view tests/test-rebase-rename.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.

  $ cat >> $HGRCPATH <<EOF
  > [extensions]
  > rebase=
  > 
  > [alias]
  > tlog  = log  --template "{rev}: '{desc}' {branches}\n"
  > tglog = tlog --graph
  > EOF


  $ hg init a
  $ cd a

  $ mkdir d
  $ echo a > a
  $ hg ci -Am A
  adding a

  $ echo b > d/b
  $ hg ci -Am B
  adding d/b

  $ hg mv d d-renamed
  moving d/b to d-renamed/b (glob)
  $ hg ci -m 'rename B'

  $ hg up -q -C 1

  $ hg mv a a-renamed
  $ echo x > d/x
  $ hg add d/x

  $ hg ci -m 'rename A'
  created new head

  $ hg tglog
  @  3: 'rename A'
  |
  | o  2: 'rename B'
  |/
  o  1: 'B'
  |
  o  0: 'A'
  

Rename is tracked:

  $ hg tlog -p --git -r tip
  3: 'rename A' 
  diff --git a/a b/a-renamed
  rename from a
  rename to a-renamed
  diff --git a/d/x b/d/x
  new file mode 100644
  --- /dev/null
  +++ b/d/x
  @@ -0,0 +1,1 @@
  +x
  
Rebase the revision containing the rename:

  $ hg rebase -s 3 -d 2
  rebasing 3:73a3ee40125d "rename A" (tip)
  saved backup bundle to $TESTTMP/a/.hg/strip-backup/73a3ee40125d-1d78ebcf-backup.hg (glob)

  $ hg tglog
  @  3: 'rename A'
  |
  o  2: 'rename B'
  |
  o  1: 'B'
  |
  o  0: 'A'
  

Rename is not lost:

  $ hg tlog -p --git -r tip
  3: 'rename A' 
  diff --git a/a b/a-renamed
  rename from a
  rename to a-renamed
  diff --git a/d-renamed/x b/d-renamed/x
  new file mode 100644
  --- /dev/null
  +++ b/d-renamed/x
  @@ -0,0 +1,1 @@
  +x
  

Rebased revision does not contain information about b (issue3739)

  $ hg log -r 3 --debug
  changeset:   3:032a9b75e83bff1dcfb6cbfa4ef50a704bf1b569
  tag:         tip
  phase:       draft
  parent:      2:220d0626d185f372d9d8f69d9c73b0811d7725f7
  parent:      -1:0000000000000000000000000000000000000000
  manifest:    3:035d66b27a1b06b2d12b46d41a39adb7a200c370
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  files+:      a-renamed d-renamed/x
  files-:      a
  extra:       branch=default
  extra:       rebase_source=73a3ee40125d6f0f347082e5831ceccb3f005f8a
  description:
  rename A
  
  

  $ cd ..


  $ hg init b
  $ cd b

  $ echo a > a
  $ hg ci -Am A
  adding a

  $ echo b > b
  $ hg ci -Am B
  adding b

  $ hg cp b b-copied
  $ hg ci -Am 'copy B'

  $ hg up -q -C 1

  $ hg cp a a-copied
  $ hg ci -m 'copy A'
  created new head

  $ hg tglog
  @  3: 'copy A'
  |
  | o  2: 'copy B'
  |/
  o  1: 'B'
  |
  o  0: 'A'
  
Copy is tracked:

  $ hg tlog -p --git -r tip
  3: 'copy A' 
  diff --git a/a b/a-copied
  copy from a
  copy to a-copied
  
Rebase the revision containing the copy:

  $ hg rebase -s 3 -d 2
  rebasing 3:0a8162ff18a8 "copy A" (tip)
  saved backup bundle to $TESTTMP/b/.hg/strip-backup/0a8162ff18a8-dd06302a-backup.hg (glob)

  $ hg tglog
  @  3: 'copy A'
  |
  o  2: 'copy B'
  |
  o  1: 'B'
  |
  o  0: 'A'
  

Copy is not lost:

  $ hg tlog -p --git -r tip
  3: 'copy A' 
  diff --git a/a b/a-copied
  copy from a
  copy to a-copied
  

Rebased revision does not contain information about b (issue3739)

  $ hg log -r 3 --debug
  changeset:   3:98f6e6dbf45ab54079c2237fbd11066a5c41a11d
  tag:         tip
  phase:       draft
  parent:      2:39e588434882ff77d01229d169cdc77f29e8855e
  parent:      -1:0000000000000000000000000000000000000000
  manifest:    3:2232f329d66fffe3930d43479ae624f66322b04d
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  files+:      a-copied
  extra:       branch=default
  extra:       rebase_source=0a8162ff18a8900df8df8ef7ac0046955205613e
  description:
  copy A
  
  

  $ cd ..


