view tests/test-histedit-obsolete.t @ 30155:b7a966ce89ed

changelog: disable delta chains

This patch disables delta chains on changelogs. After this patch, new
entries on changelogs - including existing changelogs - will be stored
as the fulltext of that data (likely compressed). No delta computation
will be performed.

An overview of delta chains and data justifying this change follows.

Revlogs try to store entries as a delta against a previous entry (either
a parent revision in the case of generaldelta or the previous physical
revision when not using generaldelta). Most of the time this is the
correct thing to do: it frequently results in less CPU usage and smaller
storage.

Delta chains are most effective when the base revision being deltad
against is similar to the current data. This tends to occur naturally
for manifests and file data, since only small parts of each tend to
change with each revision. Changelogs, however, are a different story.

Changelog entries represent changesets/commits. And unless commits in a
repository are homogonous (same author, changing same files, similar
commit messages, etc), a delta from one entry to the next tends to be
relatively large compared to the size of the entry. This means that
delta chains tend to be short. How short? Here is the full vs delta
revision breakdown on some real world repos:

Repo             % Full    % Delta   Max Length
hg                45.8       54.2        6
mozilla-central   42.4       57.6        8
mozilla-unified   42.5       57.5       17
pypy              46.1       53.9        6
python-zstandard  46.1       53.9        3

(I threw in python-zstandard as an example of a repo that is homogonous.
It contains a small Python project with changes all from the same
author.)

Contrast this with the manifest revlog for these repos, where 99+% of
revisions are deltas and delta chains run into the thousands.

So delta chains aren't as useful on changelogs. But even a short delta
chain may provide benefits. Let's measure that.

Delta chains may require less CPU to read revisions if the CPU time
spent reading smaller deltas is less than the CPU time used to
decompress larger individual entries. We can measure this via
`hg perfrevlog -c -d 1` to iterate a revlog to resolve each revision's
fulltext. Here are the results of that command on a repo using delta
chains in its changelog and on a repo without delta chains:

hg (forward)
! wall 0.407008 comb 0.410000 user 0.410000 sys 0.000000 (best of 25)
! wall 0.390061 comb 0.390000 user 0.390000 sys 0.000000 (best of 26)

hg (reverse)
! wall 0.515221 comb 0.520000 user 0.520000 sys 0.000000 (best of 19)
! wall 0.400018 comb 0.400000 user 0.390000 sys 0.010000 (best of 25)

mozilla-central (forward)
! wall 4.508296 comb 4.490000 user 4.490000 sys 0.000000 (best of 3)
! wall 4.370222 comb 4.370000 user 4.350000 sys 0.020000 (best of 3)

mozilla-central (reverse)
! wall 5.758995 comb 5.760000 user 5.720000 sys 0.040000 (best of 3)
! wall 4.346503 comb 4.340000 user 4.320000 sys 0.020000 (best of 3)

mozilla-unified (forward)
! wall 4.957088 comb 4.950000 user 4.940000 sys 0.010000 (best of 3)
! wall 4.660528 comb 4.650000 user 4.630000 sys 0.020000 (best of 3)

mozilla-unified (reverse)
! wall 6.119827 comb 6.110000 user 6.090000 sys 0.020000 (best of 3)
! wall 4.675136 comb 4.670000 user 4.670000 sys 0.000000 (best of 3)

pypy (forward)
! wall 1.231122 comb 1.240000 user 1.230000 sys 0.010000 (best of 8)
! wall 1.164896 comb 1.160000 user 1.160000 sys 0.000000 (best of 9)

pypy (reverse)
! wall 1.467049 comb 1.460000 user 1.460000 sys 0.000000 (best of 7)
! wall 1.160200 comb 1.170000 user 1.160000 sys 0.010000 (best of 9)

The data clearly shows that it takes less wall and CPU time to resolve
revisions when there are no delta chains in the changelogs, regardless
of the direction of traversal. Furthermore, not using a delta chain
means that fulltext resolution in reverse is as fast as iterating
forward. So not using delta chains on the changelog is a clear CPU win
for reading operations.

