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localrepo: experimental support for non-zlib revlog compression...
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...

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mergetools.rc
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# Some default global settings for common merge tools
[merge-tools]
kdiff3.args=--auto --L1 base --L2 local --L3 other $base $local $other -o $output
kdiff3.regkey=Software\KDiff3
kdiff3.regkeyalt=Software\Wow6432Node\KDiff3
kdiff3.regappend=\kdiff3.exe
kdiff3.fixeol=True
kdiff3.gui=True
kdiff3.diffargs=--L1 $plabel1 --L2 $clabel $parent $child
gvimdiff.args=--nofork -d -g -O $local $other $base
gvimdiff.regkey=Software\Vim\GVim
gvimdiff.regkeyalt=Software\Wow6432Node\Vim\GVim
gvimdiff.regname=path
gvimdiff.priority=-9
gvimdiff.diffargs=--nofork -d -g -O $parent $child
vimdiff.args=$local $other $base -c 'redraw | echomsg "hg merge conflict, type \":cq\" to abort vimdiff"'
vimdiff.check=changed
vimdiff.priority=-10
merge.check=conflicts
merge.priority=-100
gpyfm.gui=True
meld.gui=True
meld.args=--label='local' $local --label='merged' $base --label='other' $other -o $output
meld.check=changed
meld.diffargs=-a --label=$plabel1 $parent --label=$clabel $child
tkdiff.args=$local $other -a $base -o $output
tkdiff.gui=True
tkdiff.priority=-8
tkdiff.diffargs=-L $plabel1 $parent -L $clabel $child
xxdiff.args=--show-merged-pane --exit-with-merge-status --title1 local --title2 base --title3 other --merged-filename $output --merge $local $base $other
xxdiff.gui=True
xxdiff.priority=-8
xxdiff.diffargs=--title1 $plabel1 $parent --title2 $clabel $child
diffmerge.regkey=Software\SourceGear\SourceGear DiffMerge\
diffmerge.regkeyalt=Software\Wow6432Node\SourceGear\SourceGear DiffMerge\
diffmerge.regname=Location
diffmerge.priority=-7
diffmerge.args=-nosplash -merge -title1=local -title2=merged -title3=other $local $base $other -result=$output
diffmerge.check=changed
diffmerge.gui=True
diffmerge.diffargs=--nosplash --title1=$plabel1 --title2=$clabel $parent $child
p4merge.args=$base $local $other $output
p4merge.regkey=Software\Perforce\Environment
p4merge.regkeyalt=Software\Wow6432Node\Perforce\Environment
p4merge.regname=P4INSTROOT
p4merge.regappend=\p4merge.exe
p4merge.gui=True
p4merge.priority=-8
p4merge.diffargs=$parent $child
p4mergeosx.executable = /Applications/p4merge.app/Contents/MacOS/p4merge
p4mergeosx.args = $base $local $other $output
p4mergeosx.gui = True
p4mergeosx.priority=-8
p4mergeosx.diffargs=$parent $child
tortoisemerge.args=/base:$base /mine:$local /theirs:$other /merged:$output
tortoisemerge.regkey=Software\TortoiseSVN
tortoisemerge.regkeyalt=Software\Wow6432Node\TortoiseSVN
tortoisemerge.check=changed
tortoisemerge.gui=True
tortoisemerge.priority=-8
tortoisemerge.diffargs=/base:$parent /mine:$child /basename:$plabel1 /minename:$clabel
ecmerge.args=$base $local $other --mode=merge3 --title0=base --title1=local --title2=other --to=$output
ecmerge.regkey=Software\Elli\xc3\xa9 Computing\Merge
ecmerge.regkeyalt=Software\Wow6432Node\Elli\xc3\xa9 Computing\Merge
ecmerge.gui=True
ecmerge.diffargs=$parent $child --mode=diff2 --title1=$plabel1 --title2=$clabel
# editmerge is a small script shipped in contrib.
# It needs this config otherwise it behaves the same as internal:local
editmerge.args=$output
editmerge.check=changed
editmerge.premerge=keep
filemerge.executable=/Developer/Applications/Utilities/FileMerge.app/Contents/MacOS/FileMerge
filemerge.args=-left $other -right $local -ancestor $base -merge $output
filemerge.gui=True
filemergexcode.executable=/Applications/Xcode.app/Contents/Applications/FileMerge.app/Contents/MacOS/FileMerge
filemergexcode.args=-left $other -right $local -ancestor $base -merge $output
filemergexcode.gui=True
; Windows version of Beyond Compare
beyondcompare3.args=$local $other $base $output /ro /lefttitle=local /centertitle=base /righttitle=other /automerge /reviewconflicts /solo
beyondcompare3.regkey=Software\Scooter Software\Beyond Compare 3
beyondcompare3.regname=ExePath
beyondcompare3.gui=True
beyondcompare3.priority=-2
beyondcompare3.diffargs=/lro /lefttitle=$plabel1 /righttitle=$clabel /solo /expandall $parent $child
; Linux version of Beyond Compare
bcompare.args=$local $other $base -mergeoutput=$output -ro -lefttitle=parent1 -centertitle=base -righttitle=parent2 -outputtitle=merged -automerge -reviewconflicts -solo
bcompare.gui=True
bcompare.priority=-1
bcompare.diffargs=-lro -lefttitle=$plabel1 -righttitle=$clabel -solo -expandall $parent $child
; OS X version of Beyond Compare
bcomposx.executable = /Applications/Beyond Compare.app/Contents/MacOS/bcomp
bcomposx.args=$local $other $base -mergeoutput=$output -ro -lefttitle=parent1 -centertitle=base -righttitle=parent2 -outputtitle=merged -automerge -reviewconflicts -solo
bcomposx.gui=True
bcomposx.priority=-1
bcomposx.diffargs=-lro -lefttitle=$plabel1 -righttitle=$clabel -solo -expandall $parent $child
winmerge.args=/e /x /wl /ub /dl other /dr local $other $local $output
winmerge.regkey=Software\Thingamahoochie\WinMerge
winmerge.regkeyalt=Software\Wow6432Node\Thingamahoochie\WinMerge\
winmerge.regname=Executable
winmerge.check=changed
winmerge.gui=True
winmerge.priority=-10
winmerge.diffargs=/r /e /x /ub /wl /dl $plabel1 /dr $clabel $parent $child
araxis.regkey=SOFTWARE\Classes\TypeLib\{46799e0a-7bd1-4330-911c-9660bb964ea2}\7.0\HELPDIR
araxis.regappend=\ConsoleCompare.exe
araxis.priority=-2
araxis.args=/3 /a2 /wait /merge /title1:"Other" /title2:"Base" /title3:"Local :"$local $other $base $local $output
araxis.checkconflict=True
araxis.binary=True
araxis.gui=True
araxis.diffargs=/2 /wait /title1:$plabel1 /title2:$clabel $parent $child
diffuse.priority=-3
diffuse.args=$local $base $other
diffuse.gui=True
diffuse.diffargs=$parent $child
UltraCompare.regkey=Software\Microsoft\Windows\CurrentVersion\App Paths\UC.exe
UltraCompare.regkeyalt=Software\Wow6432Node\Microsoft\Windows\CurrentVersion\App Paths\UC.exe
UltraCompare.args = $base $local $other -title1 base -title3 other
UltraCompare.priority = -2
UltraCompare.gui = True
UltraCompare.binary = True
UltraCompare.check = conflicts,changed
UltraCompare.diffargs=$child $parent -title1 $clabel -title2 $plabel1