Test rebase across repeating renames:

  $ hg init repo

  $ cd repo

  $ echo testing > file1.txt
  $ hg add file1.txt
  $ hg ci -m "Adding file1"

  $ hg rename file1.txt file2.txt
  $ hg ci -m "Rename file1 to file2"

  $ echo Unrelated change > unrelated.txt
  $ hg add unrelated.txt
  $ hg ci -m "Unrelated change"

  $ hg rename file2.txt file1.txt
  $ hg ci -m "Rename file2 back to file1"

  $ hg update -r -2
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved

  $ echo Another unrelated change >> unrelated.txt
  $ hg ci -m "Another unrelated change"
  created new head

  $ hg tglog
  @  4: 'Another unrelated change'
  |
  | o  3: 'Rename file2 back to file1'
  |/
  o  2: 'Unrelated change'
  |
  o  1: 'Rename file1 to file2'
  |
  o  0: 'Adding file1'
  

  $ hg rebase -s 4 -d 3
  rebasing 4:b918d683b091 "Another unrelated change" (tip)
  saved backup bundle to $TESTTMP/repo/.hg/strip-backup/b918d683b091-3024bc57-backup.hg (glob)

  $ hg diff --stat -c .
   unrelated.txt |  1 +
   1 files changed, 1 insertions(+), 0 deletions(-)

  $ cd ..

Verify that copies get preserved (issue4192).
  $ hg init copy-gets-preserved
  $ cd copy-gets-preserved

  $ echo a > a
  $ hg add a
  $ hg commit --message "File a created"
  $ hg copy a b
  $ echo b > b
  $ hg commit --message "File b created as copy of a and modified"
  $ hg copy b c
  $ echo c > c
  $ hg commit --message "File c created as copy of b and modified"
  $ hg copy c d
  $ echo d > d
  $ hg commit --message "File d created as copy of c and modified"

Note that there are four entries in the log for d
  $ hg tglog --follow d
  @  3: 'File d created as copy of c and modified'
  |
  o  2: 'File c created as copy of b and modified'
  |
  o  1: 'File b created as copy of a and modified'
  |
  o  0: 'File a created'
  
Update back to before we performed copies, and inject an unrelated change.
  $ hg update 0
  0 files updated, 0 files merged, 3 files removed, 0 files unresolved

  $ echo unrelated > unrelated
  $ hg add unrelated
  $ hg commit --message "Unrelated file created"
  created new head
  $ hg update 4
  0 files updated, 0 files merged, 0 files removed, 0 files unresolved

Rebase the copies on top of the unrelated change.
  $ hg rebase --source 1 --dest 4
  rebasing 1:79d255d24ad2 "File b created as copy of a and modified"
  rebasing 2:327f772bc074 "File c created as copy of b and modified"
  rebasing 3:421b7e82bb85 "File d created as copy of c and modified"
  saved backup bundle to $TESTTMP/copy-gets-preserved/.hg/strip-backup/79d255d24ad2-a2265555-backup.hg (glob)
  $ hg update 4
  3 files updated, 0 files merged, 0 files removed, 0 files unresolved

There should still be four entries in the log for d
  $ hg tglog --follow d
  @  4: 'File d created as copy of c and modified'
  |
  o  3: 'File c created as copy of b and modified'
  |
  o  2: 'File b created as copy of a and modified'
  :
  o  0: 'File a created'
  
Same steps as above, but with --collapse on rebase to make sure the
copy records collapse correctly.
  $ hg co 1
  0 files updated, 0 files merged, 3 files removed, 0 files unresolved
  $ echo more >> unrelated
  $ hg ci -m 'unrelated commit is unrelated'
  created new head
  $ hg rebase -s 2 --dest 5 --collapse
  rebasing 2:68bf06433839 "File b created as copy of a and modified"
  rebasing 3:af74b229bc02 "File c created as copy of b and modified"
  merging b and c to c
  rebasing 4:dbb9ba033561 "File d created as copy of c and modified"
  merging c and d to d
  saved backup bundle to $TESTTMP/copy-gets-preserved/.hg/strip-backup/68bf06433839-dde37595-backup.hg (glob)
  $ hg co tip
  3 files updated, 0 files merged, 0 files removed, 0 files unresolved

This should show both revision 3 and 0 since 'd' was transitively a
copy of 'a'.

  $ hg tglog --follow d
  @  3: 'Collapsed revision
  :  * File b created as copy of a and modified
  :  * File c created as copy of b and modified
  :  * File d created as copy of c and modified'
  o  0: 'File a created'
  

  $ cd ..