view tests/test-exchange-obsmarkers-case-D3.t @ 38732:be4984261611

merge: mark file gets as not thread safe (issue5933)

In default installs, this has the effect of disabling the thread-based
worker on Windows when manifesting files in the working directory. My
measurements have shown that with revlog-based repositories, Mercurial
spends a lot of CPU time in revlog code resolving file data. This ends
up incurring a lot of context switching across threads and slows down
`hg update` operations when going from an empty working directory to
the tip of the repo.

On mozilla-unified (246,351 files) on an i7-6700K (4+4 CPUs):

before: 487s wall
after:  360s wall (equivalent to worker.enabled=false)
cpus=2: 379s wall

Even with only 2 threads, the thread pool is still slower.

The introduction of the thread-based worker (02b36e860e0b) states that
it resulted in a "~50%" speedup for `hg sparse --enable-profile` and
`hg sparse --disable-profile`. This disagrees with my measurement
above. I theorize a few reasons for this:

1) Removal of files from the working directory is I/O - not CPU - bound
   and should benefit from a thread pool (unless I/O is insanely fast
   and the GIL release is near instantaneous). So tests like `hg sparse
   --enable-profile` may exercise deletion throughput and aren't good
   benchmarks for worker tasks that are CPU heavy.
2) The patch was authored by someone at Facebook. The results were
   likely measured against a repository using remotefilelog. And I
   believe that revision retrieval during working directory updates with
   remotefilelog will often use a remote store, thus being I/O and not
   CPU bound. This probably resulted in an overstated performance gain.

Since there appears to be a need to enable the thread-based worker with
some stores, I've made the flagging of file gets as thread safe
configurable. I've made it experimental because I don't want to formalize
a boolean flag for this option and because this attribute is best
captured against the store implementation. But we don't have a proper
store API for this yet. I'd rather cross this bridge later.

It is possible there are revlog-based repositories that do benefit from
a thread-based worker. I didn't do very comprehensive testing. If there
are, we may want to devise a more proper algorithm for whether to use
the thread-based worker, including possibly config options to limit the
number of threads to use. But until I see evidence that justifies
complexity, simplicity wins.

Differential Revision: https://phab.mercurial-scm.org/D3963

============================================
Testing obsolescence markers push: Cases D.3
============================================

Mercurial pushes obsolescences markers relevant to the "pushed-set", the set of
all changesets that requested to be "in sync" after the push (even if they are
already on both side).

This test belongs to a series of tests checking such set is properly computed
and applied. This does not tests "obsmarkers" discovery capabilities.

Category D: Partial Information Case
TestCase 3: missing prune target (prune not in "pushed set")

D.3 missing prune target (prune not in "pushed set")
====================================================

.. {{{
..  A ø⇠✕ A'
..     | |
..     | ○ B
..     |/
..     ● O
.. }}}
..
.. Marker exist from:
..
..  * `A ø⇠o A'`
..  * A' (prune)
..
.. Command runs:
..
..  * hg push
..
.. Expected exclude:
..
..  * `A ø⇠o A'`
..  * A' (prune)

Setup
-----

  $ . $TESTDIR/testlib/exchange-obsmarker-util.sh

initial

  $ setuprepos D.3
  creating test repo for test case D.3
  - pulldest
  - main
  - pushdest
  cd into `main` and proceed with env setup
  $ cd main
  $ mkcommit A0
  $ hg up -q 0
  $ mkcommit B
  created new head
  $ mkcommit A1
  $ hg debugobsolete `getid 'desc(A0)'` `getid 'desc(A1)'`
  obsoleted 1 changesets
  $ hg prune -d '0 0' .
  obsoleted 1 changesets
  $ hg strip --hidden -q 'desc(A1)'
  $ hg log -G --hidden
  @  35b183996678 (draft): B
  |
  | x  28b51eb45704 (draft): A0
  |/
  o  a9bdc8b26820 (public): O
  
  $ inspect_obsmarkers
  obsstore content
  ================
  28b51eb45704506b5c603decd6bf7ac5e0f6a52f 6aa67a7b4baa6fb41b06aed38d5b1201436546e2 0 (Thu Jan 01 00:00:00 1970 +0000) {'user': 'test'}
  6aa67a7b4baa6fb41b06aed38d5b1201436546e2 0 {35b1839966785d5703a01607229eea932db42f87} (Thu Jan 01 00:00:00 1970 +0000) {'user': 'test'}
  $ cd ..
  $ cd ..

Actual Test
-----------

  $ dotest D.3 O
  ## Running testcase D.3
  # testing echange of "O" (a9bdc8b26820)
  ## initial state
  # obstore: main
  28b51eb45704506b5c603decd6bf7ac5e0f6a52f 6aa67a7b4baa6fb41b06aed38d5b1201436546e2 0 (Thu Jan 01 00:00:00 1970 +0000) {'user': 'test'}
  6aa67a7b4baa6fb41b06aed38d5b1201436546e2 0 {35b1839966785d5703a01607229eea932db42f87} (Thu Jan 01 00:00:00 1970 +0000) {'user': 'test'}
  # obstore: pushdest
  # obstore: pulldest
  ## pushing "O" from main to pushdest
  pushing to pushdest
  searching for changes
  no changes found
  ## post push state
  # obstore: main
  28b51eb45704506b5c603decd6bf7ac5e0f6a52f 6aa67a7b4baa6fb41b06aed38d5b1201436546e2 0 (Thu Jan 01 00:00:00 1970 +0000) {'user': 'test'}
  6aa67a7b4baa6fb41b06aed38d5b1201436546e2 0 {35b1839966785d5703a01607229eea932db42f87} (Thu Jan 01 00:00:00 1970 +0000) {'user': 'test'}
  # obstore: pushdest
  # obstore: pulldest
  ## pulling "a9bdc8b26820" from main into pulldest
  pulling from main
  no changes found
  ## post pull state
  # obstore: main
  28b51eb45704506b5c603decd6bf7ac5e0f6a52f 6aa67a7b4baa6fb41b06aed38d5b1201436546e2 0 (Thu Jan 01 00:00:00 1970 +0000) {'user': 'test'}
  6aa67a7b4baa6fb41b06aed38d5b1201436546e2 0 {35b1839966785d5703a01607229eea932db42f87} (Thu Jan 01 00:00:00 1970 +0000) {'user': 'test'}
  # obstore: pushdest
  # obstore: pulldest