view tests/test-fetch.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.

#require serve

  $ echo "[extensions]" >> $HGRCPATH
  $ echo "fetch=" >> $HGRCPATH

test fetch with default branches only

  $ hg init a
  $ echo a > a/a
  $ hg --cwd a commit -Ama
  adding a
  $ hg clone a b
  updating to branch default
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg clone a c
  updating to branch default
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ echo b > a/b
  $ hg --cwd a commit -Amb
  adding b
  $ hg --cwd a parents -q
  1:d2ae7f538514

should pull one change

  $ hg --cwd b fetch ../a
  pulling from ../a
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 1 changes to 1 files
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg --cwd b parents -q
  1:d2ae7f538514
  $ echo c > c/c
  $ hg --cwd c commit -Amc
  adding c
  $ hg clone c d
  updating to branch default
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg clone c e
  updating to branch default
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved

We cannot use the default commit message if fetching from a local
repo, because the path of the repo will be included in the commit
message, making every commit appear different.
should merge c into a

  $ hg --cwd c fetch -d '0 0' -m 'automated merge' ../a
  pulling from ../a
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 1 changes to 1 files (+1 heads)
  updating to 2:d2ae7f538514
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved
  merging with 1:d36c0562f908
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  new changeset 3:a323a0c43ec4 merges remote changes with local
  $ ls c
  a
  b
  c
  $ hg serve --cwd a -a localhost -p $HGPORT -d --pid-file=hg.pid
  $ cat a/hg.pid >> "$DAEMON_PIDS"

fetch over http, no auth
(this also tests that editor is invoked if '--edit' is specified)

  $ HGEDITOR=cat hg --cwd d fetch --edit http://localhost:$HGPORT/
  pulling from http://localhost:$HGPORT/
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 1 changes to 1 files (+1 heads)
  updating to 2:d2ae7f538514
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved
  merging with 1:d36c0562f908
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  Automated merge with http://localhost:$HGPORT/
  
  
  HG: Enter commit message.  Lines beginning with 'HG:' are removed.
  HG: Leave message empty to abort commit.
  HG: --
  HG: user: test
  HG: branch merge
  HG: branch 'default'
  HG: changed c
  new changeset 3:* merges remote changes with local (glob)
  $ hg --cwd d tip --template '{desc}\n'
  Automated merge with http://localhost:$HGPORT/
  $ hg --cwd d status --rev 'tip^1' --rev tip
  A c
  $ hg --cwd d status --rev 'tip^2' --rev tip
  A b

fetch over http with auth (should be hidden in desc)
(this also tests that editor is not invoked if '--edit' is not
specified, even though commit message is not specified explicitly)

  $ HGEDITOR=cat hg --cwd e fetch http://user:password@localhost:$HGPORT/
  pulling from http://user:***@localhost:$HGPORT/
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 1 changes to 1 files (+1 heads)
  updating to 2:d2ae7f538514
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved
  merging with 1:d36c0562f908
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  new changeset 3:* merges remote changes with local (glob)
  $ hg --cwd e tip --template '{desc}\n'
  Automated merge with http://localhost:$HGPORT/
  $ hg clone a f
  updating to branch default
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg clone a g
  updating to branch default
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ echo f > f/f
  $ hg --cwd f ci -Amf
  adding f
  $ echo g > g/g
  $ hg --cwd g ci -Amg
  adding g
  $ hg clone -q f h
  $ hg clone -q g i

should merge f into g

  $ hg --cwd g fetch -d '0 0' --switch -m 'automated merge' ../f
  pulling from ../f
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 1 changes to 1 files (+1 heads)
  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
  merging with 3:6343ca3eff20
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  new changeset 4:f7faa0b7d3c6 merges remote changes with local
  $ rm i/g

should abort, because i is modified

  $ hg --cwd i fetch ../h
  abort: uncommitted changes
  [255]

test fetch with named branches

  $ hg init nbase
  $ echo base > nbase/a
  $ hg -R nbase ci -Am base
  adding a
  $ hg -R nbase branch a
  marked working directory as branch a
  (branches are permanent and global, did you want a bookmark?)
  $ echo a > nbase/a
  $ hg -R nbase ci -m a
  $ hg -R nbase up -C 0
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg -R nbase branch b
  marked working directory as branch b
  $ echo b > nbase/b
  $ hg -R nbase ci -Am b
  adding b

pull in change on foreign branch

  $ hg clone nbase n1
  updating to branch default
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg clone nbase n2
  updating to branch default
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg -R n1 up -C a
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ echo aa > n1/a
  $ hg -R n1 ci -m a1
  $ hg -R n2 up -C b
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg -R n2 fetch -m 'merge' n1
  pulling from n1
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 1 changes to 1 files

parent should be 2 (no automatic update)

  $ hg -R n2 parents --template '{rev}\n'
  2
  $ rm -fr n1 n2

pull in changes on both foreign and local branches

  $ hg clone nbase n1
  updating to branch default
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg clone nbase n2
  updating to branch default
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg -R n1 up -C a
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ echo aa > n1/a
  $ hg -R n1 ci -m a1
  $ hg -R n1 up -C b
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ echo bb > n1/b
  $ hg -R n1 ci -m b1
  $ hg -R n2 up -C b
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg -R n2 fetch -m 'merge' n1
  pulling from n1
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 2 changesets with 2 changes to 2 files
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved

parent should be 4 (fast forward)

