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view tests/test-rollback.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.
author | Gregory Szorc <gregory.szorc@gmail.com> |
---|---|
date | Fri, 11 Nov 2016 01:10:07 -0800 |
parents | fe50341de1ff |
children | 3ed26ba54685 |
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setup repo $ hg init t $ cd t $ echo a > a $ hg commit -Am'add a' adding a $ hg verify checking changesets checking manifests crosschecking files in changesets and manifests checking files 1 files, 1 changesets, 1 total revisions $ hg parents changeset: 0:1f0dee641bb7 tag: tip user: test date: Thu Jan 01 00:00:00 1970 +0000 summary: add a rollback to null revision $ hg status $ hg rollback repository tip rolled back to revision -1 (undo commit) working directory now based on revision -1 $ hg verify checking changesets checking manifests crosschecking files in changesets and manifests checking files 0 files, 0 changesets, 0 total revisions $ hg parents $ hg status A a Two changesets this time so we rollback to a real changeset $ hg commit -m'add a again' $ echo a >> a $ hg commit -m'modify a' Test issue 902 (current branch is preserved) $ hg branch test marked working directory as branch test (branches are permanent and global, did you want a bookmark?) $ hg rollback repository tip rolled back to revision 0 (undo commit) working directory now based on revision 0 $ hg branch default Test issue 1635 (commit message saved) $ cat .hg/last-message.txt ; echo modify a Test rollback of hg before issue 902 was fixed $ hg commit -m "test3" $ hg branch test marked working directory as branch test (branches are permanent and global, did you want a bookmark?) $ rm .hg/undo.branch $ hg rollback repository tip rolled back to revision 0 (undo commit) named branch could not be reset: current branch is still 'test' working directory now based on revision 0 $ hg branch test working dir unaffected by rollback: do not restore dirstate et. al. $ hg log --template '{rev} {branch} {desc|firstline}\n' 0 default add a again $ hg status M a $ hg bookmark foo $ hg commit -m'modify a again' $ echo b > b $ hg bookmark bar -r default #making bar active, before the transaction $ hg commit -Am'add b' adding b $ hg log --template '{rev} {branch} {desc|firstline}\n' 2 test add b 1 test modify a again 0 default add a again $ hg update bar 1 files updated, 0 files merged, 1 files removed, 0 files unresolved (activating bookmark bar) $ cat .hg/undo.branch ; echo test $ hg rollback -f repository tip rolled back to revision 1 (undo commit) $ hg id -n 0 $ hg branch default $ cat .hg/bookmarks.current ; echo bar $ hg bookmark --delete foo bar rollback by pretxncommit saves commit message (issue1635) $ echo a >> a $ hg --config hooks.pretxncommit=false commit -m"precious commit message" transaction abort! rollback completed abort: pretxncommit hook exited with status * (glob) [255] $ cat .hg/last-message.txt ; echo precious commit message same thing, but run $EDITOR $ cat > editor.sh << '__EOF__' > echo "another precious commit message" > "$1" > __EOF__ $ HGEDITOR="\"sh\" \"`pwd`/editor.sh\"" hg --config hooks.pretxncommit=false commit 2>&1 note: commit message saved in .hg/last-message.txt transaction abort! rollback completed abort: pretxncommit hook exited with status * (glob) [255] $ cat .hg/last-message.txt another precious commit message test rollback on served repository #if serve $ hg commit -m "precious commit message" $ hg serve -p $HGPORT -d --pid-file=hg.pid -A access.log -E errors.log $ cat hg.pid >> $DAEMON_PIDS $ cd .. $ hg clone http://localhost:$HGPORT u requesting all changes adding changesets adding manifests adding file changes added 3 changesets with 2 changes to 1 files (+1 heads) updating to branch default 1 files updated, 0 files merged, 0 files removed, 0 files unresolved $ cd u $ hg id default 068774709090 now rollback and observe that 'hg serve' reloads the repository and presents the correct tip changeset: $ hg -R ../t rollback repository tip rolled back to revision 1 (undo commit) working directory now based on revision 0 $ hg id default 791dd2169706 #endif update to older changeset and then refuse rollback, because that would lose data (issue2998) $ cd ../t $ hg -q update $ rm `hg status -un` $ template='{rev}:{node|short} [{branch}] {desc|firstline}\n' $ echo 'valuable new file' > b $ echo 'valuable modification' >> a $ hg commit -A -m'a valuable change' adding b $ hg update 0 1 files updated, 0 files merged, 1 files removed, 0 files unresolved $ hg rollback abort: rollback of last commit while not checked out may lose data (use -f to force) [255] $ hg tip -q 2:4d9cd3795eea $ hg rollback -f repository tip rolled back to revision 1 (undo commit) $ hg status $ hg log --removed b # yep, it's gone same again, but emulate an old client that doesn't write undo.desc $ hg -q update $ echo 'valuable modification redux' >> a $ hg commit -m'a valuable change redux' $ rm .hg/undo.desc $ hg update 0 1 files updated, 0 files merged, 0 files removed, 0 files unresolved $ hg rollback rolling back unknown transaction $ cat a a corrupt journal test $ echo "foo" > .hg/store/journal $ hg recover rolling back interrupted transaction couldn't read journal entry 'foo\n'! checking changesets checking manifests crosschecking files in changesets and manifests checking files 1 files, 2 changesets, 2 total revisions rollback disabled by config $ cat >> $HGRCPATH <<EOF > [ui] > rollback = false > EOF $ echo narf >> pinky-sayings.txt $ hg add pinky-sayings.txt $ hg ci -m 'First one.' $ hg rollback abort: rollback is disabled because it is unsafe (see `hg help -v rollback` for information) [255]