view tests/test-up-local-change.t @ 30442:41a8106789ca

util: implement zstd compression engine

Now that zstd is vendored and being built (in some configurations), we
can implement a compression engine for zstd!

The zstd engine is a little different from existing engines. Because
it may not always be present, we have to defer load the module in case
importing it fails. We facilitate this via a cached property that holds
a reference to the module or None. The "available" method is
implemented to reflect reality.

The zstd engine declares its ability to handle bundles using the
"zstd" human name and the "ZS" internal name. The latter was chosen
because internal names are 2 characters (by only convention I think)
and "ZS" seems reasonable.

The engine, like others, supports specifying the compression level.
However, there are no consumers of this API that yet pass in that
argument. I have plans to change that, so stay tuned.

Since all we need to do to support bundle generation with a new
compression engine is implement and register the compression engine,
bundle generation with zstd "just works!" Tests demonstrating this
have been added.

How does performance of zstd for bundle generation compare? On the
mozilla-unified repo, `hg bundle --all -t <engine>-v2` yields the
following on my i7-6700K on Linux:

engine        CPU time     bundle size   vs orig size   throughput
none            97.0s     4,054,405,584     100.0%       41.8 MB/s
bzip2 (l=9)    393.6s       975,343,098      24.0%       10.3 MB/s
gzip (l=6)     184.0s     1,140,533,074      28.1%       22.0 MB/s
zstd (l=1)     108.2s     1,119,434,718      27.6%       37.5 MB/s
zstd (l=2)     111.3s     1,078,328,002      26.6%       36.4 MB/s
zstd (l=3)     113.7s     1,011,823,727      25.0%       35.7 MB/s
zstd (l=4)     116.0s     1,008,965,888      24.9%       35.0 MB/s
zstd (l=5)     121.0s       977,203,148      24.1%       33.5 MB/s
zstd (l=6)     131.7s       927,360,198      22.9%       30.8 MB/s
zstd (l=7)     139.0s       912,808,505      22.5%       29.2 MB/s
zstd (l=12)    198.1s       854,527,714      21.1%       20.5 MB/s
zstd (l=18)    681.6s       789,750,690      19.5%        5.9 MB/s

On compression, zstd for bundle generation delivers:

* better compression than gzip with significantly less CPU utilization
* better than bzip2 compression ratios while still being significantly
  faster than gzip
* ability to aggressively tune compression level to achieve
  significantly smaller bundles

That last point is important. With clone bundles, a server can
pre-generate a bundle file, upload it to a static file server, and
redirect clients to transparently download it during clone. The server
could choose to produce a zstd bundle with the highest compression
settings possible. This would take a very long time - a magnitude
longer than a typical zstd bundle generation - but the result would
be hundreds of megabytes smaller! For the clone volume we do at
Mozilla, this could translate to petabytes of bandwidth savings
per year and faster clones (due to smaller transfer size).

I don't have detailed numbers to report on decompression. However,
zstd decompression is fast: >1 GB/s output throughput on this machine,
even through the Python bindings. And it can do that regardless of the
compression level of the input. By the time you have enough data to
worry about overhead of decompression, you have plenty of other things
to worry about performance wise.

zstd is wins all around. I can't wait to implement support for it
on the wire protocol and in revlogs.

  $ HGMERGE=true; export HGMERGE

  $ hg init r1
  $ cd r1
  $ echo a > a
  $ hg addremove
  adding a
  $ hg commit -m "1"

  $ hg clone . ../r2
  updating to branch default
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ cd ../r2
  $ hg up
  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ echo abc > a
  $ hg diff --nodates
  diff -r c19d34741b0a a
  --- a/a
  +++ b/a
  @@ -1,1 +1,1 @@
  -a
  +abc

  $ cd ../r1
  $ echo b > b
  $ echo a2 > a
  $ hg addremove
  adding b
  $ hg commit -m "2"

  $ cd ../r2
  $ hg -q pull ../r1
  $ hg status
  M a
  $ hg parents
  changeset:   0:c19d34741b0a
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     1
  
  $ hg --debug up
    searching for copies back to rev 1
    unmatched files in other:
     b
  resolving manifests
   branchmerge: False, force: False, partial: False
   ancestor: c19d34741b0a, local: c19d34741b0a+, remote: 1e71731e6fbb
   preserving a for resolve of a
   b: remote created -> g
  getting b
   a: versions differ -> m (premerge)
  picked tool 'true' for a (binary False symlink False changedelete False)
  merging a
  my a@c19d34741b0a+ other a@1e71731e6fbb ancestor a@c19d34741b0a
   a: versions differ -> m (merge)
  picked tool 'true' for a (binary False symlink False changedelete False)
  my a@c19d34741b0a+ other a@1e71731e6fbb ancestor a@c19d34741b0a
  launching merge tool: true *$TESTTMP/r2/a* * * (glob)
  merge tool returned: 0
  1 files updated, 1 files merged, 0 files removed, 0 files unresolved
  $ hg parents
  changeset:   1:1e71731e6fbb
  tag:         tip
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     2
  