  $ hg -R n2 parents --template '{rev}\n'
  4
  $ rm -fr n1 n2

pull changes on foreign (2 new heads) and local (1 new head) branches
with a local change

  $ hg clone nbase n1
  updating to branch default
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg clone nbase n2
  updating to branch default
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg -R n1 up -C a
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ echo a1 > n1/a
  $ hg -R n1 ci -m a1
  $ hg -R n1 up -C b
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ echo bb > n1/b
  $ hg -R n1 ci -m b1
  $ hg -R n1 up -C 1
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved
  $ echo a2 > n1/a
  $ hg -R n1 ci -m a2
  created new head
  $ hg -R n2 up -C b
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ echo change >> n2/c
  $ hg -R n2 ci -A -m local
  adding c
  $ hg -R n2 fetch -d '0 0' -m 'merge' n1
  pulling from n1
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 3 changesets with 3 changes to 2 files (+2 heads)
  updating to 5:3c4a837a864f
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved
  merging with 3:1267f84a9ea5
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  new changeset 7:2cf2a1261f21 merges remote changes with local

parent should be 7 (new merge changeset)

  $ hg -R n2 parents --template '{rev}\n'
  7
  $ rm -fr n1 n2

pull in changes on foreign (merge of local branch) and local (2 new
heads) with a local change

  $ hg clone nbase n1
  updating to branch default
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg clone nbase n2
  updating to branch default
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg -R n1 up -C a
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg -R n1 merge b
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ hg -R n1 ci -m merge
  $ hg -R n1 up -C 2
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ echo c > n1/a
  $ hg -R n1 ci -m c
  $ hg -R n1 up -C 2
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ echo cc > n1/a
  $ hg -R n1 ci -m cc
  created new head
  $ hg -R n2 up -C b
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ echo change >> n2/b
  $ hg -R n2 ci -A -m local
  $ hg -R n2 fetch -m 'merge' n1
  pulling from n1
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 3 changesets with 2 changes to 1 files (+2 heads)
  not merging with 1 other new branch heads (use "hg heads ." and "hg merge" to merge them)
  [1]

parent should be 3 (fetch did not merge anything)

  $ hg -R n2 parents --template '{rev}\n'
  3
  $ rm -fr n1 n2

pull in change on different branch than dirstate

  $ hg init n1
  $ echo a > n1/a
  $ hg -R n1 ci -Am initial
  adding a
  $ hg clone n1 n2
  updating to branch default
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ echo b > n1/a
  $ hg -R n1 ci -m next
  $ hg -R n2 branch topic
  marked working directory as branch topic
  (branches are permanent and global, did you want a bookmark?)
  $ hg -R n2 fetch -m merge n1
  abort: working directory not at branch tip
  (use 'hg update' to check out branch tip)
  [255]

parent should be 0 (fetch did not update or merge anything)

  $ hg -R n2 parents --template '{rev}\n'
  0
  $ rm -fr n1 n2

test fetch with inactive branches

  $ hg init ib1
  $ echo a > ib1/a
  $ hg --cwd ib1 ci -Am base
  adding a
  $ hg --cwd ib1 branch second
  marked working directory as branch second
  (branches are permanent and global, did you want a bookmark?)
  $ echo b > ib1/b
  $ hg --cwd ib1 ci -Am onsecond
  adding b
  $ hg --cwd ib1 branch -f default
  marked working directory as branch default
  $ echo c > ib1/c
  $ hg --cwd ib1 ci -Am newdefault
  adding c
  created new head
  $ hg clone ib1 ib2
  updating to branch default
  3 files updated, 0 files merged, 0 files removed, 0 files unresolved

fetch should succeed

  $ hg --cwd ib2 fetch ../ib1
  pulling from ../ib1
  searching for changes
  no changes found
  $ rm -fr ib1 ib2

test issue1726

  $ hg init i1726r1
  $ echo a > i1726r1/a
  $ hg --cwd i1726r1 ci -Am base
  adding a
  $ hg clone i1726r1 i1726r2
  updating to branch default
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ echo b > i1726r1/a
  $ hg --cwd i1726r1 ci -m second
  $ echo c > i1726r2/a
  $ hg --cwd i1726r2 ci -m third
  $ HGMERGE=true hg --cwd i1726r2 fetch ../i1726r1
  pulling from ../i1726r1
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 1 changes to 1 files (+1 heads)
  updating to 2:7837755a2789
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  merging with 1:d1f0c6c48ebd
  merging a
  0 files updated, 1 files merged, 0 files removed, 0 files unresolved
  new changeset 3:* merges remote changes with local (glob)
  $ hg --cwd i1726r2 heads default --template '{rev}\n'
  3

test issue2047

  $ hg -q init i2047a
  $ cd i2047a
  $ echo a > a
  $ hg -q ci -Am a
  $ hg -q branch stable
  $ echo b > b
  $ hg -q ci -Am b
  $ cd ..
  $ hg -q clone -r 0 i2047a i2047b
  $ cd i2047b
  $ hg fetch ../i2047a
  pulling from ../i2047a
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 1 changes to 1 files

  $ cd ..