view tests/test-merge7.t @ 42743:8c9a6adec67a

rust-discovery: using the children cache in add_missing

The DAG range computation often needs to get back to very old
revisions, and turns out to be disproportionately long, given
that the end goal is to remove the descendents of the given
missing revisons from the undecided set.

The fast iteration capabilities available in the Rust case make
it possible to avoid the DAG range entirely, at the cost of
precomputing the children cache, and to simply iterate on
children of the given missing revisions.

This is a case where staying on the same side of the interface
between the two languages has clear benefits.

On discoveries with initial undecided sets
small enough to bypass sampling entirely, the total cost of
computing the children cache and the subsequent iteration
becomes better than the Python + C counterpart, which relies on
reachableroots2.

For example, on a repo with more than one million revisions with
an initial undecided set of 11 elements, we get these figures:

Rust version with simple iteration
  addcommons: 57.287us
  first undecided computation: 184.278334ms
  first children cache computation: 131.056us
  addmissings iteration: 42.766us
  first addinfo total: 185.24 ms

Python + C version
  first addcommons: 0.29 ms
  addcommons 0.21 ms
  first undecided computation 191.35 ms
  addmissings 45.75 ms
  first addinfo total: 237.77 ms

On discoveries with large undecided sets, the initial price paid
makes the first addinfo slower than the Python + C version,
but that's more than compensated by the gain in sampling and
subsequent iterations.
Here's an extreme example with an undecided set of a million revisions:

Rust version:
  first undecided computation: 293.842629ms
  first children cache computation: 407.911297ms
  addmissings iteration: 34.312869ms
  first addinfo total: 776.02 ms
  taking initial sample
  query 2: sampling time: 1318.38 ms
  query 2; still undecided: 1005013, sample size is: 200
  addmissings: 143.062us

Python + C version:
  first undecided computation 298.13 ms
  addmissings 80.13 ms
  first addinfo total: 399.62 ms
  taking initial sample
  query 2: sampling time: 3957.23 ms
  query 2; still undecided: 1005013, sample size is: 200
  addmissings 52.88 ms

Differential Revision: https://phab.mercurial-scm.org/D6428

initial
  $ hg init test-a
  $ cd test-a
  $ cat >test.txt <<"EOF"
  > 1
  > 2
  > 3
  > EOF
  $ hg add test.txt
  $ hg commit -m "Initial"

clone
  $ cd ..
  $ hg clone test-a test-b
  updating to branch default
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved

change test-a
  $ cd test-a
  $ cat >test.txt <<"EOF"
  > one
  > two
  > three
  > EOF
  $ hg commit -m "Numbers as words"

change test-b
  $ cd ../test-b
  $ cat >test.txt <<"EOF"
  > 1
  > 2.5
  > 3
  > EOF
  $ hg commit -m "2 -> 2.5"

now pull and merge from test-a
  $ hg pull ../test-a
  pulling from ../test-a
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 1 changes to 1 files (+1 heads)
  new changesets 96b70246a118
  (run 'hg heads' to see heads, 'hg merge' to merge)
  $ hg merge
  merging test.txt
  warning: conflicts while merging test.txt! (edit, then use 'hg resolve --mark')
  0 files updated, 0 files merged, 0 files removed, 1 files unresolved
  use 'hg resolve' to retry unresolved file merges or 'hg merge --abort' to abandon
  [1]
resolve conflict
  $ cat >test.txt <<"EOF"
  > one
  > two-point-five
  > three
  > EOF
  $ rm -f *.orig
  $ hg resolve -m test.txt
  (no more unresolved files)
  $ hg commit -m "Merge 1"

change test-a again
  $ cd ../test-a
  $ cat >test.txt <<"EOF"
  > one
  > two-point-one
  > three
  > EOF
  $ hg commit -m "two -> two-point-one"

pull and merge from test-a again
  $ cd ../test-b
  $ hg pull ../test-a
  pulling from ../test-a
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 1 changes to 1 files (+1 heads)
  new changesets 40d11a4173a8
  (run 'hg heads' to see heads, 'hg merge' to merge)
  $ hg merge --debug
  resolving manifests
   branchmerge: True, force: False, partial: False
   ancestor: 96b70246a118, local: 50c3a7e29886+, remote: 40d11a4173a8
   preserving test.txt for resolve of test.txt
  starting 4 threads for background file closing (?)
   test.txt: versions differ -> m (premerge)
  picked tool ':merge' for test.txt (binary False symlink False changedelete False)
  merging test.txt
  my test.txt@50c3a7e29886+ other test.txt@40d11a4173a8 ancestor test.txt@96b70246a118
   test.txt: versions differ -> m (merge)
  picked tool ':merge' for test.txt (binary False symlink False changedelete False)
  my test.txt@50c3a7e29886+ other test.txt@40d11a4173a8 ancestor test.txt@96b70246a118
  warning: conflicts while merging test.txt! (edit, then use 'hg resolve --mark')
  0 files updated, 0 files merged, 0 files removed, 1 files unresolved
  use 'hg resolve' to retry unresolved file merges or 'hg merge --abort' to abandon
  [1]

  $ cat test.txt
  one
  <<<<<<< working copy: 50c3a7e29886 - test: Merge 1
  two-point-five
  =======
  two-point-one
  >>>>>>> merge rev:    40d11a4173a8 - test: two -> two-point-one
  three

  $ hg debugindex test.txt
     rev linkrev nodeid       p1           p2
       0       0 01365c4cca56 000000000000 000000000000
       1       1 7b013192566a 01365c4cca56 000000000000
       2       2 8fe46a3eb557 01365c4cca56 000000000000
       3       3 fc3148072371 7b013192566a 8fe46a3eb557
       4       4 d40249267ae3 8fe46a3eb557 000000000000

  $ hg log
  changeset:   4:40d11a4173a8
  tag:         tip
  parent:      2:96b70246a118
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     two -> two-point-one
  
  changeset:   3:50c3a7e29886
  parent:      1:d1e159716d41
  parent:      2:96b70246a118
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     Merge 1
  
  changeset:   2:96b70246a118
  parent:      0:b1832b9d912a
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     Numbers as words
  
  changeset:   1:d1e159716d41
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     2 -> 2.5
  
  changeset:   0:b1832b9d912a
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     Initial
  

  $ cd ..