view tests/test-bookmarks-push-race.t @ 51681:522b4d729e89

mmap: populate the mapping by default

Without pre-population, accessing all data through a mmap can result in many
pagefault, reducing performance significantly. If the mmap is prepopulated, the
performance can no longer get slower than a full read.
(See benchmark number below)

In some cases were very few data is read, prepopulating can be overkill and
slower than populating on access (through page fault). So that behavior can be
controlled when the caller can pre-determine the best behavior.
(See benchmark number below)

In addition, testing with populating in a secondary thread yield great result
combining the best of each approach. This might be implemented in later
changesets.

In all cases, using mmap has a great effect on memory usage when many processes
run in parallel on the same machine.

### Benchmarks

# What did I run

A couple of month back I ran a large benchmark campaign to assess the impact of
various approach for using mmap with the revlog (and other files), it
highlighted a few benchmarks that capture the impact of the changes well. So to
validate this change I checked the following:

- log command displaying various revisions
  (read the changelog index)
- log command displaying the patch of listed revisions
  (read the changelog index, the manifest index and a few files indexes)
- unbundling a few revisions
  (read and write changelog, manifest and few files indexes, and walk the graph
  to update some cache)
- pushing a few revisions
  (read and write changelog, manifest and few files indexes, walk the graph to
  update some cache, performs various accesses locally and remotely during
  discovery)

Benchmarks were run using the default module policy (c+py) and the rust one. No
significant difference were found between the two implementation, so we will
present result using the default policy (unless otherwise specified).

I ran them on a few repositories :

- mercurial: a "public changeset only" copy of mercurial from 2018-08-01 using
  zstd compression and sparse-revlog

- pypy: a copy of pypy from 2018-08-01 using zstd compression and sparse-revlog

- netbeans: a copy of netbeans from 2018-08-01 using zstd compression and
  sparse-revlog

- mozilla-try: a copy of mozilla-try from 2019-02-18 using zstd compression and
  sparse-revlog

- mozilla-try persistent-nodemap: Same as the above but with a persistent
  nodemap. Used for the log --patch benchmark only

# Results

For the smaller repositories (mercurial, pypy), the impact of mmap is almost
imperceptible, other cost dominating the operation. The impact of prepopulating
is undiscernible in the benchmark we ran.

For larger repositories the benchmark support explanation given above:

On netbeans, the log can be about 1% faster without repopulation (for a
difference < 100ms) but unbundle becomes a bit slower, even when small.

### data-env-vars.name                             = netbeans-2018-08-01-zstd-sparse-revlog
  # benchmark.name                                 = hg.command.unbundle
  # benchmark.variants.issue6528                   = disabled
  # benchmark.variants.reuse-external-delta-parent = yes
  # benchmark.variants.revs                        = any-1-extra-rev
  # benchmark.variants.source                      = unbundle
  # benchmark.variants.verbosity                   = quiet
with-populate: 0.240157
no-populate:   0.265087  (+10.38%, +0.02)
  # benchmark.variants.revs                        = any-100-extra-rev
with-populate: 1.459518
no-populate:   1.481290   (+1.49%, +0.02)
 ## benchmark.name                                 = hg.command.push
  # benchmark.variants.explicit-rev                = none
  # benchmark.variants.issue6528                   = disabled
  # benchmark.variants.protocol                    = ssh
  # benchmark.variants.reuse-external-delta-parent = yes
  # benchmark.variants.revs                        = any-1-extra-rev
with-populate: 0.771919
no-populate:   0.792025   (+2.60%, +0.02)
  # benchmark.variants.revs                        = any-100-extra-rev
with-populate: 1.459518
no-populate:   1.481290   (+1.49%, +0.02)


For mozilla-try, the "slow down" from pre-populate for small `hg log` is more
visible, but still small in absolute time. (using rust value for the persistent
nodemap value to be relevant).

### data-env-vars.name            = mozilla-try-2019-02-18-ds2-pnm
  # benchmark.name                = hg.command.log
  # bin-env-vars.hg.flavor        = rust
  # benchmark.variants.patch      = yes
  # benchmark.variants.limit-rev  = 1
with-populate: 0.237813
no-populate:   0.229452   (-3.52%, -0.01)
  # benchmark.variants.limit-rev  = 10
  # benchmark.variants.patch      = yes
with-populate: 1.213578
no-populate:   1.205189
### data-env-vars.name            = mozilla-try-2019-02-18-zstd-sparse-revlog
  # benchmark.variants.limit-rev  = 1000
  # benchmark.variants.patch      = no
  # benchmark.variants.rev        = tip
with-populate: 0.198607
no-populate:   0.195038   (-1.80%, -0.00)

However pre-populating provide a significant boost on more complex operations
like unbundle or push:

