view tests/test-split-legacy-inline-changelog.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 operation on repository with an inlined changelog
======================================================

Inlined revlog has been a bag of complexity for a long time and the combination
with special transaction logic on the changelog was a long source of bugs
poorly covered by the test suites.

We stopped doing any usage of inlined-revlog for changelog in a93e52f0b6ff,
upgrading legacy inlined version as soon as possible when we see them. However
this Mercurial does not produce such inlined-changelog that case is very poorly
covered in the test suites. This test file aims at covering these cases.

Double checking test data
=========================

We should have a repository around

  $ mkdir sanity-check
  $ cd sanity-check
  $ tar xf $TESTDIR/bundles/inlined-changelog.tar
  $ cd inlined-changelog
  $ hg root
  $TESTTMP/sanity-check/inlined-changelog

The repository should not be corrupted initially

  $ hg verify
  checking changesets
  checking manifests
  crosschecking files in changesets and manifests
  checking files
  checking dirstate
  checked 1 changesets with 1 changes to 1 files

The changelog of that repository MUST be inlined

  $ hg debugrevlog -c | grep -E '^flags\b'
  flags  : inline

Touching that repository MUST split that inlined changelog

  $ hg branch foo --quiet
  $ hg commit -m foo --quiet
  $ hg debugrevlog -c | grep -E '^flags\b'
  flags  : (none)

  $ cd ../..

Test doing a simple commit
==========================

Simple commit
-------------

  $ mkdir simple-commit
  $ cd simple-commit
  $ tar xf $TESTDIR/bundles/inlined-changelog.tar
  $ cd inlined-changelog
  $ hg up --quiet
  $ hg log -GT '[{rev}] {desc}\n'
  @  [0] first commit
  
  $ echo b > b
  $ hg add b
  $ hg commit -m "second changeset"
  $ hg verify
  checking changesets
  checking manifests
  crosschecking files in changesets and manifests
  checking files
  checking dirstate
  checked 2 changesets with 2 changes to 2 files
  $ hg log -GT '[{rev}] {desc}\n'
  @  [1] second changeset
  |
  o  [0] first commit
  
  $ cd ../..

Simple commit with a pretxn hook configured
-------------------------------------------

Before 6.7.3 this used to delete the changelog index

  $ mkdir pretxnclose-commit
  $ cd pretxnclose-commit
  $ tar xf $TESTDIR/bundles/inlined-changelog.tar
  $ cat >> inlined-changelog/.hg/hgrc <<EOF
  > [hooks]
  > pretxnclose=hg log -r tip -T "pre-txn tip rev: {rev}\n"
  > EOF
  $ cd inlined-changelog
  $ hg up --quiet
  $ hg log -GT '[{rev}] {desc}\n'
  @  [0] first commit
  
  $ echo b > b
  $ hg add b
  $ hg commit -m "second changeset"
  pre-txn tip rev: 1
  $ hg verify
  checking changesets
  checking manifests
  crosschecking files in changesets and manifests
  checking files
  checking dirstate
  checked 2 changesets with 2 changes to 2 files
  $ hg log -GT '[{rev}] {desc}\n'
  @  [1] second changeset
  |
  o  [0] first commit
  
  $ cd ../..

Test pushing to a repository with a repository revlog
=====================================================

Simple local push
-----------------

  $ mkdir simple-local-push
  $ cd simple-local-push
  $ tar xf $TESTDIR/bundles/inlined-changelog.tar
  $ hg log -R inlined-changelog -T '[{rev}] {desc}\n'
  [0] first commit

  $ hg clone --pull inlined-changelog client
  requesting all changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 1 changes to 1 files
  new changesets 827f11bfd362
  updating to branch default
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ cd client
  $ echo b > b
  $ hg add b
  $ hg commit -m "second changeset"
  $ hg push
  pushing to $TESTTMP/*/inlined-changelog (glob)
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 1 changes to 1 files
  $ cd ..

  $ hg verify -R inlined-changelog
  checking changesets
  checking manifests
  crosschecking files in changesets and manifests
  checking files
  checking dirstate
  checked 2 changesets with 2 changes to 2 files
  $ hg log -R inlined-changelog -T '[{rev}] {desc}\n'
  [1] second changeset
  [0] first commit
  $ cd ..

