localrepo: experimental support for non-zlib revlog compression
The final part of integrating the compression manager APIs into
revlog storage is the plumbing for repositories to advertise they
are using non-zlib storage and for revlogs to instantiate a non-zlib
compression engine.
The main intent of the compression manager work was to zstd all
of the things. Adding zstd to revlogs has proved to be more involved
than other places because revlogs are... special. Very small inputs
and the use of delta chains (which are themselves a form of
compression) are a completely different use case from streaming
compression, which bundles and the wire protocol employ. I've
conducted numerous experiments with zstd in revlogs and have yet
to formalize compression settings and a storage architecture that
I'm confident I won't regret later. In other words, I'm not yet
ready to commit to a new mechanism for using zstd - or any other
compression format - in revlogs.
That being said, having some support for zstd (and other compression
formats) in revlogs in core is beneficial. It can allow others to
conduct experiments.
This patch introduces *highly experimental* support for non-zlib
compression formats in revlogs. Introduced is a config option to
control which compression engine to use. Also introduced is a namespace
of "exp-compression-*" requirements to denote support for non-zlib
compression in revlogs. I've prefixed the namespace with "exp-"
(short for "experimental") because I'm not confident of the
requirements "schema" and in no way want to give the illusion of
supporting these requirements in the future. I fully intend to drop
support for these requirements once we figure out what we're doing
with zstd in revlogs.
A good portion of the patch is teaching the requirements system
about registered compression engines and passing the requested
compression engine as an opener option so revlogs can instantiate
the proper compression engine for new operations.
That's a verbose way of saying "we can now use zstd in revlogs!"
On an `hg pull` conversion of the mozilla-unified repo with no extra
redelta settings (like aggressivemergedeltas), we can see the impact
of zstd vs zlib in revlogs:
$ hg perfrevlogchunks -c
! chunk
! wall 2.032052 comb 2.040000 user 1.990000 sys 0.050000 (best of 5)
! wall 1.866360 comb 1.860000 user 1.820000 sys 0.040000 (best of 6)
! chunk batch
! wall 1.877261 comb 1.870000 user 1.860000 sys 0.010000 (best of 6)
! wall 1.705410 comb 1.710000 user 1.690000 sys 0.020000 (best of 6)
$ hg perfrevlogchunks -m
! chunk
! wall 2.721427 comb 2.720000 user 2.640000 sys 0.080000 (best of 4)
! wall 2.035076 comb 2.030000 user 1.950000 sys 0.080000 (best of 5)
! chunk batch
! wall 2.614561 comb 2.620000 user 2.580000 sys 0.040000 (best of 4)
! wall 1.910252 comb 1.910000 user 1.880000 sys 0.030000 (best of 6)
$ hg perfrevlog -c -d 1
! wall 4.812885 comb 4.820000 user 4.800000 sys 0.020000 (best of 3)
! wall 4.699621 comb 4.710000 user 4.700000 sys 0.010000 (best of 3)
$ hg perfrevlog -m -d 1000
! wall 34.252800 comb 34.250000 user 33.730000 sys 0.520000 (best of 3)
! wall 24.094999 comb 24.090000 user 23.320000 sys 0.770000 (best of 3)
Only modest wins for the changelog. But manifest reading is
significantly faster. What's going on?
One reason might be data volume. zstd decompresses faster. So given
more bytes, it will put more distance between it and zlib.
Another reason is size. In the current design, zstd revlogs are
*larger*:
debugcreatestreamclonebundle (size in bytes)
zlib: 1,638,852,492
zstd: 1,680,601,332
I haven't investigated this fully, but I reckon a significant cause of
larger revlogs is that the zstd frame/header has more bytes than
zlib's. For very small inputs or data that doesn't compress well, we'll
tend to store more uncompressed chunks than with zlib (because the
compressed size isn't smaller than original). This will make revlog
reading faster because it is doing less decompression.
Moving on to bundle performance:
$ hg bundle -a -t none-v2 (total CPU time)
zlib: 102.79s
zstd: 97.75s
So, marginal CPU decrease for reading all chunks in all revlogs
(this is somewhat disappointing).
$ hg bundle -a -t <engine>-v2 (total CPU time)
zlib: 191.59s
zstd: 115.36s
This last test effectively measures the difference between zlib->zlib
and zstd->zstd for revlogs to bundle. This is a rough approximation of
what a server does during `hg clone`.
There are some promising results for zstd. But not enough for me to
feel comfortable advertising it to users. We'll get there...
#require killdaemons
$ echo "[extensions]" >> $HGRCPATH
$ echo "share = " >> $HGRCPATH
prepare repo1
$ hg init repo1
$ cd repo1
$ echo a > a
$ hg commit -A -m'init'
adding a
share it
$ cd ..
$ hg share repo1 repo2
updating working directory
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
share shouldn't have a store dir
$ cd repo2
$ test -d .hg/store
[1]
Some sed versions appends newline, some don't, and some just fails
$ cat .hg/sharedpath; echo
$TESTTMP/repo1/.hg (glob)
trailing newline on .hg/sharedpath is ok
$ hg tip -q
0:d3873e73d99e
$ echo '' >> .hg/sharedpath
$ cat .hg/sharedpath
$TESTTMP/repo1/.hg (glob)
$ hg tip -q
0:d3873e73d99e
commit in shared clone
$ echo a >> a
$ hg commit -m'change in shared clone'
check original
$ cd ../repo1
$ hg log
changeset: 1:8af4dc49db9e
tag: tip
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: change in shared clone
changeset: 0:d3873e73d99e
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: init
$ hg update
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ cat a # should be two lines of "a"
a
a
commit in original
$ echo b > b
$ hg commit -A -m'another file'
adding b
check in shared clone
$ cd ../repo2
$ hg log
changeset: 2:c2e0ac586386
tag: tip
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: another file
changeset: 1:8af4dc49db9e
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: change in shared clone
changeset: 0:d3873e73d99e
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: init
$ hg update
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ cat b # should exist with one "b"
b
hg serve shared clone
$ hg serve -n test -p $HGPORT -d --pid-file=hg.pid
$ cat hg.pid >> $DAEMON_PIDS
$ get-with-headers.py localhost:$HGPORT 'raw-file/'
200 Script output follows
-rw-r--r-- 4 a
-rw-r--r-- 2 b
test unshare command
$ hg unshare
$ test -d .hg/store
$ test -f .hg/sharedpath
[1]
$ hg unshare
abort: this is not a shared repo
[255]
check that a change does not propagate
$ echo b >> b
$ hg commit -m'change in unshared'
$ cd ../repo1
$ hg id -r tip
c2e0ac586386 tip
$ cd ..
