view tests/test-debugbuilddag.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).

plain

  $ hg init
  $ hg debugbuilddag '+2:f +3:p2 @temp <f+4 @default /p2 +2' \
  > --config extensions.progress= --config progress.assume-tty=1 \
  > --config progress.delay=0 --config progress.refresh=0 \
  > --config progress.format=topic,bar,number \
  > --config progress.width=60
  \r (no-eol) (esc)
  building [                                          ]  0/12\r (no-eol) (esc)
  building [                                          ]  0/12\r (no-eol) (esc)
  building [==>                                       ]  1/12\r (no-eol) (esc)
  building [==>                                       ]  1/12\r (no-eol) (esc)
  building [======>                                   ]  2/12\r (no-eol) (esc)
  building [=========>                                ]  3/12\r (no-eol) (esc)
  building [=============>                            ]  4/12\r (no-eol) (esc)
  building [=============>                            ]  4/12\r (no-eol) (esc)
  building [=============>                            ]  4/12\r (no-eol) (esc)
  building [================>                         ]  5/12\r (no-eol) (esc)
  building [====================>                     ]  6/12\r (no-eol) (esc)
  building [=======================>                  ]  7/12\r (no-eol) (esc)
  building [===========================>              ]  8/12\r (no-eol) (esc)
  building [===========================>              ]  8/12\r (no-eol) (esc)
  building [==============================>           ]  9/12\r (no-eol) (esc)
  building [==================================>       ] 10/12\r (no-eol) (esc)
  building [=====================================>    ] 11/12\r (no-eol) (esc)
                                                              \r (no-eol) (esc)

tags
  $ cat .hg/localtags
  66f7d451a68b85ed82ff5fcc254daf50c74144bd f
  bebd167eb94d257ace0e814aeb98e6972ed2970d p2
dag
  $ hg debugdag -t -b
  +2:f
  +3:p2
  @temp*f+3
  @default*/p2+2:tip
tip
  $ hg id
  000000000000
glog
  $ hg log -G --template '{rev}: {desc} [{branches}] @ {date}\n'
  o  11: r11 [] @ 11.00
  |
  o  10: r10 [] @ 10.00
  |
  o    9: r9 [] @ 9.00
  |\
  | o  8: r8 [temp] @ 8.00
  | |
  | o  7: r7 [temp] @ 7.00
  | |
  | o  6: r6 [temp] @ 6.00
  | |
  | o  5: r5 [temp] @ 5.00
  | |
  o |  4: r4 [] @ 4.00
  | |
  o |  3: r3 [] @ 3.00
  | |
  o |  2: r2 [] @ 2.00
  |/
  o  1: r1 [] @ 1.00
  |
  o  0: r0 [] @ 0.00
  

overwritten files, starting on a non-default branch

  $ rm -r .hg
  $ hg init
  $ hg debugbuilddag '@start.@default.:f +3:p2 @temp <f+4 @default /p2 +2' -q -o
tags
  $ cat .hg/localtags
  f778700ebd50fcf282b23a4446bd155da6453eb6 f
  bbccf169769006e2490efd2a02f11c3d38d462bd p2
dag
  $ hg debugdag -t -b
  @start+1
  @default+1:f
  +3:p2
  @temp*f+3
  @default*/p2+2:tip
tip
  $ hg id
  000000000000
glog
  $ hg log -G --template '{rev}: {desc} [{branches}] @ {date}\n'
  o  11: r11 [] @ 11.00
  |
  o  10: r10 [] @ 10.00
  |
  o    9: r9 [] @ 9.00
  |\
  | o  8: r8 [temp] @ 8.00
  | |
  | o  7: r7 [temp] @ 7.00
  | |
  | o  6: r6 [temp] @ 6.00
  | |
  | o  5: r5 [temp] @ 5.00
  | |
  o |  4: r4 [] @ 4.00
  | |
  o |  3: r3 [] @ 3.00
  | |
  o |  2: r2 [] @ 2.00
  |/
  o  1: r1 [] @ 1.00
  |
  o  0: r0 [start] @ 0.00
  