An example of a user-visible operation showing this speed-up is revset
evaluation. Here are results for
`hg perfrevset 'author(gps) or author(mpm)'`:

hg
! wall 1.655506 comb 1.660000 user 1.650000 sys 0.010000 (best of 6)
! wall 1.612723 comb 1.610000 user 1.600000 sys 0.010000 (best of 7)

mozilla-central
! wall 17.629826 comb 17.640000 user 17.600000 sys 0.040000 (best of 3)
! wall 17.311033 comb 17.300000 user 17.260000 sys 0.040000 (best of 3)

What about 00changelog.i size?

Repo                Delta Chains     No Delta Chains
hg                    7,033,250         6,976,771
mozilla-central      82,978,748        81,574,623
mozilla-unified      88,112,349        86,702,162
pypy                 20,740,699        20,659,741

The data shows that removing delta chains from the changelog makes the
changelog smaller.

Delta chains are also used during changegroup generation. This
operation essentially converts a series of revisions to one large
delta chain. And changegroup generation is smart: if the delta in
the revlog matches what the changegroup is emitting, it will reuse
the delta instead of recalculating it. We can measure the impact
removing changelog delta chains has on changegroup generation via
`hg perfchangegroupchangelog`:

hg
! wall 1.589245 comb 1.590000 user 1.590000 sys 0.000000 (best of 7)
! wall 1.788060 comb 1.790000 user 1.790000 sys 0.000000 (best of 6)

mozilla-central
! wall 17.382585 comb 17.380000 user 17.340000 sys 0.040000 (best of 3)
! wall 20.161357 comb 20.160000 user 20.120000 sys 0.040000 (best of 3)

mozilla-unified
! wall 18.722839 comb 18.720000 user 18.680000 sys 0.040000 (best of 3)
! wall 21.168075 comb 21.170000 user 21.130000 sys 0.040000 (best of 3)

pypy
! wall 4.828317 comb 4.830000 user 4.820000 sys 0.010000 (best of 3)
! wall 5.415455 comb 5.420000 user 5.410000 sys 0.010000 (best of 3)

The data shows eliminating delta chains makes the changelog part of
changegroup generation slower. This is expected since we now have to
compute deltas for revisions where we could recycle the delta before.

It is worth putting this regression into context of overall changegroup
times. Here is the rough total CPU time spent in changegroup generation
for various repos while using delta chains on the changelog:

Repo              CPU Time (s)    CPU Time w/ compression
hg                  4.50              7.05
mozilla-central   111.1             222.0
pypy               28.68             75.5

Before compression, removing delta chains from the changegroup adds
~4.4% overhead to hg changegroup generation, 1.3% to mozilla-central,
and 2.0% to pypy. When you factor in zlib compression, these percentages
are roughly divided by 2.

While the increased CPU usage for changegroup generation is unfortunate,
I think it is acceptable because the percentage is small, server
operators (those likely impacted most by this) have other mechanisms
to mitigate CPU consumption (namely reducing zlib compression level and
pre-generated clone bundles), and because there is room to optimize this
in the future. For example, we could use the nullid as the base revision,
effectively encoding the full revision for each entry in the changegroup.
When doing this, `hg perfchangegroupchangelog` nearly halves:

mozilla-unified
! wall 21.168075 comb 21.170000 user 21.130000 sys 0.040000 (best of 3)
! wall 11.196461 comb 11.200000 user 11.190000 sys 0.010000 (best of 3)

This looks very promising as a future optimization opportunity.

It's worth that the changes in test-acl.t to the changegroup part size.
This is because revision 6 in the changegroup had a delta chain of
length 2 before and after this patch the base revision is nullrev.
When the base revision is nullrev, cg2packer.deltaparent() hardcodes
the *previous* revision from the changegroup as the delta parent.
This caused the delta in the changegroup to switch base revisions,
the delta to change, and the size to change accordingly. While the
size increased in this case, I think sizes will remain the same
on average, as the delta base for changelog revisions doesn't matter
too much (as this patch shows). So, I don't consider this a regression.

