view tests/test-rebase-dest.t @ 47802:de2e04fe4897

hgwebdir: avoid systematic full garbage collection

Forcing a systematic full garbage collection upon each request
can serioulsy harm performance. This is reported as
https://bz.mercurial-scm.org/show_bug.cgi?id=6075

With this change we're performing the full collection according
to a new setting, `experimental.web.full-garbage-collection-rate`.
The default value is 1, which doesn't change the behavior and will
allow us to test on real use cases. If the value is 0, no full garbage
collection occurs.

Regardless of the value of the setting, a partial garbage collection
still occurs upon each request (not attempting to collect objects from
the oldest generation). This should be enough to take care of
reference cycles that have been created by the last request
(assessment of this requires changing the setting, not to be 1).

In my experience chasing memory leaks in Mercurial servers,
the full collection never reclaimed any memory, but this is with
Python 3 and biased towards small repositories.

On the other hand, as explained in the Python developer docs [1],
frequent full collections are very harmful in terms of performance if
lots of objects survive the collection, and hence stay in the
oldest generation. Note that `gc.collect()` is indeed trying to
collect the oldest generation [2]. This happens usually in two cases:

- unwanted lingering objects (i.e., an actual memory leak that
  the GC cannot do anything about). Sadly, we have lots of those
  these days.
- desireable long-term objects, typically in caches (not inner caches
  carried by repositories, which should be collected with them). This
  is a subject of interest for the Heptapod project.

In short, the flat rate that this change still permits is
probably a bad idea in most cases, and the default value can
be tweaked later on (or even be set to 0) according to experiments
in the wild.

The test is inspired from test-hgwebdir-paths.py

[1] https://devguide.python.org/garbage_collector/#collecting-the-oldest-generation
[2] https://docs.python.org/3/library/gc.html#gc.collect

Differential Revision: https://phab.mercurial-scm.org/D11204

Require a destination
  $ cat >> $HGRCPATH <<EOF
  > [extensions]
  > rebase =
  > [commands]
  > rebase.requiredest = True
  > EOF
  $ hg init repo
  $ cd repo
  $ echo a >> a
  $ hg commit -qAm aa
  $ echo b >> b
  $ hg commit -qAm bb
  $ hg up ".^"
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
  $ echo c >> c
  $ hg commit -qAm cc
  $ hg rebase
  abort: you must specify a destination
  (use: hg rebase -d REV)
  [10]
  $ hg rebase -d 1
  rebasing 2:5db65b93a12b tip "cc"
  saved backup bundle to $TESTTMP/repo/.hg/strip-backup/5db65b93a12b-4fb789ec-rebase.hg
  $ hg rebase -d 0 -r . -q
  $ HGPLAIN=1 hg rebase
  rebasing 2:889b0bc6a730 tip "cc"
  saved backup bundle to $TESTTMP/repo/.hg/strip-backup/889b0bc6a730-41ec4f81-rebase.hg
  $ hg rebase -d 0 -r . -q
  $ hg --config commands.rebase.requiredest=False rebase
  rebasing 2:279de9495438 tip "cc"
  saved backup bundle to $TESTTMP/repo/.hg/strip-backup/279de9495438-ab0a5128-rebase.hg

Requiring dest should not break continue or other rebase options
  $ hg up 1 -q
  $ echo d >> c
  $ hg commit -qAm dc
  $ hg log -G -T '{rev} {desc}'
  @  3 dc
  |
  | o  2 cc
  |/
  o  1 bb
  |
  o  0 aa
  
  $ hg rebase -d 2
  rebasing 3:0537f6b50def tip "dc"
  merging c
  warning: conflicts while merging c! (edit, then use 'hg resolve --mark')
  unresolved conflicts (see 'hg resolve', then 'hg rebase --continue')
  [240]
  $ echo d > c
  $ hg resolve --mark --all
  (no more unresolved files)
  continue: hg rebase --continue
  $ hg rebase --continue
  rebasing 3:0537f6b50def tip "dc"
  saved backup bundle to $TESTTMP/repo/.hg/strip-backup/0537f6b50def-be4c7386-rebase.hg

  $ cd ..

