view tests/test-rebase-issue-noparam-single-rev.t @ 47120:7109a38830c9

dirstate-tree: Fold "tracked descendants" counter update in main walk

For the purpose of implementing `has_tracked_dir` (which means "has tracked
descendants) without an expensive sub-tree traversal, we maintaing a counter
of tracked descendants on each "directory" node of the tree-shaped dirstate.

Before this changeset, mutating or inserting a node at a given path would
involve:

* Walking the tree from root through ancestors to find the node or the spot
  where to insert it
* Looking at the previous node if any to decide what counter update is needed
* Performing any node mutation
* Walking the tree *again* to update counters in ancestor nodes

When profiling `hg status` on a large repo, this second walk takes times
while loading a the dirstate from disk.

It turns out we have enough information to decide before he first tree walk
what counter update is needed. This changeset merges the two walks, gaining
~10% of the total time for `hg update` (in the same hyperfine benchmark as
the previous changeset).

---

Profiling was done by compiling with this `.cargo/config`:

    [profile.release]
    debug = true

then running with:

    py-spy record -r 500 -n -o /tmp/hg.json --format speedscope -- \
    ./hg status -R $REPO --config experimental.dirstate-tree.in-memory=1

then visualizing the recorded JSON file in https://www.speedscope.app/

Differential Revision: https://phab.mercurial-scm.org/D10554

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


  $ hg init a
  $ cd a

  $ echo c1 > c1
  $ hg ci -Am c1
  adding c1

  $ echo c2 > c2
  $ hg ci -Am c2
  adding c2

  $ echo l1 > l1
  $ hg ci -Am l1
  adding l1

  $ hg up -q -C 1

  $ echo r1 > r1
  $ hg ci -Am r1
  adding r1
  created new head

  $ echo r2 > r2
  $ hg ci -Am r2
  adding r2

  $ hg tglog
  @  4: 225af64d03e6 'r2'
  |
  o  3: 8d0a8c99b309 'r1'
  |
  | o  2: 87c180a611f2 'l1'
  |/
  o  1: 56daeba07f4b 'c2'
  |
  o  0: e8faad3d03ff 'c1'
  
Rebase with no arguments - single revision in source branch:

  $ hg up -q -C 2

  $ hg rebase
  rebasing 2:87c180a611f2 "l1"
  saved backup bundle to $TESTTMP/a/.hg/strip-backup/87c180a611f2-a5be192d-rebase.hg

  $ hg tglog
  @  4: b1152cc99655 'l1'
  |
  o  3: 225af64d03e6 'r2'
  |
  o  2: 8d0a8c99b309 'r1'
  |
  o  1: 56daeba07f4b 'c2'
  |
  o  0: e8faad3d03ff 'c1'
  
  $ cd ..


  $ hg init b
  $ cd b

  $ echo c1 > c1
  $ hg ci -Am c1
  adding c1

  $ echo c2 > c2
  $ hg ci -Am c2
  adding c2

  $ echo l1 > l1
  $ hg ci -Am l1
  adding l1

  $ echo l2 > l2
  $ hg ci -Am l2
  adding l2

  $ hg up -q -C 1

  $ echo r1 > r1
  $ hg ci -Am r1
  adding r1
  created new head

  $ hg tglog
  @  4: 8d0a8c99b309 'r1'
  |
  | o  3: 1ac923b736ef 'l2'
  | |
  | o  2: 87c180a611f2 'l1'
  |/
  o  1: 56daeba07f4b 'c2'
  |
  o  0: e8faad3d03ff 'c1'
  
Rebase with no arguments - single revision in target branch:

  $ hg up -q -C 3

  $ hg rebase
  rebasing 2:87c180a611f2 "l1"
  rebasing 3:1ac923b736ef "l2"
  saved backup bundle to $TESTTMP/b/.hg/strip-backup/87c180a611f2-b980535c-rebase.hg

  $ hg tglog
  @  4: 023181307ed0 'l2'
  |
  o  3: 913ab52b43b4 'l1'
  |
  o  2: 8d0a8c99b309 'r1'
  |
  o  1: 56daeba07f4b 'c2'
  |
  o  0: e8faad3d03ff 'c1'
  

  $ cd ..