### data-env-vars.name                             = mozilla-try-2019-02-18-zstd-sparse-revlog
  # benchmark.name                                 = hg.command.push
  # benchmark.variants.explicit-rev                = none
  # benchmark.variants.issue6528                   = disabled
  # benchmark.variants.protocol                    = ssh
  # benchmark.variants.reuse-external-delta-parent = yes
  # benchmark.variants.revs                        = any-1-extra-rev
with-populate: 4.798632
no-populate:   4.953295   (+3.22%, +0.15)
  # benchmark.variants.revs                        = any-100-extra-rev
with-populate: 4.903618
no-populate:   5.014963   (+2.27%, +0.11)
 ## benchmark.name                                 = hg.command.unbundle
  # benchmark.variants.revs                        = any-1-extra-rev
with-populate: 1.423411
no-populate:   1.585365  (+11.38%, +0.16)
  # benchmark.variants.revs                        = any-100-extra-rev
with-populate: 1.537909
no-populate:   1.688489   (+9.79%, +0.15)

============================================
Testing various race condition while pushing
============================================

  $ cat << EOF >> $HGRCPATH
  > [command-templates]
  > log={rev}:{node|short} {desc|firstline} {bookmarks}
  > [ui]
  > timeout = 20
  > [phases]
  > publish=False
  > EOF

Initial Setup
=============

  $ hg init dst
  $ echo a > dst/a-file
  $ hg --cwd dst add a-file
  $ hg --cwd dst commit -m root
  $ hg --cwd dst bookmark my-book
  $ hg --cwd dst bookmarks
   * my-book                   0:a64e49638499
  $ hg --cwd dst log -G
  @  0:a64e49638499 root my-book
  

  $ hg clone ssh://user@dummy/dst src
  requesting all changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 1 changes to 1 files
  new changesets a64e49638499 (1 drafts)
  updating to branch default
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg --cwd src update my-book
  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (activating bookmark my-book)
  $ hg --cwd src log -G
  @  0:a64e49638499 root my-book
  

  $ echo b > src/a-file
  $ hg --cwd src commit -m cA0_
  $ hg --cwd src log -G
  @  1:e89d3a6ed79b cA0_ my-book
  |
  o  0:a64e49638499 root
  

Race condition while pushing a forward moving bookmarks
=======================================================

This is currently slightly broken as we eventually don't push the bookmark.
However at least we do not delete the remote one.

  $ echo c > src/a-file
  $ hg --cwd src push -B my-book --config hooks.prelock="hg commit -m cA1_"
  pushing to ssh://user@dummy/dst
  searching for changes
  remote: adding changesets
  remote: adding manifests
  remote: adding file changes
  remote: added 1 changesets with 1 changes to 1 files
  $ hg --cwd src log -G
  @  2:08d837bbfe8d cA1_ my-book
  |
  o  1:e89d3a6ed79b cA0_
  |
  o  0:a64e49638499 root
  
  $ hg --cwd dst log -G
  o  1:e89d3a6ed79b cA0_
  |
  @  0:a64e49638499 root my-book
  

create a side-moving bookmark
Race condition while pushing a side moving bookmarks
=======================================================

resynchronize the repo and setup test
-------------------------------------

  $ hg --cwd src push -B my-book
  pushing to ssh://user@dummy/dst
  searching for changes
  remote: adding changesets
  remote: adding manifests
  remote: adding file changes
  remote: added 1 changesets with 1 changes to 1 files
  updating bookmark my-book
  $ hg --cwd dst log -G
  o  2:08d837bbfe8d cA1_ my-book
  |
  o  1:e89d3a6ed79b cA0_
  |
  @  0:a64e49638499 root
  

  $ hg --cwd src up 'desc("root")'
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (leaving bookmark my-book)
  $ echo d > src/a-file
  $ hg --cwd src commit -m cB0_
  created new head
  $ hg --cwd src bookmark --force my-book
  $ echo e > src/a-file
  $ hg --cwd src log -G
  @  3:726401661fe5 cB0_ my-book
  |
  | o  2:08d837bbfe8d cA1_
  | |
  | o  1:e89d3a6ed79b cA0_
  |/
  o  0:a64e49638499 root
  

Push the bookmark while a commit is being made
----------------------------------------------

This is currently slightly broken as we eventually don't push the bookmark.
However at least we do not delete the remote one.

  $ hg --cwd src push -f -r 'desc("cB0_")' -B my-book --config hooks.prelock="hg commit -m cB1_"
  pushing to ssh://user@dummy/dst
  searching for changes
  remote: adding changesets
  remote: adding manifests
  remote: adding file changes
  remote: added 1 changesets with 1 changes to 1 files (+1 heads)
  $ hg --cwd src log -G
  @  4:a7f9cbf631a0 cB1_ my-book
  |
  o  3:726401661fe5 cB0_
  |
  | o  2:08d837bbfe8d cA1_
  | |
  | o  1:e89d3a6ed79b cA0_
  |/
  o  0:a64e49638499 root
  

  $ hg --cwd dst log -G
  o  3:726401661fe5 cB0_
  |
  | o  2:08d837bbfe8d cA1_ my-book
  | |
  | o  1:e89d3a6ed79b cA0_
  |/
  @  0:a64e49638499 root