Check rebase.requiredest interaction with pull --rebase
  $ hg clone repo clone
  updating to branch default
  3 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ cd repo
  $ echo e > e
  $ hg commit -qAm ee
  $ cd ..
  $ cd clone
  $ echo f > f
  $ hg commit -qAm ff
  $ hg pull --rebase
  abort: rebase destination required by configuration
  (use hg pull followed by hg rebase -d DEST)
  [10]

Setup rebase with multiple destinations

  $ cd $TESTTMP

  $ cat >> $TESTTMP/maprevset.py <<EOF
  > from __future__ import absolute_import
  > from mercurial import registrar, revset, revsetlang, smartset
  > revsetpredicate = registrar.revsetpredicate()
  > cache = {}
  > @revsetpredicate(b'map')
  > def map(repo, subset, x):
  >     """(set, mapping)"""
  >     setarg, maparg = revsetlang.getargs(x, 2, 2, b'')
  >     rset = revset.getset(repo, smartset.fullreposet(repo), setarg)
  >     mapstr = revsetlang.getstring(maparg, b'')
  >     map = dict(a.split(b':') for a in mapstr.split(b','))
  >     rev = rset.first()
  >     desc = repo[rev].description()
  >     newdesc = map.get(desc)
  >     if newdesc == b'null':
  >         revs = [-1]
  >     else:
  >         query = revsetlang.formatspec(b'desc(%s)', newdesc)
  >         revs = repo.revs(query)
  >     return smartset.baseset(revs)
  > EOF

  $ cat >> $HGRCPATH <<EOF
  > [ui]
  > allowemptycommit=1
  > [extensions]
  > drawdag=$TESTDIR/drawdag.py
  > [phases]
  > publish=False
  > [alias]
  > tglog = log -G --template "{rev}: {node|short} {desc} {instabilities}" -r 'sort(all(), topo)'
  > [extensions]
  > maprevset=$TESTTMP/maprevset.py
  > [experimental]
  > evolution=true
  > EOF

  $ rebasewithdag() {
  >   N=`"$PYTHON" -c "print($N+1)"`
  >   hg init repo$N && cd repo$N
  >   hg debugdrawdag
  >   hg rebase "$@" > _rebasetmp
  >   r=$?
  >   grep -v 'saved backup bundle' _rebasetmp
  >   [ $r -eq 0 ] && rm -f .hg/localtags && hg tglog
  >   cd ..
  >   return $r
  > }

Destination resolves to an empty set:

  $ rebasewithdag -s B -d 'SRC - SRC' <<'EOS'
  > C
  > |
  > B
  > |
  > A
  > EOS
  nothing to rebase - empty destination
  [1]

Multiple destinations and --collapse are not compatible:

  $ rebasewithdag -s C+E -d 'SRC^^' --collapse <<'EOS'
  > C F
  > | |
  > B E
  > | |
  > A D
  > EOS
  abort: --collapse does not work with multiple destinations
  [10]

Multiple destinations cannot be used with --base:

  $ rebasewithdag -b B -b E -d 'SRC^^' --collapse <<'EOS'
  > B E
  > | |
  > A D
  > EOS
  abort: unknown revision 'SRC'
  [255]

Rebase to null should work:

  $ rebasewithdag -r A+C+D -d 'null' <<'EOS'
  > C D
  > | |
  > A B
  > EOS
  already rebased 0:426bada5c675 A "A"
  already rebased 2:dc0947a82db8 C "C"
  rebasing 3:004dc1679908 D tip "D"
  o  4: d8d8601abd5e D
  
  o  2: dc0947a82db8 C
  |
  | o  1: fc2b737bb2e5 B
  |
  o  0: 426bada5c675 A
  
Destination resolves to multiple changesets:

