view tests/test-bookmarks-strip.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

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

  $ hg init

  $ echo qqq>qqq.txt

rollback dry run without rollback information

  $ hg rollback
  no rollback information available
  [1]

add file

  $ hg add
  adding qqq.txt

commit first revision

  $ hg ci -m 1

set bookmark

  $ hg book test

  $ echo www>>qqq.txt

commit second revision

  $ hg ci -m 2

set bookmark

  $ hg book test2

update to -2 (deactivates the active bookmark)

  $ hg update -r -2
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (leaving bookmark test2)

  $ echo eee>>qqq.txt

commit new head

  $ hg ci -m 3
  created new head

bookmarks updated?

  $ hg book
     test                      1:25e1ee7a0081
     test2                     1:25e1ee7a0081

strip to revision 1

  $ hg strip 1
  saved backup bundle to $TESTTMP/.hg/strip-backup/*-backup.hg (glob)

list bookmarks

  $ hg book
     test                      0:5c9ad3787638
     test2                     0:5c9ad3787638