view tests/test-rebase-detach.t @ 33207:895ecec31c70

revlog: add an experimental option to mitigated delta issues (issue5480)

The general delta heuristic to select a delta do not scale with the number of
branch. The delta base is frequently too far away to be able to reuse a chain
according to the "distance" criteria. This leads to insertion of larger delta (or
even full text) that themselves push the bases for the next delta further away
leading to more large deltas and full texts. This full text and frequent
recomputation throw Mercurial performance in disarray.

For example of a slightly large repository

  280 000 files (2 150 000 versions)
  430 000 changesets (10 000 topological heads)

Number below compares repository with and without the distance criteria:

manifest size:
    with:    21.4 GB
    without:  0.3 GB

store size:
    with:    28.7 GB
    without   7.4 GB

bundle last 15 00 revisions:
    with:    800 seconds
             971 MB
    without:  50 seconds
              73 MB

unbundle time (of the last 15K revisions):
    with:    1150 seconds (~19 minutes)
    without:   35 seconds

Similar issues has been observed in other repositories.


Adding a new option or "feature" on stable is uncommon. However, given that this
issues is making Mercurial practically unusable, I'm exceptionally targeting
this patch for stable.

What is actually needed is a full rework of the delta building and reading
logic. However, that will be a longer process and churn not suitable for stable.

In the meantime, we introduces a quick and dirty mitigation of this in the
'experimental' config space. The new option introduces a way to set the maximum
amount of memory usable to store a diff in memory. This extend the ability for
Mercurial to create chains without removing all safe guard regarding memory
access. The option should be phased out when core has a more proper solution
available.

Setting the limit to '0' remove all limits, setting it to '-1' use the default
limit (textsize x 4).

  $ cat >> $HGRCPATH <<EOF
  > [extensions]
  > rebase=
  > 
  > [phases]
  > publish=False
  > 
  > [alias]
  > tglog = log -G --template "{rev}: '{desc}' {branches}\n"
  > EOF


  $ hg init a
  $ cd a
  $ hg unbundle "$TESTDIR/bundles/rebase.hg"
  adding changesets
  adding manifests
  adding file changes
  added 8 changesets with 7 changes to 7 files (+2 heads)
  (run 'hg heads' to see heads, 'hg merge' to merge)
  $ hg up tip
  3 files updated, 0 files merged, 0 files removed, 0 files unresolved

  $ cd ..


Rebasing D onto H detaching from C:

  $ hg clone -q -u . a a1
  $ cd a1

  $ hg tglog
  @  7: 'H'
  |
  | o  6: 'G'
  |/|
  o |  5: 'F'
  | |
  | o  4: 'E'
  |/
  | o  3: 'D'
  | |
  | o  2: 'C'
  | |
  | o  1: 'B'
  |/
  o  0: 'A'
  
  $ hg phase --force --secret 3
  $ hg rebase -s 3 -d 7
  rebasing 3:32af7686d403 "D"
  saved backup bundle to $TESTTMP/a1/.hg/strip-backup/32af7686d403-6f7dface-backup.hg (glob)

  $ hg log -G --template "{rev}:{phase} '{desc}' {branches}\n"
  o  7:secret 'D'
  |
  @  6:draft 'H'
  |
  | o  5:draft 'G'
  |/|
  o |  4:draft 'F'
  | |
  | o  3:draft 'E'
  |/
  | o  2:draft 'C'
  | |
  | o  1:draft 'B'
  |/
  o  0:draft 'A'
  
  $ hg manifest --rev tip
  A
  D
  F
  H

  $ cd ..