  $ rebasewithdag -s B -d 'ALLSRC+SRC' <<'EOS'
  > C
  > |
  > B
  > |
  > Z
  > EOS
  abort: rebase destination for f0a671a46792 is not unique
  [10]

Destination is an ancestor of source:

  $ rebasewithdag -s B -d 'SRC' <<'EOS'
  > C
  > |
  > B
  > |
  > Z
  > EOS
  abort: source and destination form a cycle
  [10]

BUG: cycles aren't flagged correctly when --dry-run is set:
  $ rebasewithdag -s B -d 'SRC' --dry-run <<'EOS'
  > C
  > |
  > B
  > |
  > Z
  > EOS
  abort: source and destination form a cycle
  starting dry-run rebase; repository will not be changed
  [10]

Switch roots:

  $ rebasewithdag -s 'all() - roots(all())' -d 'roots(all()) - ::SRC' <<'EOS'
  > C  F
  > |  |
  > B  E
  > |  |
  > A  D
  > EOS
  rebasing 2:112478962961 B "B"
  rebasing 4:26805aba1e60 C "C"
  rebasing 3:cd488e83d208 E "E"
  rebasing 5:0069ba24938a F tip "F"
  o  9: d150ff263fc8 F
  |
  o  8: 66f30a1a2eab E
  |
  | o  7: 93db94ffae0e C
  | |
  | o  6: d0071c3b0c88 B
  | |
  | o  1: 058c1e1fb10a D
  |
  o  0: 426bada5c675 A
  
Different destinations for merge changesets with a same root:

  $ rebasewithdag -s B -d '((parents(SRC)-B-A)::) - (::ALLSRC)' <<'EOS'
  > C G
  > |\|
  > | F
  > |
  > B E
  > |\|
  > A D
  > EOS
  rebasing 3:a4256619d830 B "B"
  rebasing 6:8e139e245220 C tip "C"
  o    8: d7d1169e9b1c C
  |\
  | o    7: 2ed0c8546285 B
  | |\
  o | |  5: 8fdb2c1feb20 G
  | | |
  | | o  4: cd488e83d208 E
  | | |
  o | |  2: a6661b868de9 F
   / /
  | o  1: 058c1e1fb10a D
  |
  o  0: 426bada5c675 A
  
Move to a previous parent:

  $ rebasewithdag -s E -s F -s G -d 'SRC^^' <<'EOS'
  >     H
  >     |
  >   D G
  >   |/
  >   C F
  >   |/
  >   B E  # E will be ignored, since E^^ is empty
  >   |/
  >   A
  > EOS
  rebasing 4:33441538d4aa F "F"
  rebasing 6:cf43ad9da869 G "G"
  rebasing 7:eef94f3b5f03 H tip "H"
  o  10: b3d84c6666cf H
  |
  | o  5: f585351a92f8 D
  |/
  o  3: 26805aba1e60 C
  |
  | o  9: f7c28a1a15e2 G
  |/
  o  1: 112478962961 B
  |
  | o  8: 02aa697facf7 F
  |/
  | o  2: 7fb047a69f22 E
  |/
  o  0: 426bada5c675 A
  
Source overlaps with destination:

  $ rebasewithdag -s 'B+C+D' -d 'map(SRC, "B:C,C:D")' <<'EOS'
  > B C D
  >  \|/
  >   A
  > EOS
  rebasing 2:dc0947a82db8 C "C"
  rebasing 1:112478962961 B "B"
  o  5: 5fe9935d5222 B
  |
  o  4: 12d20731b9e0 C
  |
  o  3: b18e25de2cf5 D
  |
  o  0: 426bada5c675 A
  
Detect cycles early:

  $ rebasewithdag -r 'all()-Z' -d 'map(SRC, "A:B,B:C,C:D,D:B")' <<'EOS'
  > A B C
  >  \|/
  >   | D
  >   |/
  >   Z
  > EOS
  abort: source and destination form a cycle
  [10]

Detect source is ancestor of dest in runtime:

