view tests/test-subrepo-missing.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.

  $ hg init repo
  $ cd repo
  $ hg init subrepo
  $ echo a > subrepo/a
  $ hg -R subrepo ci -Am adda
  adding a
  $ echo 'subrepo = subrepo' > .hgsub
  $ hg ci -Am addsubrepo
  adding .hgsub
  $ echo b > subrepo/b
  $ hg -R subrepo ci -Am addb
  adding b
  $ hg ci -m updatedsub

ignore blanklines in .hgsubstate

  >>> file('.hgsubstate', 'wb').write('\n\n   \t \n   \n')
  $ hg st --subrepos
  M .hgsubstate
  $ hg revert -qC .hgsubstate

abort more gracefully on .hgsubstate parsing error

  $ cp .hgsubstate .hgsubstate.old
  >>> file('.hgsubstate', 'wb').write('\ninvalid')
  $ hg st --subrepos --cwd $TESTTMP -R $TESTTMP/repo
  abort: invalid subrepository revision specifier in 'repo/.hgsubstate' line 2
  [255]
  $ mv .hgsubstate.old .hgsubstate

delete .hgsub and revert it

  $ rm .hgsub
  $ hg revert .hgsub
  warning: subrepo spec file '.hgsub' not found
  warning: subrepo spec file '.hgsub' not found
  warning: subrepo spec file '.hgsub' not found

delete .hgsubstate and revert it

  $ rm .hgsubstate
  $ hg revert .hgsubstate

delete .hgsub and update

  $ rm .hgsub
  $ hg up 0 --cwd $TESTTMP -R $TESTTMP/repo
  warning: subrepo spec file 'repo/.hgsub' not found
  warning: subrepo spec file 'repo/.hgsub' not found
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg st
  warning: subrepo spec file '.hgsub' not found
  ! .hgsub
  $ ls subrepo
  a

delete .hgsubstate and update

  $ hg up -C
  warning: subrepo spec file '.hgsub' not found
  warning: subrepo spec file '.hgsub' not found
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ rm .hgsubstate
  $ hg up 0
  other [destination] changed .hgsubstate which local [working copy] deleted
  use (c)hanged version or leave (d)eleted? c
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg st
  $ ls subrepo
  a

Enable obsolete

  $ cat >> $HGRCPATH << EOF
  > [ui]
  > logtemplate= {rev}:{node|short} {desc|firstline}
  > [phases]
  > publish=False
  > [experimental]
  > evolution=createmarkers
  > EOF

check that we can update parent repo with missing (amended) subrepo revision

  $ hg up --repository subrepo -r tip
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg ci -m "updated subrepo to tip"
  created new head
  $ cd subrepo
  $ hg update -r tip
  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ echo foo > a
  $ hg commit --amend -m "addb (amended)"
  $ cd ..
  $ hg update --clean .
  revision 102a90ea7b4a in subrepo subrepo is hidden
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved

check that --hidden is propagated to the subrepo

  $ hg -R subrepo up tip
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg ci -m 'commit with amended subrepo'
  $ echo bar > subrepo/a
  $ hg -R subrepo ci --amend -m "amend a (again)"
  $ hg --hidden cat subrepo/a
  foo

verify will warn if locked-in subrepo revisions are hidden or missing

  $ hg ci -m "amended subrepo (again)"
  $ hg --config extensions.strip= --hidden strip -R subrepo -qr 'tip'
  $ hg verify
  checking changesets
  checking manifests
  crosschecking files in changesets and manifests
  checking files
  2 files, 5 changesets, 5 total revisions
  checking subrepo links
  subrepo 'subrepo' is hidden in revision a66de08943b6
  subrepo 'subrepo' is hidden in revision 674d05939c1e
  subrepo 'subrepo' not found in revision a7d05d9055a4

verifying shouldn't init a new subrepo if the reference doesn't exist

  $ mv subrepo b
  $ hg verify
  checking changesets
  checking manifests
  crosschecking files in changesets and manifests
  checking files
  2 files, 5 changesets, 5 total revisions
  checking subrepo links
  0: repository $TESTTMP/repo/subrepo not found (glob)
  1: repository $TESTTMP/repo/subrepo not found (glob)
  3: repository $TESTTMP/repo/subrepo not found (glob)
  4: repository $TESTTMP/repo/subrepo not found (glob)
  $ ls
  b
  $ mv b subrepo

  $ cd ..