Rebasing C onto H detaching from B:

  $ hg clone -q -u . a a2
  $ cd a2

  $ hg tglog
  @  7: 'H'
  |
  | o  6: 'G'
  |/|
  o |  5: 'F'
  | |
  | o  4: 'E'
  |/
  | o  3: 'D'
  | |
  | o  2: 'C'
  | |
  | o  1: 'B'
  |/
  o  0: 'A'
  
  $ hg rebase -s 2 -d 7
  rebasing 2:5fddd98957c8 "C"
  rebasing 3:32af7686d403 "D"
  saved backup bundle to $TESTTMP/a2/.hg/strip-backup/5fddd98957c8-f9244fa1-backup.hg (glob)

  $ hg tglog
  o  7: 'D'
  |
  o  6: 'C'
  |
  @  5: 'H'
  |
  | o  4: 'G'
  |/|
  o |  3: 'F'
  | |
  | o  2: 'E'
  |/
  | o  1: 'B'
  |/
  o  0: 'A'
  
  $ hg manifest --rev tip
  A
  C
  D
  F
  H

  $ cd ..


Rebasing B onto H using detach (same as not using it):

  $ hg clone -q -u . a a3
  $ cd a3

  $ hg tglog
  @  7: 'H'
  |
  | o  6: 'G'
  |/|
  o |  5: 'F'
  | |
  | o  4: 'E'
  |/
  | o  3: 'D'
  | |
  | o  2: 'C'
  | |
  | o  1: 'B'
  |/
  o  0: 'A'
  
  $ hg rebase -s 1 -d 7
  rebasing 1:42ccdea3bb16 "B"
  rebasing 2:5fddd98957c8 "C"
  rebasing 3:32af7686d403 "D"
  saved backup bundle to $TESTTMP/a3/.hg/strip-backup/42ccdea3bb16-3cb021d3-backup.hg (glob)

  $ hg tglog
  o  7: 'D'
  |
  o  6: 'C'
  |
  o  5: 'B'
  |
  @  4: 'H'
  |
  | o  3: 'G'
  |/|
  o |  2: 'F'
  | |
  | o  1: 'E'
  |/
  o  0: 'A'
  
  $ hg manifest --rev tip
  A
  B
  C
  D
  F
  H

  $ cd ..


Rebasing C onto H detaching from B and collapsing:

  $ hg clone -q -u . a a4
  $ cd a4
  $ hg phase --force --secret 3

  $ hg tglog
  @  7: 'H'
  |
  | o  6: 'G'
  |/|
  o |  5: 'F'
  | |
  | o  4: 'E'
  |/
  | o  3: 'D'
  | |
  | o  2: 'C'
  | |
  | o  1: 'B'
  |/
  o  0: 'A'
  
  $ hg rebase --collapse -s 2 -d 7
  rebasing 2:5fddd98957c8 "C"
  rebasing 3:32af7686d403 "D"
  saved backup bundle to $TESTTMP/a4/.hg/strip-backup/5fddd98957c8-f9244fa1-backup.hg (glob)

  $ hg  log -G --template "{rev}:{phase} '{desc}' {branches}\n"
  o  6:secret 'Collapsed revision
  |  * C
  |  * D'
  @  5:draft 'H'
  |
  | o  4:draft 'G'
  |/|
  o |  3:draft 'F'
  | |
  | o  2:draft 'E'
  |/
  | o  1:draft 'B'
  |/
  o  0:draft 'A'
  
  $ hg manifest --rev tip
  A
  C
  D
  F
  H

  $ cd ..

Rebasing across null as ancestor
  $ hg clone -q -U a a5

  $ cd a5

  $ echo x > x

  $ hg add x

  $ hg ci -m "extra branch"
  created new head

  $ hg tglog
  @  8: 'extra branch'
  
  o  7: 'H'
  |
  | o  6: 'G'
  |/|
  o |  5: 'F'
  | |
  | o  4: 'E'
  |/
  | o  3: 'D'
  | |
  | o  2: 'C'
  | |
  | o  1: 'B'
  |/
  o  0: 'A'
  
