view tests/test-status-tracked-key.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)

===============================
Test the "tracked hint" feature
===============================

The tracked hint feature provide a file that get updated when the set of tracked
files get updated.

basic setup

  $ cat << EOF >> $HGRCPATH
  > [format]
  > use-dirstate-tracked-hint=yes
  > EOF

  $ hg init tracked-hint-test
  $ cd tracked-hint-test
  $ hg debugbuilddag '.+10' -n
  $ hg log -G -T '{rev} {desc} {files}\n'
  o  10 r10 nf10
  |
  o  9 r9 nf9
  |
  o  8 r8 nf8
  |
  o  7 r7 nf7
  |
  o  6 r6 nf6
  |
  o  5 r5 nf5
  |
  o  4 r4 nf4
  |
  o  3 r3 nf3
  |
  o  2 r2 nf2
  |
  o  1 r1 nf1
  |
  o  0 r0 nf0
  
  $ hg up tip
  11 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg files
  nf0
  nf1
  nf10
  nf2
  nf3
  nf4
  nf5
  nf6
  nf7
  nf8
  nf9

key-file exists
-----------

The tracked hint file should exist

  $ ls -1 .hg/dirstate*
  .hg/dirstate
  .hg/dirstate-tracked-hint

key-file stay the same if the tracked set is unchanged
------------------------------------------------------

(copy its content for later comparison)

  $ cp .hg/dirstate-tracked-hint ../key-bck
  $ echo foo >> nf0
  $ sleep 1
  $ hg status
  M nf0
  $ diff --brief .hg/dirstate-tracked-hint ../key-bck
  $ hg revert -C nf0
  $ sleep 1
  $ hg status
  $ diff --brief .hg/dirstate-tracked-hint ../key-bck

key-file change if the tracked set is changed manually
------------------------------------------------------

adding a file to tracking

  $ cp .hg/dirstate-tracked-hint ../key-bck
  $ echo x > x
  $ hg add x
  $ diff --brief .hg/dirstate-tracked-hint ../key-bck
  Files .hg/dirstate-tracked-hint and ../key-bck differ
  [1]

remove a file from tracking
(forget)

  $ cp .hg/dirstate-tracked-hint ../key-bck
  $ hg forget x
  $ diff --brief .hg/dirstate-tracked-hint ../key-bck
  Files .hg/dirstate-tracked-hint and ../key-bck differ
  [1]

(remove)

  $ cp .hg/dirstate-tracked-hint ../key-bck
  $ hg remove nf1
  $ diff --brief .hg/dirstate-tracked-hint ../key-bck
  Files .hg/dirstate-tracked-hint and ../key-bck differ
  [1]

key-file changes on revert (when applicable)
--------------------------------------------

  $ cp .hg/dirstate-tracked-hint ../key-bck
  $ hg status
  R nf1
  ? x
  $ hg revert --all
  undeleting nf1
  $ hg status
  ? x
  $ diff --brief .hg/dirstate-tracked-hint ../key-bck
  Files .hg/dirstate-tracked-hint and ../key-bck differ
  [1]


`hg update` does affect the key-file (when needed)
--------------------------------------------------

update changing the tracked set

(removing)

  $ cp .hg/dirstate-tracked-hint ../key-bck
  $ hg status --rev . --rev '.#generations[-1]'
  R nf10
  $ hg up '.#generations[-1]'
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
  $ diff --brief .hg/dirstate-tracked-hint ../key-bck
  Files .hg/dirstate-tracked-hint and ../key-bck differ
  [1]

(adding)

  $ cp .hg/dirstate-tracked-hint ../key-bck
  $ hg status --rev . --rev '.#generations[1]'
  A nf10
  $ hg up '.#generations[1]'
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ diff --brief .hg/dirstate-tracked-hint ../key-bck
  Files .hg/dirstate-tracked-hint and ../key-bck differ
  [1]

update not affecting the tracked set

  $ echo foo >> nf0
  $ hg commit -m foo

  $ cp .hg/dirstate-tracked-hint ../key-bck
  $ hg status --rev . --rev '.#generations[-1]'
  M nf0
  $ hg up '.#generations[-1]'
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ diff --brief .hg/dirstate-tracked-hint ../key-bck

Test upgrade and downgrade
==========================

  $ test -f .hg/dirstate-tracked-hint
  $ hg debugrequires | grep 'tracked'
  dirstate-tracked-key-v1

downgrade

  $ hg debugupgraderepo --config format.use-dirstate-tracked-hint=no --run --quiet
  upgrade will perform the following actions:
  
  requirements
     preserved: * (glob)
     removed: dirstate-tracked-key-v1
  
  no revlogs to process
  
  $ test -f .hg/dirstate-tracked-hint
  [1]
  $ hg debugrequires | grep 'tracked'
  [1]

upgrade

  $ hg debugupgraderepo --config format.use-dirstate-tracked-hint=yes --run --quiet
  upgrade will perform the following actions:
  
  requirements
     preserved: * (glob)
     added: dirstate-tracked-key-v1
  
  no revlogs to process
  
  $ test -f .hg/dirstate-tracked-hint
  $ hg debugrequires | grep 'tracked'
  dirstate-tracked-key-v1
  $ cd ..

Test automatic upgrade and downgrade
------------------------------------

create an initial repository

  $ hg init auto-upgrade \
  > --config format.use-dirstate-tracked-hint=no
  $ hg debugbuilddag -R auto-upgrade --new-file .+5
  $ hg -R auto-upgrade update
  6 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg debugformat -R auto-upgrade | grep tracked
  tracked-hint:        no

upgrade it to dirstate-tracked-hint automatically

  $ hg status -R auto-upgrade \
  > --config format.use-dirstate-tracked-hint.automatic-upgrade-of-mismatching-repositories=yes \
  > --config format.use-dirstate-tracked-hint=yes
  automatically upgrading repository to the `tracked-hint` feature
  (see `hg help config.format.use-dirstate-tracked-hint` for details)
  $ hg debugformat -R auto-upgrade | grep tracked
  tracked-hint:       yes

rhg supports this feature

  $ hg status -R auto-upgrade \
  > --config format.use-dirstate-tracked-hint=yes --config rhg.on-unsupported=abort

downgrade it from dirstate-tracked-hint automatically

  $ hg status -R auto-upgrade \
  > --config format.use-dirstate-tracked-hint.automatic-upgrade-of-mismatching-repositories=yes \
  > --config format.use-dirstate-tracked-hint=no
  automatically downgrading repository from the `tracked-hint` feature
  (see `hg help config.format.use-dirstate-tracked-hint` for details)
  $ hg debugformat -R auto-upgrade | grep tracked
  tracked-hint:        no