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...
$ . "$TESTDIR/histedit-helpers.sh"
$ cat >> $HGRCPATH <<EOF
> [extensions]
> histedit=
> strip=
> EOF
$ initrepo ()
> {
> hg init r
> cd r
> for x in a b c d e f g; do
> echo $x > $x
> hg add $x
> hg ci -m $x
> done
> }
$ initrepo
log before edit
$ hg log --graph
@ changeset: 6:3c6a8ed2ebe8
| tag: tip
| user: test
| date: Thu Jan 01 00:00:00 1970 +0000
| summary: g
|
o changeset: 5:652413bf663e
| user: test
| date: Thu Jan 01 00:00:00 1970 +0000
| summary: f
|
o changeset: 4:e860deea161a
| user: test
| date: Thu Jan 01 00:00:00 1970 +0000
| summary: e
|
o changeset: 3:055a42cdd887
| user: test
| date: Thu Jan 01 00:00:00 1970 +0000
| summary: d
|
o changeset: 2:177f92b77385
| user: test
| date: Thu Jan 01 00:00:00 1970 +0000
| summary: c
|
o changeset: 1:d2ae7f538514
| user: test
| date: Thu Jan 01 00:00:00 1970 +0000
| summary: b
|
o changeset: 0:cb9a9f314b8b
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: a
dirty a file
$ echo a > g
$ hg histedit 177f92b77385 --commands - 2>&1 << EOF
> EOF
abort: uncommitted changes
[255]
$ echo g > g
edit the history
$ hg histedit 177f92b77385 --commands - 2>&1 << EOF| fixbundle
> pick 177f92b77385 c
> pick 055a42cdd887 d
> edit e860deea161a e
> pick 652413bf663e f
> pick 3c6a8ed2ebe8 g
> EOF
0 files updated, 0 files merged, 3 files removed, 0 files unresolved
Editing (e860deea161a), you may commit or record as needed now.
(hg histedit --continue to resume)
try to update and get an error
$ hg update tip
abort: histedit in progress
(use 'hg histedit --continue' or 'hg histedit --abort')
[255]
edit the plan via the editor
$ cat >> $TESTTMP/editplan.sh <<EOF
> cat > \$1 <<EOF2
> drop e860deea161a e
> drop 652413bf663e f
> drop 3c6a8ed2ebe8 g
> EOF2
> EOF
$ HGEDITOR="sh $TESTTMP/editplan.sh" hg histedit --edit-plan
$ cat .hg/histedit-state
v1
055a42cdd88768532f9cf79daa407fc8d138de9b
3c6a8ed2ebe862cc949d2caa30775dd6f16fb799
False
3
drop
e860deea161a2f77de56603b340ebbb4536308ae
drop
652413bf663ef2a641cab26574e46d5f5a64a55a
drop
3c6a8ed2ebe862cc949d2caa30775dd6f16fb799
0
strip-backup/177f92b77385-0ebe6a8f-histedit.hg
edit the plan via --commands
$ hg histedit --edit-plan --commands - 2>&1 << EOF
> edit e860deea161a e
> pick 652413bf663e f
> drop 3c6a8ed2ebe8 g
> EOF
$ cat .hg/histedit-state
v1
055a42cdd88768532f9cf79daa407fc8d138de9b
3c6a8ed2ebe862cc949d2caa30775dd6f16fb799
False
3
edit
e860deea161a2f77de56603b340ebbb4536308ae
pick
652413bf663ef2a641cab26574e46d5f5a64a55a
drop
3c6a8ed2ebe862cc949d2caa30775dd6f16fb799
0
strip-backup/177f92b77385-0ebe6a8f-histedit.hg
Go at a random point and try to continue
$ hg id -n
3+
$ hg up 0
abort: histedit in progress
(use 'hg histedit --continue' or 'hg histedit --abort')
[255]
Try to delete necessary commit
$ hg strip -r 652413b
abort: histedit in progress, can't strip 652413bf663e
[255]
commit, then edit the revision
$ hg ci -m 'wat'
created new head
$ echo a > e
qnew should fail while we're in the middle of the edit step
$ hg --config extensions.mq= qnew please-fail
abort: histedit in progress
(use 'hg histedit --continue' or 'hg histedit --abort')
[255]
$ HGEDITOR='echo foobaz > ' hg histedit --continue 2>&1 | fixbundle
$ hg log --graph
@ changeset: 6:b5f70786f9b0
| tag: tip
| user: test
| date: Thu Jan 01 00:00:00 1970 +0000
| summary: f
|
o changeset: 5:a5e1ba2f7afb
| user: test
| date: Thu Jan 01 00:00:00 1970 +0000
| summary: foobaz
|
o changeset: 4:1a60820cd1f6
| user: test
| date: Thu Jan 01 00:00:00 1970 +0000
| summary: wat
|
o changeset: 3:055a42cdd887
| user: test
| date: Thu Jan 01 00:00:00 1970 +0000
| summary: d
|
o changeset: 2:177f92b77385