test sharing bookmarks
$ hg share -B repo1 repo3
updating working directory
2 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ cd repo1
$ hg bookmark bm1
$ hg bookmarks
* bm1 2:c2e0ac586386
$ cd ../repo2
$ hg book bm2
$ hg bookmarks
* bm2 3:0e6e70d1d5f1
$ cd ../repo3
$ hg bookmarks
bm1 2:c2e0ac586386
$ hg book bm3
$ hg bookmarks
bm1 2:c2e0ac586386
* bm3 2:c2e0ac586386
$ cd ../repo1
$ hg bookmarks
* bm1 2:c2e0ac586386
bm3 2:c2e0ac586386
test that commits work
$ echo 'shared bookmarks' > a
$ hg commit -m 'testing shared bookmarks'
$ hg bookmarks
* bm1 3:b87954705719
bm3 2:c2e0ac586386
$ cd ../repo3
$ hg bookmarks
bm1 3:b87954705719
* bm3 2:c2e0ac586386
$ echo 'more shared bookmarks' > a
$ hg commit -m 'testing shared bookmarks'
created new head
$ hg bookmarks
bm1 3:b87954705719
* bm3 4:62f4ded848e4
$ cd ../repo1
$ hg bookmarks
* bm1 3:b87954705719
bm3 4:62f4ded848e4
$ cd ..
test pushing bookmarks works
$ hg clone repo3 repo4
updating to branch default
2 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ cd repo4
$ hg boo bm4
$ echo foo > b
$ hg commit -m 'foo in b'
$ hg boo
bm1 3:b87954705719
bm3 4:62f4ded848e4
* bm4 5:92793bfc8cad
$ hg push -B bm4
pushing to $TESTTMP/repo3 (glob)
searching for changes
adding changesets
adding manifests
adding file changes
added 1 changesets with 1 changes to 1 files
exporting bookmark bm4
$ cd ../repo1
$ hg bookmarks
* bm1 3:b87954705719
bm3 4:62f4ded848e4
bm4 5:92793bfc8cad
$ cd ../repo3
$ hg bookmarks
bm1 3:b87954705719
* bm3 4:62f4ded848e4
bm4 5:92793bfc8cad
$ cd ..
test behavior when sharing a shared repo
$ hg share -B repo3 repo5
updating working directory
2 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ cd repo5
$ hg book
bm1 3:b87954705719
bm3 4:62f4ded848e4
bm4 5:92793bfc8cad
$ cd ..
test what happens when an active bookmark is deleted
$ cd repo1
$ hg boo -d bm3
$ hg boo
* bm1 3:b87954705719
bm4 5:92793bfc8cad
$ cd ../repo3
$ hg boo
bm1 3:b87954705719
bm4 5:92793bfc8cad
$ cd ..
verify that bookmarks are not written on failed transaction
$ cat > failpullbookmarks.py << EOF
> """A small extension that makes bookmark pulls fail, for testing"""
> from mercurial import extensions, exchange, error
> def _pullbookmarks(orig, pullop):
> orig(pullop)
> raise error.HookAbort('forced failure by extension')
> def extsetup(ui):
> extensions.wrapfunction(exchange, '_pullbookmarks', _pullbookmarks)
> EOF
$ cd repo4
$ hg boo
bm1 3:b87954705719
bm3 4:62f4ded848e4
* bm4 5:92793bfc8cad
$ cd ../repo3
$ hg boo
bm1 3:b87954705719
bm4 5:92793bfc8cad
$ hg --config "extensions.failpullbookmarks=$TESTTMP/failpullbookmarks.py" pull $TESTTMP/repo4
pulling from $TESTTMP/repo4 (glob)
searching for changes
no changes found
adding remote bookmark bm3
abort: forced failure by extension
[255]
$ hg boo
bm1 3:b87954705719
bm4 5:92793bfc8cad
$ hg pull $TESTTMP/repo4
pulling from $TESTTMP/repo4 (glob)
searching for changes
no changes found
adding remote bookmark bm3
$ hg boo
bm1 3:b87954705719
* bm3 4:62f4ded848e4
bm4 5:92793bfc8cad
$ cd ..
verify bookmark behavior after unshare
$ cd repo3
$ hg unshare
$ hg boo
bm1 3:b87954705719
* bm3 4:62f4ded848e4
bm4 5:92793bfc8cad
$ hg boo -d bm4
$ hg boo bm5
$ hg boo
bm1 3:b87954705719
bm3 4:62f4ded848e4
* bm5 4:62f4ded848e4
$ cd ../repo1
$ hg boo
* bm1 3:b87954705719
bm3 4:62f4ded848e4
bm4 5:92793bfc8cad
$ cd ..
Explicitly kill daemons to let the test exit on Windows
$ killdaemons.py