  $ . "$TESTDIR/histedit-helpers.sh"

Enable obsolete

  $ cat >> $HGRCPATH << EOF
  > [ui]
  > logtemplate= {rev}:{node|short} {desc|firstline}
  > [phases]
  > publish=False
  > [experimental]
  > evolution=createmarkers,allowunstable
  > [extensions]
  > histedit=
  > rebase=
  > EOF

Test that histedit learns about obsolescence not stored in histedit state
  $ hg init boo
  $ cd boo
  $ echo a > a
  $ hg ci -Am a
  adding a
  $ echo a > b
  $ echo a > c
  $ echo a > c
  $ hg ci -Am b
  adding b
  adding c
  $ echo a > d
  $ hg ci -Am c
  adding d
  $ echo "pick `hg log -r 0 -T '{node|short}'`" > plan
  $ echo "pick `hg log -r 2 -T '{node|short}'`" >> plan
  $ echo "edit `hg log -r 1 -T '{node|short}'`" >> plan
  $ hg histedit -r 'all()' --commands plan
  Editing (1b2d564fad96), you may commit or record as needed now.
  (hg histedit --continue to resume)
  [1]
  $ hg st
  A b
  A c
  ? plan
  $ hg commit --amend b
  $ hg histedit --continue
  $ hg log -G
  @  6:46abc7c4d873 b
  |
  o  5:49d44ab2be1b c
  |
  o  0:cb9a9f314b8b a
  
  $ hg debugobsolete
  e72d22b19f8ecf4150ab4f91d0973fd9955d3ddf 49d44ab2be1b67a79127568a67c9c99430633b48 0 (*) {'user': 'test'} (glob)
  3e30a45cf2f719e96ab3922dfe039cfd047956ce 0 {e72d22b19f8ecf4150ab4f91d0973fd9955d3ddf} (*) {'user': 'test'} (glob)
  1b2d564fad96311b45362f17c2aa855150efb35f 46abc7c4d8738e8563e577f7889e1b6db3da4199 0 (*) {'user': 'test'} (glob)
  114f4176969ef342759a8a57e6bccefc4234829b 49d44ab2be1b67a79127568a67c9c99430633b48 0 (*) {'user': 'test'} (glob)

With some node gone missing during the edit.

  $ echo "pick `hg log -r 0 -T '{node|short}'`" > plan
  $ echo "pick `hg log -r 6 -T '{node|short}'`" >> plan
  $ echo "edit `hg log -r 5 -T '{node|short}'`" >> plan
  $ hg histedit -r 'all()' --commands plan
  Editing (49d44ab2be1b), you may commit or record as needed now.
  (hg histedit --continue to resume)
  [1]
  $ hg st
  A b
  A d
  ? plan
  $ hg commit --amend -X . -m XXXXXX
  $ hg commit --amend -X . -m b2
  $ hg --hidden --config extensions.strip= strip 'desc(XXXXXX)' --no-backup
  $ hg histedit --continue
  $ hg log -G
  @  9:273c1f3b8626 c
  |
  o  8:aba7da937030 b2
  |
  o  0:cb9a9f314b8b a
  
  $ hg debugobsolete
  e72d22b19f8ecf4150ab4f91d0973fd9955d3ddf 49d44ab2be1b67a79127568a67c9c99430633b48 0 (*) {'user': 'test'} (glob)
  3e30a45cf2f719e96ab3922dfe039cfd047956ce 0 {e72d22b19f8ecf4150ab4f91d0973fd9955d3ddf} (*) {'user': 'test'} (glob)
  1b2d564fad96311b45362f17c2aa855150efb35f 46abc7c4d8738e8563e577f7889e1b6db3da4199 0 (*) {'user': 'test'} (glob)
  114f4176969ef342759a8a57e6bccefc4234829b 49d44ab2be1b67a79127568a67c9c99430633b48 0 (*) {'user': 'test'} (glob)
  76f72745eac0643d16530e56e2f86e36e40631f1 2ca853e48edbd6453a0674dc0fe28a0974c51b9c 0 (*) {'user': 'test'} (glob)
  2ca853e48edbd6453a0674dc0fe28a0974c51b9c aba7da93703075eec9fb1dbaf143ff2bc1c49d46 0 (*) {'user': 'test'} (glob)
  49d44ab2be1b67a79127568a67c9c99430633b48 273c1f3b86267ed3ec684bb13af1fa4d6ba56e02 0 (*) {'user': 'test'} (glob)
  46abc7c4d8738e8563e577f7889e1b6db3da4199 aba7da93703075eec9fb1dbaf143ff2bc1c49d46 0 (*) {'user': 'test'} (glob)
  $ cd ..