  $ hg rebase -s 1 -d tip
  rebasing 1:42ccdea3bb16 "B"
  rebasing 2:5fddd98957c8 "C"
  rebasing 3:32af7686d403 "D"
  saved backup bundle to $TESTTMP/a5/.hg/strip-backup/42ccdea3bb16-3cb021d3-backup.hg (glob)

  $ hg tglog
  o  8: 'D'
  |
  o  7: 'C'
  |
  o  6: 'B'
  |
  @  5: 'extra branch'
  
  o  4: 'H'
  |
  | o  3: 'G'
  |/|
  o |  2: 'F'
  | |
  | o  1: 'E'
  |/
  o  0: 'A'
  

  $ hg rebase -d 5 -s 7
  rebasing 7:13547172c9c0 "C"
  rebasing 8:4e27a76c371a "D" (tip)
  saved backup bundle to $TESTTMP/a5/.hg/strip-backup/13547172c9c0-35685ded-backup.hg (glob)
  $ hg tglog
  o  8: 'D'
  |
  o  7: 'C'
  |
  | o  6: 'B'
  |/
  @  5: 'extra branch'
  
  o  4: 'H'
  |
  | o  3: 'G'
  |/|
  o |  2: 'F'
  | |
  | o  1: 'E'
  |/
  o  0: 'A'
  
  $ cd ..

Verify that target is not selected as external rev (issue3085)

  $ hg clone -q -U a a6
  $ cd a6
  $ hg up -q 6

  $ echo "I" >> E
  $ hg ci -m "I"
  $ hg merge 7
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ hg ci -m "Merge"
  $ echo "J" >> F
  $ hg ci -m "J"

  $ hg rebase -s 8 -d 7 --collapse --config ui.merge=internal:other
  rebasing 8:9790e768172d "I"
  rebasing 9:5d7b11f5fb97 "Merge"
  rebasing 10:9427d4d5af81 "J" (tip)
  saved backup bundle to $TESTTMP/a6/.hg/strip-backup/9790e768172d-c2111e9d-backup.hg (glob)

  $ hg tglog
  @  8: 'Collapsed revision
  |  * I
  |  * Merge
  |  * J'
  o  7: 'H'
  |
  | o  6: 'G'
  |/|
  o |  5: 'F'
  | |
  | o  4: 'E'
  |/
  | o  3: 'D'
  | |
  | o  2: 'C'
  | |
  | o  1: 'B'
  |/
  o  0: 'A'
  

  $ hg log --rev tip
  changeset:   8:9472f4b1d736
  tag:         tip
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     Collapsed revision
  

  $ cd ..

Ensure --continue restores a correct state (issue3046) and phase:
  $ hg clone -q a a7
  $ cd a7
  $ hg up -q 3
  $ echo 'H2' > H
  $ hg ci -A -m 'H2'
  adding H
  $ hg phase --force --secret 8
  $ hg rebase -s 8 -d 7 --config ui.merge=internal:fail
  rebasing 8:6215fafa5447 "H2" (tip)
  merging H
  warning: conflicts while merging H! (edit, then use 'hg resolve --mark')
  unresolved conflicts (see hg resolve, then hg rebase --continue)
  [1]
  $ hg resolve --all -t internal:local
  (no more unresolved files)
  continue: hg rebase --continue
  $ hg rebase -c
  rebasing 8:6215fafa5447 "H2" (tip)
  note: rebase of 8:6215fafa5447 created no changes to commit
  saved backup bundle to $TESTTMP/a7/.hg/strip-backup/6215fafa5447-5804ebd5-backup.hg (glob)
  $ hg  log -G --template "{rev}:{phase} '{desc}' {branches}\n"
  @  7:draft 'H'
  |
  | o  6:draft 'G'
  |/|
  o |  5:draft 'F'
  | |
  | o  4:draft 'E'
  |/
  | o  3:draft 'D'
  | |
  | o  2:draft 'C'
  | |
  | o  1:draft 'B'
  |/
  o  0:draft 'A'
  

  $ cd ..