diff Detail

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rHG Mercurial
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Event Timeline

lothiraldan created this revision.Aug 28 2017, 7:02 AM
lothiraldan updated this revision to Diff 2104.Sep 27 2017, 4:07 AM
lothiraldan edited the summary of this revision. (Show Details)Oct 1 2017, 9:44 AM
lothiraldan updated this revision to Diff 2286.
Closed by commit rHG014d467f9d08: effectflag: store an empty effect flag for the moment (authored by lothiraldan). · Explain WhyOct 1 2017, 5:20 PM
This revision was automatically updated to reflect the committed changes.

Revision Contents
Changeset List

PathPackages
Mmercurial/obsolete.py (12 lines)
Mmercurial/obsutil.py (13 lines)

Diff 2304

mercurial/obsolete.py

metadata['user'] = repo.ui.username() metadata['user'] = repo.ui.username()
# Operation metadata handling # Operation metadata handling
useoperation = repo.ui.configbool('experimental', useoperation = repo.ui.configbool('experimental',
'stabilization.track-operation') 'stabilization.track-operation')
if useoperation and operation: if useoperation and operation:
metadata['operation'] = operation metadata['operation'] = operation
# Effect flag metadata handling
saveeffectflag = repo.ui.configbool('experimental',
'effect-flags',
False)
tr = repo.transaction('add-obsolescence-marker') tr = repo.transaction('add-obsolescence-marker')
try: try:
markerargs = [] markerargs = []
for rel in relations: for rel in relations:
prec = rel[0] prec = rel[0]
sucs = rel[1] sucs = rel[1]
localmetadata = metadata.copy() localmetadata = metadata.copy()
if 2 < len(rel): if 2 < len(rel):
localmetadata.update(rel[2]) localmetadata.update(rel[2])
if not prec.mutable(): if not prec.mutable():
raise error.Abort(_("cannot obsolete public changeset: %s") raise error.Abort(_("cannot obsolete public changeset: %s")
% prec, % prec,
hint="see 'hg help phases' for details") hint="see 'hg help phases' for details")
nprec = prec.node() nprec = prec.node()
nsucs = tuple(s.node() for s in sucs) nsucs = tuple(s.node() for s in sucs)
npare = None npare = None
if not nsucs: if not nsucs:
npare = tuple(p.node() for p in prec.parents()) npare = tuple(p.node() for p in prec.parents())
if nprec in nsucs: if nprec in nsucs:
raise error.Abort(_("changeset %s cannot obsolete itself") raise error.Abort(_("changeset %s cannot obsolete itself")
% prec) % prec)
# Effect flag can be different by relation
if saveeffectflag:
# The effect flag is saved in a versioned field name for future
# evolution
effectflag = obsutil.geteffectflag(rel)
localmetadata[obsutil.EFFECTFLAGFIELD] = "%d" % effectflag
# Creating the marker causes the hidden cache to become invalid, # Creating the marker causes the hidden cache to become invalid,
# which causes recomputation when we ask for prec.parents() above. # which causes recomputation when we ask for prec.parents() above.
# Resulting in n^2 behavior. So let's prepare all of the args # Resulting in n^2 behavior. So let's prepare all of the args
# first, then create the markers. # first, then create the markers.
markerargs.append((nprec, nsucs, npare, localmetadata)) markerargs.append((nprec, nsucs, npare, localmetadata))
for args in markerargs: for args in markerargs:
nprec, nsucs, npare, localmetadata = args nprec, nsucs, npare, localmetadata = args
repo.obsstore.create(tr, nprec, nsucs, flag, parents=npare, repo.obsstore.create(tr, nprec, nsucs, flag, parents=npare,
date=date, metadata=localmetadata, date=date, metadata=localmetadata,
ui=repo.ui) ui=repo.ui)
repo.filteredrevcache.clear() repo.filteredrevcache.clear()
tr.close() tr.close()
finally: finally:
tr.release() tr.release()

mercurial/obsutil.py

plen = len(foreground) plen = len(foreground)
succs = set(c.node() for c in foreground) succs = set(c.node() for c in foreground)
mutable = [c.node() for c in foreground if c.mutable()] mutable = [c.node() for c in foreground if c.mutable()]
succs.update(allsuccessors(repo.obsstore, mutable)) succs.update(allsuccessors(repo.obsstore, mutable))
known = (n for n in succs if n in nm) known = (n for n in succs if n in nm)
foreground = set(repo.set('%ln::', known)) foreground = set(repo.set('%ln::', known))
return set(c.node() for c in foreground) return set(c.node() for c in foreground)
# logic around storing and using effect flags
EFFECTFLAGFIELD = "ef1"
def geteffectflag(relation):
""" From an obs-marker relation, compute what changed between the
predecessor and the successor.
"""
effects = 0
source = relation[0]
return effects
def getobsoleted(repo, tr): def getobsoleted(repo, tr):
"""return the set of pre-existing revisions obsoleted by a transaction""" """return the set of pre-existing revisions obsoleted by a transaction"""
torev = repo.unfiltered().changelog.nodemap.get torev = repo.unfiltered().changelog.nodemap.get
phase = repo._phasecache.phase phase = repo._phasecache.phase
succsmarkers = repo.obsstore.successors.get succsmarkers = repo.obsstore.successors.get
public = phases.public public = phases.public
addedmarkers = tr.changes.get('obsmarkers') addedmarkers = tr.changes.get('obsmarkers')
addedrevs = tr.changes.get('revs') addedrevs = tr.changes.get('revs')