Base setup for the rest of the testing
======================================

  $ hg init base
  $ cd base

  $ for x in a b c d e f ; do
  >     echo $x > $x
  >     hg add $x
  >     hg ci -m $x
  > done

  $ hg log --graph
  @  5:652413bf663e f
  |
  o  4:e860deea161a e
  |
  o  3:055a42cdd887 d
  |
  o  2:177f92b77385 c
  |
  o  1:d2ae7f538514 b
  |
  o  0:cb9a9f314b8b a
  

  $ HGEDITOR=cat hg histedit 1
  pick d2ae7f538514 1 b
  pick 177f92b77385 2 c
  pick 055a42cdd887 3 d
  pick e860deea161a 4 e
  pick 652413bf663e 5 f
  
  # Edit history between d2ae7f538514 and 652413bf663e
  #
  # Commits are listed from least to most recent
  #
  # You can reorder changesets by reordering the lines
  #
  # Commands:
  #
  #  e, edit = use commit, but stop for amending
  #  m, mess = edit commit message without changing commit content
  #  p, pick = use commit
  #  d, drop = remove commit from history
  #  f, fold = use commit, but combine it with the one above
  #  r, roll = like fold, but discard this commit's description
  #
  $ hg histedit 1 --commands - --verbose <<EOF | grep histedit
  > pick 177f92b77385 2 c
  > drop d2ae7f538514 1 b
  > pick 055a42cdd887 3 d
  > fold e860deea161a 4 e
  > pick 652413bf663e 5 f
  > EOF
  [1]
  $ hg log --graph --hidden
  @  10:cacdfd884a93 f
  |
  o  9:59d9f330561f d
  |
  | x  8:b558abc46d09 fold-temp-revision e860deea161a
  | |
  | x  7:96e494a2d553 d
  |/
  o  6:b346ab9a313d c
  |
  | x  5:652413bf663e f
  | |
  | x  4:e860deea161a e
  | |
  | x  3:055a42cdd887 d
  | |
  | x  2:177f92b77385 c
  | |
  | x  1:d2ae7f538514 b
  |/
  o  0:cb9a9f314b8b a
  
  $ hg debugobsolete
  96e494a2d553dd05902ba1cee1d94d4cb7b8faed 0 {b346ab9a313db8537ecf96fca3ca3ca984ef3bd7} (*) {'user': 'test'} (glob)
  b558abc46d09c30f57ac31e85a8a3d64d2e906e4 0 {96e494a2d553dd05902ba1cee1d94d4cb7b8faed} (*) {'user': 'test'} (glob)
  d2ae7f538514cd87c17547b0de4cea71fe1af9fb 0 {cb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b} (*) {'user': 'test'} (glob)
  177f92b773850b59254aa5e923436f921b55483b b346ab9a313db8537ecf96fca3ca3ca984ef3bd7 0 (*) {'user': 'test'} (glob)
  055a42cdd88768532f9cf79daa407fc8d138de9b 59d9f330561fd6c88b1a6b32f0e45034d88db784 0 (*) {'user': 'test'} (glob)
  e860deea161a2f77de56603b340ebbb4536308ae 59d9f330561fd6c88b1a6b32f0e45034d88db784 0 (*) {'user': 'test'} (glob)
  652413bf663ef2a641cab26574e46d5f5a64a55a cacdfd884a9321ec4e1de275ef3949fa953a1f83 0 (*) {'user': 'test'} (glob)


Ensure hidden revision does not prevent histedit
-------------------------------------------------

create an hidden revision

  $ hg histedit 6 --commands - << EOF
  > pick b346ab9a313d 6 c
  > drop 59d9f330561f 7 d
  > pick cacdfd884a93 8 f
  > EOF
  $ hg log --graph
  @  11:c13eb81022ca f
  |
  o  6:b346ab9a313d c
  |
  o  0:cb9a9f314b8b a
  
check hidden revision are ignored (6 have hidden children 7 and 8)

  $ hg histedit 6 --commands - << EOF
  > pick b346ab9a313d 6 c
  > pick c13eb81022ca 8 f
  > EOF