| user: test
| date: Thu Jan 01 00:00:00 1970 +0000
| summary: c
|
o changeset: 1:d2ae7f538514
| user: test
| date: Thu Jan 01 00:00:00 1970 +0000
| summary: b
|
o changeset: 0:cb9a9f314b8b
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: a
$ hg cat e
a
Stripping necessary commits should not break --abort
$ hg histedit 1a60820cd1f6 --commands - 2>&1 << EOF| fixbundle
> edit 1a60820cd1f6 wat
> pick a5e1ba2f7afb foobaz
> pick b5f70786f9b0 g
> EOF
0 files updated, 0 files merged, 2 files removed, 0 files unresolved
Editing (1a60820cd1f6), you may commit or record as needed now.
(hg histedit --continue to resume)
$ mv .hg/histedit-state .hg/histedit-state.bak
$ hg strip -q -r b5f70786f9b0
$ mv .hg/histedit-state.bak .hg/histedit-state
$ hg histedit --abort
adding changesets
adding manifests
adding file changes
added 1 changesets with 1 changes to 3 files
2 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg log -r .
changeset: 6:b5f70786f9b0
tag: tip
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: f
check histedit_source
$ hg log --debug --rev 5
changeset: 5:a5e1ba2f7afb899ef1581cea528fd885d2fca70d
phase: draft
parent: 4:1a60820cd1f6004a362aa622ebc47d59bc48eb34
parent: -1:0000000000000000000000000000000000000000
manifest: 5:5ad3be8791f39117565557781f5464363b918a45
user: test
date: Thu Jan 01 00:00:00 1970 +0000
files: e
extra: branch=default
extra: histedit_source=e860deea161a2f77de56603b340ebbb4536308ae
description:
foobaz
$ hg histedit tip --commands - 2>&1 <<EOF| fixbundle
> edit b5f70786f9b0 f
> EOF
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
Editing (b5f70786f9b0), you may commit or record as needed now.
(hg histedit --continue to resume)
$ hg status
A f
$ hg summary
parent: 5:a5e1ba2f7afb
foobaz
branch: default
commit: 1 added (new branch head)
update: 1 new changesets (update)
phases: 7 draft
hist: 1 remaining (histedit --continue)
(test also that editor is invoked if histedit is continued for
"edit" action)
$ HGEDITOR='cat' hg histedit --continue
f
HG: Enter commit message. Lines beginning with 'HG:' are removed.
HG: Leave message empty to abort commit.
HG: --
HG: user: test
HG: branch 'default'
HG: added f
saved backup bundle to $TESTTMP/r/.hg/strip-backup/b5f70786f9b0-c28d9c86-backup.hg (glob)
$ hg status
log after edit
$ hg log --limit 1
changeset: 6:a107ee126658
tag: tip
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: f
say we'll change the message, but don't.
$ cat > ../edit.sh <<EOF
> cat "\$1" | sed s/pick/mess/ > tmp
> mv tmp "\$1"
> EOF
$ HGEDITOR="sh ../edit.sh" hg histedit tip 2>&1 | fixbundle
$ hg status
$ hg log --limit 1
changeset: 6:1fd3b2fe7754
tag: tip
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: f
modify the message
check saving last-message.txt, at first
$ cat > $TESTTMP/commitfailure.py <<EOF
> from mercurial import error
> def reposetup(ui, repo):
> class commitfailure(repo.__class__):
> def commit(self, *args, **kwargs):
> raise error.Abort('emulating unexpected abort')
> repo.__class__ = commitfailure
> EOF
$ cat >> .hg/hgrc <<EOF
> [extensions]
> # this failure occurs before editor invocation
> commitfailure = $TESTTMP/commitfailure.py
> EOF
$ cat > $TESTTMP/editor.sh <<EOF
> echo "==== before editing"
> cat \$1
> echo "===="
> echo "check saving last-message.txt" >> \$1
> EOF
(test that editor is not invoked before transaction starting)
$ rm -f .hg/last-message.txt
$ HGEDITOR="sh $TESTTMP/editor.sh" hg histedit tip --commands - 2>&1 << EOF | fixbundle
> mess 1fd3b2fe7754 f
> EOF
abort: emulating unexpected abort
$ test -f .hg/last-message.txt
[1]
$ cat >> .hg/hgrc <<EOF
> [extensions]
> commitfailure = !
