view tests/test-excessive-merge.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

  $ hg init

  $ echo foo > a
  $ echo foo > b
  $ hg add a b

  $ hg ci -m "test"

  $ echo blah > a

  $ hg ci -m "branch a"

  $ hg co 0
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved

  $ echo blah > b

  $ hg ci -m "branch b"
  created new head
  $ HGMERGE=true hg merge 1
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)

  $ hg ci -m "merge b/a -> blah"

  $ hg co 1
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ HGMERGE=true hg merge 2
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ hg ci -m "merge a/b -> blah"
  created new head

  $ hg log
  changeset:   4:2ee31f665a86
  tag:         tip
  parent:      1:96155394af80
  parent:      2:92cc4c306b19
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     merge a/b -> blah
  
  changeset:   3:e16a66a37edd
  parent:      2:92cc4c306b19
  parent:      1:96155394af80
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     merge b/a -> blah
  
  changeset:   2:92cc4c306b19
  parent:      0:5e0375449e74
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     branch b
  
  changeset:   1:96155394af80
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     branch a
  
  changeset:   0:5e0375449e74
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     test
  
  $ hg debugindex --changelog
     rev linkrev nodeid       p1           p2
       0       0 5e0375449e74 000000000000 000000000000
       1       1 96155394af80 5e0375449e74 000000000000
       2       2 92cc4c306b19 5e0375449e74 000000000000
       3       3 e16a66a37edd 92cc4c306b19 96155394af80
       4       4 2ee31f665a86 96155394af80 92cc4c306b19

revision 1
  $ hg manifest --debug 1
  79d7492df40aa0fa093ec4209be78043c181f094 644   a
  2ed2a3912a0b24502043eae84ee4b279c18b90dd 644   b
revision 2
  $ hg manifest --debug 2
  2ed2a3912a0b24502043eae84ee4b279c18b90dd 644   a
  79d7492df40aa0fa093ec4209be78043c181f094 644   b
revision 3
  $ hg manifest --debug 3
  79d7492df40aa0fa093ec4209be78043c181f094 644   a
  79d7492df40aa0fa093ec4209be78043c181f094 644   b
revision 4
  $ hg manifest --debug 4
  79d7492df40aa0fa093ec4209be78043c181f094 644   a
  79d7492df40aa0fa093ec4209be78043c181f094 644   b

  $ hg debugindex a
     rev linkrev nodeid       p1           p2
       0       0 2ed2a3912a0b 000000000000 000000000000
       1       1 79d7492df40a 2ed2a3912a0b 000000000000

  $ hg verify
  checking changesets
  checking manifests
  crosschecking files in changesets and manifests
  checking files
  checked 5 changesets with 4 changes to 2 files