Test that rewriting leaving instability behind is allowed
---------------------------------------------------------------------

  $ hg up '.^'
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
  $ hg log -r 'children(.)'
  11:c13eb81022ca f (no-eol)
  $ hg histedit -r '.' --commands - <<EOF
  > edit b346ab9a313d 6 c
  > EOF
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
  adding c
  Editing (b346ab9a313d), you may commit or record as needed now.
  (hg histedit --continue to resume)
  [1]
  $ echo c >> c
  $ hg histedit --continue

  $ hg log -r 'unstable()'
  11:c13eb81022ca f (no-eol)

stabilise

  $ hg rebase  -r 'unstable()' -d .
  rebasing 11:c13eb81022ca "f"
  $ hg up tip -q

Test dropping of changeset on the top of the stack
-------------------------------------------------------

Nothing is rewritten below, the working directory parent must be change for the
dropped changeset to be hidden.

  $ cd ..
  $ hg clone base droplast
  updating to branch default
  3 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ cd droplast
  $ hg histedit -r '40db8afa467b' --commands - << EOF
  > pick 40db8afa467b 10 c
  > drop b449568bf7fc 11 f
  > EOF
  $ hg log -G
  @  12:40db8afa467b c
  |
  o  0:cb9a9f314b8b a
  

With rewritten ancestors

  $ echo e > e
  $ hg add e
  $ hg commit -m g
  $ echo f > f
  $ hg add f
  $ hg commit -m h
  $ hg histedit -r '40db8afa467b' --commands - << EOF
  > pick 47a8561c0449 12 g
  > pick 40db8afa467b 10 c
  > drop 1b3b05f35ff0 13 h
  > EOF
  $ hg log -G
  @  17:ee6544123ab8 c
  |
  o  16:269e713e9eae g
  |
  o  0:cb9a9f314b8b a
  
  $ cd ../base



Test phases support
===========================================

Check that histedit respect immutability
-------------------------------------------

  $ cat >> $HGRCPATH << EOF
  > [ui]
  > logtemplate= {rev}:{node|short} ({phase}) {desc|firstline}\n
  > EOF

  $ hg ph -pv '.^'
  phase changed for 2 changesets
  $ hg log -G
  @  13:b449568bf7fc (draft) f
  |
  o  12:40db8afa467b (public) c
  |
  o  0:cb9a9f314b8b (public) a
  
  $ hg histedit -r '.~2'
  abort: cannot edit public changeset: cb9a9f314b8b
  (see 'hg help phases' for details)
  [255]


Prepare further testing
-------------------------------------------

  $ for x in g h i j k ; do
  >     echo $x > $x
  >     hg add $x
  >     hg ci -m $x
  > done
  $ hg phase --force --secret .~2
  $ hg log -G
  @  18:ee118ab9fa44 (secret) k
  |
  o  17:3a6c53ee7f3d (secret) j
  |
  o  16:b605fb7503f2 (secret) i
  |
  o  15:7395e1ff83bd (draft) h
  |
  o  14:6b70183d2492 (draft) g
  |
  o  13:b449568bf7fc (draft) f
  |
  o  12:40db8afa467b (public) c
  |
  o  0:cb9a9f314b8b (public) a
  
  $ cd ..

simple phase conservation
-------------------------------------------

Resulting changeset should conserve the phase of the original one whatever the
phases.new-commit option is.

New-commit as draft (default)

  $ cp -r base simple-draft
  $ cd simple-draft
  $ hg histedit -r 'b449568bf7fc' --commands - << EOF
  > edit b449568bf7fc 11 f
  > pick 6b70183d2492 12 g
  > pick 7395e1ff83bd 13 h
  > pick b605fb7503f2 14 i
  > pick 3a6c53ee7f3d 15 j
  > pick ee118ab9fa44 16 k
  > EOF
  0 files updated, 0 files merged, 6 files removed, 0 files unresolved
  adding f
  Editing (b449568bf7fc), you may commit or record as needed now.
  (hg histedit --continue to resume)
  [1]
  $ echo f >> f
  $ hg histedit --continue
  $ hg log -G
  @  24:12e89af74238 (secret) k
  |
  o  23:636a8687b22e (secret) j
  |
  o  22:ccaf0a38653f (secret) i
  |
  o  21:11a89d1c2613 (draft) h
  |
  o  20:c1dec7ca82ea (draft) g
  |
  o  19:087281e68428 (draft) f
  |
  o  12:40db8afa467b (public) c
  |
  o  0:cb9a9f314b8b (public) a
  
  $ cd ..