glog of
  $ hg log -G --template '{rev}: {desc} [{branches}]\n' of
  o  11: r11 []
  |
  o  10: r10 []
  |
  o    9: r9 []
  |\
  | o  8: r8 [temp]
  | |
  | o  7: r7 [temp]
  | |
  | o  6: r6 [temp]
  | |
  | o  5: r5 [temp]
  | |
  o |  4: r4 []
  | |
  o |  3: r3 []
  | |
  o |  2: r2 []
  |/
  o  1: r1 []
  |
  o  0: r0 [start]
  
tags
  $ hg tags -v
  tip                               11:9ffe238a67a2
  p2                                 4:bbccf1697690 local
  f                                  1:f778700ebd50 local
cat of
  $ hg cat of --rev tip
  r11


new and mergeable files

  $ rm -r .hg
  $ hg init
  $ hg debugbuilddag '+2:f +3:p2 @temp <f+4 @default /p2 +2' -q -mn
dag
  $ hg debugdag -t -b
  +2:f
  +3:p2
  @temp*f+3
  @default*/p2+2:tip
tip
  $ hg id
  000000000000
glog
  $ hg log -G --template '{rev}: {desc} [{branches}] @ {date}\n'
  o  11: r11 [] @ 11.00
  |
  o  10: r10 [] @ 10.00
  |
  o    9: r9 [] @ 9.00
  |\
  | o  8: r8 [temp] @ 8.00
  | |
  | o  7: r7 [temp] @ 7.00
  | |
  | o  6: r6 [temp] @ 6.00
  | |
  | o  5: r5 [temp] @ 5.00
  | |
  o |  4: r4 [] @ 4.00
  | |
  o |  3: r3 [] @ 3.00
  | |
  o |  2: r2 [] @ 2.00
  |/
  o  1: r1 [] @ 1.00
  |
  o  0: r0 [] @ 0.00
  
glog mf
  $ hg log -G --template '{rev}: {desc} [{branches}]\n' mf
  o  11: r11 []
  |
  o  10: r10 []
  |
  o    9: r9 []
  |\
  | o  8: r8 [temp]
  | |
  | o  7: r7 [temp]
  | |
  | o  6: r6 [temp]
  | |
  | o  5: r5 [temp]
  | |
  o |  4: r4 []
  | |
  o |  3: r3 []
  | |
  o |  2: r2 []
  |/
  o  1: r1 []
  |
  o  0: r0 []
  

man r4
  $ hg manifest -r4
  mf
  nf0
  nf1
  nf2
  nf3
  nf4
cat r4 mf
  $ hg cat -r4 mf
  0 r0
  1
  2 r1
  3
  4 r2
  5
  6 r3
  7
  8 r4
  9
  10
  11
  12
  13
  14
  15
  16
  17
  18
  19
  20
  21
  22
  23
man r8
  $ hg manifest -r8
  mf
  nf0
  nf1
  nf5
  nf6
  nf7
  nf8
cat r8 mf
  $ hg cat -r8 mf
  0 r0
  1
  2 r1
  3
  4
  5
  6
  7
  8
  9
  10 r5
  11
  12 r6
  13
  14 r7
  15
  16 r8
  17
  18
  19
  20
  21
  22
  23
man
  $ hg manifest --rev tip
  mf
  nf0
  nf1
  nf10
  nf11
  nf2
  nf3
  nf4
  nf5
  nf6
  nf7
  nf8
  nf9
cat mf
  $ hg cat mf --rev tip
  0 r0
  1
  2 r1
  3
  4 r2
  5
  6 r3
  7
  8 r4
  9
  10 r5
  11
  12 r6
  13
  14 r7
  15
  16 r8
  17
  18 r9
  19
  20 r10
  21
  22 r11
  23