> EOF
$ hg histedit --abort -q
(test that editor is invoked and commit message is saved into
"last-message.txt")
$ cat >> .hg/hgrc <<EOF
> [hooks]
> # this failure occurs after editor invocation
> pretxncommit.unexpectedabort = false
> EOF
$ hg status --rev '1fd3b2fe7754^1' --rev 1fd3b2fe7754
A f
$ rm -f .hg/last-message.txt
$ HGEDITOR="sh $TESTTMP/editor.sh" hg histedit tip --commands - 2>&1 << EOF
> mess 1fd3b2fe7754 f
> EOF
==== before editing
f
HG: Enter commit message. Lines beginning with 'HG:' are removed.
HG: Leave message empty to abort commit.
HG: --
HG: user: test
HG: branch 'default'
HG: added f
====
note: commit message saved in .hg/last-message.txt
transaction abort!
rollback completed
abort: pretxncommit.unexpectedabort hook exited with status 1
[255]
$ cat .hg/last-message.txt
f
check saving last-message.txt
(test also that editor is invoked if histedit is continued for "message"
action)
$ HGEDITOR=cat hg histedit --continue
f
HG: Enter commit message. Lines beginning with 'HG:' are removed.
HG: Leave message empty to abort commit.
HG: --
HG: user: test
HG: branch 'default'
HG: added f
note: commit message saved in .hg/last-message.txt
transaction abort!
rollback completed
abort: pretxncommit.unexpectedabort hook exited with status 1
[255]
$ cat >> .hg/hgrc <<EOF
> [hooks]
> pretxncommit.unexpectedabort =
> EOF
$ hg histedit --abort -q
then, check "modify the message" itself
$ hg histedit tip --commands - 2>&1 << EOF | fixbundle
> mess 1fd3b2fe7754 f
> EOF
$ hg status
$ hg log --limit 1
changeset: 6:62feedb1200e
tag: tip
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: f
rollback should not work after a histedit
$ hg rollback
no rollback information available
[1]
$ cd ..
$ hg clone -qr0 r r0
$ cd r0
$ hg phase -fdr0
$ hg histedit --commands - 0 2>&1 << EOF
> edit cb9a9f314b8b a > $EDITED
> EOF
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
adding a
Editing (cb9a9f314b8b), you may commit or record as needed now.
(hg histedit --continue to resume)
[1]
$ HGEDITOR=true hg histedit --continue
saved backup bundle to $TESTTMP/r0/.hg/strip-backup/cb9a9f314b8b-cc5ccb0b-backup.hg (glob)
$ hg log -G
@ changeset: 0:0efcea34f18a
tag: tip
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: a
$ echo foo >> b
$ hg addr
adding b
$ hg ci -m 'add b'
$ echo foo >> a
$ hg ci -m 'extend a'
$ hg phase --public 1
Attempting to fold a change into a public change should not work:
$ cat > ../edit.sh <<EOF
> cat "\$1" | sed s/pick/fold/ > tmp
> mv tmp "\$1"
> EOF
$ HGEDITOR="sh ../edit.sh" hg histedit 2
warning: histedit rules saved to: .hg/histedit-last-edit.txt
hg: parse error: cannot fold into public change 18aa70c8ad22
[255]
$ cat .hg/histedit-last-edit.txt
fold 0012be4a27ea 2 extend a
# Edit history between 0012be4a27ea and 0012be4a27ea
#
# Commits are listed from least to most recent
#
# You can reorder changesets by reordering the lines
#
# Commands:
#
# e, edit = use commit, but stop for amending
# m, mess = edit commit message without changing commit content
# p, fold = use commit
# d, drop = remove commit from history
# f, fold = use commit, but combine it with the one above
# r, roll = like fold, but discard this commit's description
#