New-commit as secret (config)

  $ cp -r base simple-secret
  $ cd simple-secret
  $ cat >> .hg/hgrc << EOF
  > [phases]
  > new-commit=secret
  > EOF
  $ hg histedit -r 'b449568bf7fc' --commands - << EOF
  > edit b449568bf7fc 11 f
  > pick 6b70183d2492 12 g
  > pick 7395e1ff83bd 13 h
  > pick b605fb7503f2 14 i
  > pick 3a6c53ee7f3d 15 j
  > pick ee118ab9fa44 16 k
  > EOF
  0 files updated, 0 files merged, 6 files removed, 0 files unresolved
  adding f
  Editing (b449568bf7fc), you may commit or record as needed now.
  (hg histedit --continue to resume)
  [1]
  $ echo f >> f
  $ hg histedit --continue
  $ hg log -G
  @  24:12e89af74238 (secret) k
  |
  o  23:636a8687b22e (secret) j
  |
  o  22:ccaf0a38653f (secret) i
  |
  o  21:11a89d1c2613 (draft) h
  |
  o  20:c1dec7ca82ea (draft) g
  |
  o  19:087281e68428 (draft) f
  |
  o  12:40db8afa467b (public) c
  |
  o  0:cb9a9f314b8b (public) a
  
  $ cd ..


Changeset reordering
-------------------------------------------

If a secret changeset is put before a draft one, all descendant should be secret.
It seems more important to present the secret phase.

  $ cp -r base reorder
  $ cd reorder
  $ hg histedit -r 'b449568bf7fc' --commands - << EOF
  > pick b449568bf7fc 11 f
  > pick 3a6c53ee7f3d 15 j
  > pick 6b70183d2492 12 g
  > pick b605fb7503f2 14 i
  > pick 7395e1ff83bd 13 h
  > pick ee118ab9fa44 16 k
  > EOF
  $ hg log -G
  @  23:558246857888 (secret) k
  |
  o  22:28bd44768535 (secret) h
  |
  o  21:d5395202aeb9 (secret) i
  |
  o  20:21edda8e341b (secret) g
  |
  o  19:5ab64f3a4832 (secret) j
  |
  o  13:b449568bf7fc (draft) f
  |
  o  12:40db8afa467b (public) c
  |
  o  0:cb9a9f314b8b (public) a
  
  $ cd ..

Changeset folding
-------------------------------------------

Folding a secret changeset with a draft one turn the result secret (again,
better safe than sorry). Folding between same phase changeset still works

Note that there is a few reordering in this series for more extensive test

  $ cp -r base folding
  $ cd folding
  $ cat >> .hg/hgrc << EOF
  > [phases]
  > new-commit=secret
  > EOF
  $ hg histedit -r 'b449568bf7fc' --commands - << EOF
  > pick 7395e1ff83bd 13 h
  > fold b449568bf7fc 11 f
  > pick 6b70183d2492 12 g
  > fold 3a6c53ee7f3d 15 j
  > pick b605fb7503f2 14 i
  > fold ee118ab9fa44 16 k
  > EOF
  $ hg log -G
  @  27:f9daec13fb98 (secret) i
  |
  o  24:49807617f46a (secret) g
  |
  o  21:050280826e04 (draft) h
  |
  o  12:40db8afa467b (public) c
  |
  o  0:cb9a9f314b8b (public) a
  
  $ hg co 49807617f46a
  0 files updated, 0 files merged, 2 files removed, 0 files unresolved
  $ echo wat >> wat
  $ hg add wat
  $ hg ci -m 'add wat'
  created new head
  $ hg merge f9daec13fb98
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ hg ci -m 'merge'
  $ echo not wat > wat
  $ hg ci -m 'modify wat'
  $ hg histedit 050280826e04
  abort: cannot edit history that contains merges
  [255]
  $ cd ..