  $ hg --debug up 0
  starting 4 threads for background file closing (?)
    searching for copies back to rev 0
    unmatched files in local (from topological common ancestor):
     b
  resolving manifests
   branchmerge: False, force: False, partial: False
   ancestor: 1e71731e6fbb, local: 1e71731e6fbb+, remote: c19d34741b0a
   preserving a for resolve of a
   b: other deleted -> r
  removing b
  starting 4 threads for background file closing (?)
   a: versions differ -> m (premerge)
  picked tool 'true' for a (binary False symlink False changedelete False)
  merging a
  my a@1e71731e6fbb+ other a@c19d34741b0a ancestor a@1e71731e6fbb
   a: versions differ -> m (merge)
  picked tool 'true' for a (binary False symlink False changedelete False)
  my a@1e71731e6fbb+ other a@c19d34741b0a ancestor a@1e71731e6fbb
  launching merge tool: true *$TESTTMP/r2/a* * * (glob)
  merge tool returned: 0
  0 files updated, 1 files merged, 1 files removed, 0 files unresolved
  $ hg parents
  changeset:   0:c19d34741b0a
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     1
  
  $ hg --debug up
    searching for copies back to rev 1
    unmatched files in other:
     b
  resolving manifests
   branchmerge: False, force: False, partial: False
   ancestor: c19d34741b0a, local: c19d34741b0a+, remote: 1e71731e6fbb
   preserving a for resolve of a
   b: remote created -> g
  getting b
   a: versions differ -> m (premerge)
  picked tool 'true' for a (binary False symlink False changedelete False)
  merging a
  my a@c19d34741b0a+ other a@1e71731e6fbb ancestor a@c19d34741b0a
   a: versions differ -> m (merge)
  picked tool 'true' for a (binary False symlink False changedelete False)
  my a@c19d34741b0a+ other a@1e71731e6fbb ancestor a@c19d34741b0a
  launching merge tool: true *$TESTTMP/r2/a* * * (glob)
  merge tool returned: 0
  1 files updated, 1 files merged, 0 files removed, 0 files unresolved
  $ hg parents
  changeset:   1:1e71731e6fbb
  tag:         tip
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     2
  
  $ hg -v history
  changeset:   1:1e71731e6fbb
  tag:         tip
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  files:       a b
  description:
  2
  
  
  changeset:   0:c19d34741b0a
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  files:       a
  description:
  1
  
  
  $ hg diff --nodates
  diff -r 1e71731e6fbb a
  --- a/a
  +++ b/a
  @@ -1,1 +1,1 @@
  -a2
  +abc


create a second head

  $ cd ../r1
  $ hg up 0
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved
  $ echo b2 > b
  $ echo a3 > a
  $ hg addremove
  adding b
  $ hg commit -m "3"
  created new head

  $ cd ../r2
  $ hg -q pull ../r1
  $ hg status
  M a
  $ hg parents
  changeset:   1:1e71731e6fbb
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     2
  
  $ hg --debug up
  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
  1 other heads for branch "default"

test conflicting untracked files

  $ hg up -qC 0
  $ echo untracked > b
  $ hg st
  ? b
  $ hg up 1
  b: untracked file differs
  abort: untracked files in working directory differ from files in requested revision
  [255]
  $ rm b

test conflicting untracked ignored file

  $ hg up -qC 0
  $ echo ignored > .hgignore
  $ hg add .hgignore
  $ hg ci -m 'add .hgignore'
  created new head
  $ echo ignored > ignored
  $ hg add ignored
  $ hg ci -m 'add ignored file'

  $ hg up -q 'desc("add .hgignore")'
  $ echo untracked > ignored
  $ hg st
  $ hg up 'desc("add ignored file")'
  ignored: untracked file differs
  abort: untracked files in working directory differ from files in requested revision
  [255]

test a local add

  $ cd ..
  $ hg init a
  $ hg init b
  $ echo a > a/a
  $ echo a > b/a
  $ hg --cwd a commit -A -m a
  adding a
  $ cd b
  $ hg add a
  $ hg pull -u ../a
  pulling from ../a
  requesting all changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 1 changes to 1 files
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg st

test updating backwards through a rename

  $ hg mv a b
  $ hg ci -m b
  $ echo b > b
  $ hg up -q 0
  $ hg st
  M a
  $ hg diff --nodates
  diff -r cb9a9f314b8b a
  --- a/a
  +++ b/a
  @@ -1,1 +1,1 @@
  -a
  +b

test for superfluous filemerge of clean files renamed in the past

  $ hg up -qC tip
  $ echo c > c
  $ hg add c
  $ hg up -qt:fail 0

  $ cd ..