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
Tests discovery against servers without getbundle support:
$ cat >> $HGRCPATH <<EOF
> [ui]
> logtemplate="{rev} {node|short}: {desc} {branches}\n"
> EOF
$ cp $HGRCPATH $HGRCPATH-withcap
$ CAP="getbundle known changegroupsubset bundle2"
$ . "$TESTDIR/notcapable"
$ cp $HGRCPATH $HGRCPATH-nocap
$ cp $HGRCPATH-withcap $HGRCPATH
Prep for test server without branchmap support
$ CAP="branchmap"
$ . "$TESTDIR/notcapable"
$ cp $HGRCPATH $HGRCPATH-nocap-branchmap
$ cp $HGRCPATH-withcap $HGRCPATH
Setup HTTP server control:
$ remote=http://localhost:$HGPORT/
$ export remote
$ tstart() {
> echo '[web]' > $1/.hg/hgrc
> echo 'push_ssl = false' >> $1/.hg/hgrc
> echo 'allow_push = *' >> $1/.hg/hgrc
> cp $HGRCPATH-nocap $HGRCPATH
> hg serve -R $1 -p $HGPORT -d --pid-file=hg.pid -E errors.log
> cat hg.pid >> $DAEMON_PIDS
> }
$ tstop() {
> killdaemons.py
> cp $HGRCPATH-withcap $HGRCPATH
> }
Both are empty:
$ hg init empty1
$ hg init empty2
$ tstart empty2
$ hg incoming -R empty1 $remote
comparing with http://localhost:$HGPORT/
no changes found
[1]
$ hg outgoing -R empty1 $remote
comparing with http://localhost:$HGPORT/
no changes found
[1]
$ hg pull -R empty1 $remote
pulling from http://localhost:$HGPORT/
no changes found
$ hg push -R empty1 $remote
pushing to http://localhost:$HGPORT/
no changes found
[1]
$ tstop
Base repo:
$ hg init main
$ cd main
$ hg debugbuilddag -mo '+2:tbase @name1 +3:thead1 <tbase @name2 +4:thead2 @both /thead1 +2:tmaintip'
$ hg log -G
o 11 a19bfa7e7328: r11 both
|
o 10 8b6bad1512e1: r10 both
|
o 9 025829e08038: r9 both
|\
| o 8 d8f638ac69e9: r8 name2
| |
| o 7 b6b4d315a2ac: r7 name2
| |
| o 6 6c6f5d5f3c11: r6 name2
| |
| o 5 70314b29987d: r5 name2
| |
o | 4 e71dbbc70e03: r4 name1
| |
o | 3 2c8d5d5ec612: r3 name1
| |
o | 2 a7892891da29: r2 name1
|/
o 1 0019a3b924fd: r1
|
o 0 d57206cc072a: r0
$ cd ..
$ tstart main
Full clone:
$ hg clone main full
updating to branch default
2 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ cd full
$ hg incoming $remote
comparing with http://localhost:$HGPORT/
searching for changes
no changes found
[1]
$ hg outgoing $remote
comparing with http://localhost:$HGPORT/
searching for changes
no changes found
[1]
$ hg pull $remote
pulling from http://localhost:$HGPORT/
searching for changes
no changes found
$ hg push $remote
pushing to http://localhost:$HGPORT/
searching for changes
no changes found
[1]
$ cd ..
Local is empty:
$ cd empty1
$ hg incoming $remote --rev name1
comparing with http://localhost:$HGPORT/
abort: cannot look up remote changes; remote repository does not support the 'changegroupsubset' capability!
[255]
$ hg incoming $remote
comparing with http://localhost:$HGPORT/
0 d57206cc072a: r0
1 0019a3b924fd: r1
2 a7892891da29: r2 name1
3 2c8d5d5ec612: r3 name1
4 e71dbbc70e03: r4 name1
5 70314b29987d: r5 name2
6 6c6f5d5f3c11: r6 name2
7 b6b4d315a2ac: r7 name2
8 d8f638ac69e9: r8 name2
9 025829e08038: r9 both
10 8b6bad1512e1: r10 both
11 a19bfa7e7328: r11 both
$ hg outgoing $remote
comparing with http://localhost:$HGPORT/
no changes found
[1]
$ hg push $remote
pushing to http://localhost:$HGPORT/
no changes found
[1]
$ hg pull $remote
pulling from http://localhost:$HGPORT/
requesting all changes
adding changesets
adding manifests
adding file changes
added 12 changesets with 24 changes to 2 files
(run 'hg update' to get a working copy)
$ hg incoming $remote
comparing with http://localhost:$HGPORT/
searching for changes
no changes found
[1]
$ cd ..