Simple local push with a pretxnchangegroup hook
-----------------------------------------------

Before 6.7.3 this used to delete the server changelog

  $ mkdir pretxnchangegroup-local-push
  $ cd pretxnchangegroup-local-push
  $ tar xf $TESTDIR/bundles/inlined-changelog.tar
  $ cat >> inlined-changelog/.hg/hgrc <<EOF
  > [hooks]
  > pretxnchangegroup=hg log -r tip -T "pre-txn tip rev: {rev}\n"
  > EOF
  $ hg log -R inlined-changelog -T '[{rev}] {desc}\n'
  [0] first commit

  $ hg clone --pull inlined-changelog client
  requesting all changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 1 changes to 1 files
  new changesets 827f11bfd362
  updating to branch default
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ cd client
  $ echo b > b
  $ hg add b
  $ hg commit -m "second changeset"
  $ hg push
  pushing to $TESTTMP/*/inlined-changelog (glob)
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  pre-txn tip rev: 1
  added 1 changesets with 1 changes to 1 files
  $ cd ..

  $ hg verify -R inlined-changelog
  checking changesets
  checking manifests
  crosschecking files in changesets and manifests
  checking files
  checking dirstate
  checked 2 changesets with 2 changes to 2 files
  $ hg log -R inlined-changelog -T '[{rev}] {desc}\n'
  [1] second changeset
  [0] first commit
  $ cd ..

Simple ssh push
-----------------

  $ mkdir simple-ssh-push
  $ cd simple-ssh-push
  $ tar xf $TESTDIR/bundles/inlined-changelog.tar
  $ hg log -R inlined-changelog -T '[{rev}] {desc}\n'
  [0] first commit

  $ hg clone ssh://user@dummy/"`pwd`"/inlined-changelog client
  requesting all changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 1 changes to 1 files
  new changesets 827f11bfd362
  updating to branch default
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ cd client
  $ echo b > b
  $ hg add b
  $ hg commit -m "second changeset"
  $ hg push
  pushing to ssh://user@dummy/$TESTTMP/simple-ssh-push/inlined-changelog
  searching for changes
  remote: adding changesets
  remote: adding manifests
  remote: adding file changes
  remote: added 1 changesets with 1 changes to 1 files
  $ cd ..

  $ hg verify -R inlined-changelog
  checking changesets
  checking manifests
  crosschecking files in changesets and manifests
  checking files
  checking dirstate
  checked 2 changesets with 2 changes to 2 files
  $ hg log -R inlined-changelog -T '[{rev}] {desc}\n'
  [1] second changeset
  [0] first commit
  $ cd ..

Simple ssh push with a pretxnchangegroup hook
-----------------------------------------------

Before 6.7.3 this used to delete the server changelog

  $ mkdir pretxnchangegroup-ssh-push
  $ cd pretxnchangegroup-ssh-push
  $ tar xf $TESTDIR/bundles/inlined-changelog.tar
  $ cat >> inlined-changelog/.hg/hgrc <<EOF
  > [hooks]
  > pretxnchangegroup=hg log -r tip -T "pre-txn tip rev: {rev}\n"
  > EOF
  $ hg log -R inlined-changelog -T '[{rev}] {desc}\n'
  [0] first commit

  $ hg clone ssh://user@dummy/"`pwd`"/inlined-changelog client
  requesting all changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 1 changes to 1 files
  new changesets 827f11bfd362
  updating to branch default
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ cd client
  $ echo b > b
  $ hg add b
  $ hg commit -m "second changeset"
  $ hg push
  pushing to ssh://user@dummy/$TESTTMP/pretxnchangegroup-ssh-push/inlined-changelog
  searching for changes
  remote: adding changesets
  remote: adding manifests
  remote: adding file changes
  remote: pre-txn tip rev: 1
  remote: added 1 changesets with 1 changes to 1 files
  $ cd ..

  $ hg verify -R inlined-changelog
  checking changesets
  checking manifests
  crosschecking files in changesets and manifests
  checking files
  checking dirstate
  checked 2 changesets with 2 changes to 2 files
  $ hg log -R inlined-changelog -T '[{rev}] {desc}\n'
  [1] second changeset
  [0] first commit
  $ cd ..