  $ rebasewithdag -r 'C+B' -d 'map(SRC, "C:B,B:D")' -q <<'EOS'
  >   D
  >   |
  > B C
  >  \|
  >   A
  > EOS
  abort: source is ancestor of destination
  [10]

"Already rebased" fast path still works:

  $ rebasewithdag -r 'all()' -d 'SRC^' <<'EOS'
  >   E F
  >  /| |
  > B C D
  >  \|/
  >   A
  > EOS
  already rebased 1:112478962961 B "B"
  already rebased 2:dc0947a82db8 C "C"
  already rebased 3:b18e25de2cf5 D "D"
  already rebased 4:312782b8f06e E "E"
  already rebased 5:ad6717a6a58e F tip "F"
  o  5: ad6717a6a58e F
  |
  o  3: b18e25de2cf5 D
  |
  | o    4: 312782b8f06e E
  | |\
  +---o  2: dc0947a82db8 C
  | |
  | o  1: 112478962961 B
  |/
  o  0: 426bada5c675 A
  
Massively rewrite the DAG:

  $ rebasewithdag -r 'all()' -d 'map(SRC, "A:I,I:null,H:A,B:J,J:C,C:H,D:E,F:G,G:K,K:D,E:B")' <<'EOS'
  > D G K
  > | | |
  > C F J
  > | | |
  > B E I
  >  \| |
  >   A H
  > EOS
  rebasing 4:701514e1408d I "I"
  rebasing 0:426bada5c675 A "A"
  rebasing 1:e7050b6e5048 H "H"
  rebasing 5:26805aba1e60 C "C"
  rebasing 7:cf89f86b485b J "J"
  rebasing 2:112478962961 B "B"
  rebasing 3:7fb047a69f22 E "E"
  rebasing 8:f585351a92f8 D "D"
  rebasing 10:ae41898d7875 K tip "K"
  rebasing 9:711f53bbef0b G "G"
  rebasing 6:64a8289d2492 F "F"
  o  21: 3735afb3713a F
  |
  o  20: 07698142d7a7 G
  |
  o  19: 33aba52e7e72 K
  |
  o  18: 9fdae89dc5a1 D
  |
  o  17: 277dda9a65ee E
  |
  o  16: 9c74fd8657ad B
  |
  o  15: 6527eb0688bb J
  |
  o  14: e94d655b928d C
  |
  o  13: 620d6d349459 H
  |
  o  12: a569a116758f A
  |
  o  11: 2bf1302f5c18 I
  
Resolve instability:

  $ rebasewithdag <<'EOF' -r 'orphan()-obsolete()' -d 'max((successors(max(roots(ALLSRC) & ::SRC)^)-obsolete())::)'
  >      F2
  >      |
  >    J E E2
  >    | |/
  > I2 I | E3
  >   \| |/
  >    H | G
  >    | | |
  >   B2 D F
  >    | |/         # rebase: B -> B2
  >    N C          # amend: E -> E2
  >    | |          # amend: E2 -> E3
  >    M B          # rebase: F -> F2
  >     \|          # amend: I -> I2
  >      A
  > EOF
  6 new orphan changesets
  rebasing 16:5c432343bf59 J tip "J"
  rebasing 3:26805aba1e60 C "C"
  rebasing 6:f585351a92f8 D "D"
  rebasing 10:ffebc37c5d0b E3 "E3"
  rebasing 13:fb184bcfeee8 F2 "F2"
  rebasing 11:dc838ab4c0da G "G"
  o  22: 174f63d574a8 G
  |
  o  21: c9d9fbe76705 F2
  |
  o  20: 0a03c2ede755 E3
  |
  o  19: 228d9d2541b1 D
  |
  o  18: cd856b400c95 C
  |
  o  17: 9148200c858c J
  |
  o  15: eb74780f5094 I2
  |
  o  12: 78309edd643f H
  |
  o  5: 4b4531bd8e1d B2
  |
  o  4: 337c285c272b N
  |
  o  2: 699bc4b6fa22 M
  |
  o  0: 426bada5c675 A