Local is subset:
$ cp $HGRCPATH-withcap $HGRCPATH
$ hg clone main subset --rev name2 ; cd subset
adding changesets
adding manifests
adding file changes
added 6 changesets with 12 changes to 2 files
updating to branch name2
2 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ cp $HGRCPATH-nocap $HGRCPATH
$ hg incoming $remote
comparing with http://localhost:$HGPORT/
searching for changes
6 a7892891da29: r2 name1
7 2c8d5d5ec612: r3 name1
8 e71dbbc70e03: r4 name1
9 025829e08038: r9 both
10 8b6bad1512e1: r10 both
11 a19bfa7e7328: r11 both
$ hg outgoing $remote
comparing with http://localhost:$HGPORT/
searching for changes
no changes found
[1]
$ hg push $remote
pushing to http://localhost:$HGPORT/
searching for changes
no changes found
[1]
$ hg pull $remote
pulling from http://localhost:$HGPORT/
searching for changes
adding changesets
adding manifests
adding file changes
added 6 changesets with 12 changes to 2 files
(run 'hg update' to get a working copy)
$ hg incoming $remote
comparing with http://localhost:$HGPORT/
searching for changes
no changes found
[1]
$ cd ..
Remote is empty:
$ tstop ; tstart empty2
$ cd main
$ hg incoming $remote
comparing with http://localhost:$HGPORT/
searching for changes
no changes found
[1]
$ hg outgoing $remote
comparing with http://localhost:$HGPORT/
searching for changes
0 d57206cc072a: r0
1 0019a3b924fd: r1
2 a7892891da29: r2 name1
3 2c8d5d5ec612: r3 name1
4 e71dbbc70e03: r4 name1
5 70314b29987d: r5 name2
6 6c6f5d5f3c11: r6 name2
7 b6b4d315a2ac: r7 name2
8 d8f638ac69e9: r8 name2
9 025829e08038: r9 both
10 8b6bad1512e1: r10 both
11 a19bfa7e7328: r11 both
$ hg pull $remote
pulling from http://localhost:$HGPORT/
searching for changes
no changes found
$ hg push $remote
pushing to http://localhost:$HGPORT/
searching for changes
remote: adding changesets
remote: adding manifests
remote: adding file changes
remote: added 12 changesets with 24 changes to 2 files
$ hg outgoing $remote
comparing with http://localhost:$HGPORT/
searching for changes
no changes found
[1]
$ cd ..
Local is superset:
$ tstop
$ hg clone main subset2 --rev name2
adding changesets
adding manifests
adding file changes
added 6 changesets with 12 changes to 2 files
updating to branch name2
2 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ tstart subset2
$ cd main
$ hg incoming $remote
comparing with http://localhost:$HGPORT/
searching for changes
no changes found
[1]
$ hg outgoing $remote
comparing with http://localhost:$HGPORT/
searching for changes
2 a7892891da29: r2 name1
3 2c8d5d5ec612: r3 name1
4 e71dbbc70e03: r4 name1
9 025829e08038: r9 both
10 8b6bad1512e1: r10 both
11 a19bfa7e7328: r11 both
$ hg pull $remote
pulling from http://localhost:$HGPORT/
searching for changes
no changes found
$ hg push $remote
pushing to http://localhost:$HGPORT/
searching for changes
abort: push creates new remote branches: both, name1!
(use 'hg push --new-branch' to create new remote branches)
[255]
$ hg push $remote --new-branch
pushing to http://localhost:$HGPORT/
searching for changes
remote: adding changesets
remote: adding manifests
remote: adding file changes
remote: added 6 changesets with 12 changes to 2 files
$ hg outgoing $remote
comparing with http://localhost:$HGPORT/
searching for changes
no changes found
[1]
$ cd ..
Partial pull:
$ tstop ; tstart main
$ hg clone $remote partial --rev name2
abort: partial pull cannot be done because other repository doesn't support changegroupsubset.
[255]
$ hg init partial; cd partial
$ hg incoming $remote --rev name2
comparing with http://localhost:$HGPORT/
abort: cannot look up remote changes; remote repository does not support the 'changegroupsubset' capability!
[255]
$ hg pull $remote --rev name2
pulling from http://localhost:$HGPORT/
abort: partial pull cannot be done because other repository doesn't support changegroupsubset.
[255]
$ cd ..
$ tstop
Exercise pushing to server without branchmap capability
$ cp $HGRCPATH-nocap-branchmap $HGRCPATH-nocap
$ hg init rlocal
$ cd rlocal
$ echo A > A
$ hg ci -Am A
adding A
$ cd ..
$ hg clone rlocal rremote
updating to branch default
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ cd rlocal
$ echo B > B
$ hg ci -Am B
adding B
$ cd ..
$ tstart rremote
$ cd rlocal
$ hg incoming $remote
comparing with http://localhost:$HGPORT/
searching for changes
no changes found
[1]
$ hg outgoing $remote
comparing with http://localhost:$HGPORT/
searching for changes
1 27547f69f254: B
$ hg pull $remote
pulling from http://localhost:$HGPORT/
searching for changes
no changes found
$ hg push $remote
pushing to http://localhost:$HGPORT/
searching for changes
remote: adding changesets
remote: adding manifests
remote: adding file changes
remote: added 1 changesets with 1 changes to 1 files
$ hg outgoing $remote
comparing with http://localhost:$HGPORT/
searching for changes
no changes found
[1]
$ cd ..
$ tstop