view tests/test-convert-filemap.t @ 24735:07200e3332a1

tags: extract .hgtags filenodes cache to a standalone file

Resolution of .hgtags filenodes values has historically been a
performance pain point for large repositories, where reading individual
manifests can take over 100ms. Multiplied by hundreds or even thousands
of heads and resolving .hgtags filenodes becomes a performance issue.

This patch establishes a standalone cache file holding the .hgtags
filenodes for each changeset. After this patch, the .hgtags filenode
for any particular changeset should only have to be computed once
during the lifetime of the repository.

The introduced hgtagsfnodes1 cache file is modeled after the rev branch
cache: the cache is effectively an array of entries consisting of a
changeset fragment and the filenode for a revision. The file grows in
proportion to the length of the repository (24 bytes per changeset) and
is truncated when the repository is stripped. The file is not written
unless tag info is requested and tags have changed since last time.

This patch partially addresses issue4550. Future patches will split the
"tags" cache file into per-filter files and will refactor the cache
format to not capture the .hgtags fnodes, as these are now stored in
the hgtagsfnodes1 cache. This patch is capable of standing alone. We
should not have to wait on the tags cache filter split and format
refactor for this patch to land.

  $ HGMERGE=true; export HGMERGE
  $ echo '[extensions]' >> $HGRCPATH
  $ echo 'convert =' >> $HGRCPATH
  $ glog()
  > {
  >     hg log -G --template '{rev} "{desc}" files: {files}\n' "$@"
  > }
  $ hg init source
  $ cd source
  $ echo foo > foo
  $ echo baz > baz
  $ mkdir -p dir/subdir
  $ echo dir/file >> dir/file
  $ echo dir/file2 >> dir/file2
  $ echo dir/file3 >> dir/file3 # to be corrupted in rev 0
  $ echo dir/subdir/file3 >> dir/subdir/file3
  $ echo dir/subdir/file4 >> dir/subdir/file4
  $ hg ci -d '0 0' -qAm '0: add foo baz dir/'
  $ echo bar > bar
  $ echo quux > quux
  $ echo dir/file4 >> dir/file4 # to be corrupted in rev 1
  $ hg copy foo copied
  $ hg ci -d '1 0' -qAm '1: add bar quux; copy foo to copied'
  $ echo >> foo
  $ hg ci -d '2 0' -m '2: change foo'
  $ hg up -qC 1
  $ echo >> bar
  $ echo >> quux
  $ hg ci -d '3 0' -m '3: change bar quux'
  created new head
  $ hg up -qC 2
  $ hg merge -qr 3
  $ echo >> bar
  $ echo >> baz
  $ hg ci -d '4 0' -m '4: first merge; change bar baz'
  $ echo >> bar
  $ echo 1 >> baz
  $ echo >> quux
  $ hg ci -d '5 0' -m '5: change bar baz quux'
  $ hg up -qC 4
  $ echo >> foo
  $ echo 2 >> baz
  $ hg ci -d '6 0' -m '6: change foo baz'
  created new head
  $ hg up -qC 5
  $ hg merge -qr 6
  $ echo >> bar
  $ hg ci -d '7 0' -m '7: second merge; change bar'
  $ echo >> foo
  $ hg ci -m '8: change foo'
  $ glog
  @  8 "8: change foo" files: foo
  |
  o    7 "7: second merge; change bar" files: bar baz
  |\
  | o  6 "6: change foo baz" files: baz foo
  | |
  o |  5 "5: change bar baz quux" files: bar baz quux
  |/
  o    4 "4: first merge; change bar baz" files: bar baz
  |\
  | o  3 "3: change bar quux" files: bar quux
  | |
  o |  2 "2: change foo" files: foo
  |/
  o  1 "1: add bar quux; copy foo to copied" files: bar copied dir/file4 quux
  |
  o  0 "0: add foo baz dir/" files: baz dir/file dir/file2 dir/file3 dir/subdir/file3 dir/subdir/file4 foo
  

final file versions in this repo:

  $ hg manifest --debug
  9463f52fe115e377cf2878d4fc548117211063f2 644   bar
  94c1be4dfde2ee8d78db8bbfcf81210813307c3d 644   baz
  7711d36246cc83e61fb29cd6d4ef394c63f1ceaf 644   copied
  3e20847584beff41d7cd16136b7331ab3d754be0 644   dir/file
  75e6d3f8328f5f6ace6bf10b98df793416a09dca 644   dir/file2
  e96dce0bc6a217656a3a410e5e6bec2c4f42bf7c 644   dir/file3
  6edd55f559cdce67132b12ca09e09cee08b60442 644   dir/file4
  5fe139720576e18e34bcc9f79174db8897c8afe9 644   dir/subdir/file3
  57a1c1511590f3de52874adfa04effe8a77d64af 644   dir/subdir/file4
  9a7b52012991e4873687192c3e17e61ba3e837a3 644   foo
  bc3eca3f47023a3e70ca0d8cc95a22a6827db19d 644   quux
  $ hg debugrename copied
  copied renamed from foo:2ed2a3912a0b24502043eae84ee4b279c18b90dd

  $ cd ..


Test interaction with startrev and verify that changing it is handled properly:

  $ > empty
  $ hg convert --filemap empty source movingstart --config convert.hg.startrev=3 -r4
  initializing destination movingstart repository
  scanning source...
  sorting...
  converting...
  1 3: change bar quux
  0 4: first merge; change bar baz
  $ hg convert --filemap empty source movingstart
  scanning source...
  sorting...
  converting...
  3 5: change bar baz quux
  2 6: change foo baz
  1 7: second merge; change bar
  warning: af455ce4166b3c9c88e6309c2b9332171dcea595 parent 61e22ca76c3b3e93df20338c4e02ce286898e825 is missing
  warning: cf908b3eeedc301c9272ebae931da966d5b326c7 parent 59e1ab45c888289513b7354484dac8a88217beab is missing
  0 8: change foo


splitrepo tests

  $ splitrepo()
  > {
  >     msg="$1"
  >     files="$2"
  >     opts=$3
  >     echo "% $files: $msg"
  >     prefix=`echo "$files" | sed -e 's/ /-/g'`
  >     fmap="$prefix.fmap"
  >     repo="$prefix.repo"
  >     for i in $files; do
  >         echo "include $i" >> "$fmap"
  >     done
  >     hg -q convert $opts --filemap "$fmap" --datesort source "$repo"
  >     hg up -q -R "$repo"
  >     glog -R "$repo"
  >     hg -R "$repo" manifest --debug
  > }
  $ splitrepo 'skip unwanted merges; use 1st parent in 1st merge, 2nd in 2nd' foo
  % foo: skip unwanted merges; use 1st parent in 1st merge, 2nd in 2nd
  @  3 "8: change foo" files: foo
  |
  o  2 "6: change foo baz" files: foo
  |
  o  1 "2: change foo" files: foo
  |
  o  0 "0: add foo baz dir/" files: foo
  
  9a7b52012991e4873687192c3e17e61ba3e837a3 644   foo
  $ splitrepo 'merges are not merges anymore' bar
  % bar: merges are not merges anymore
  @  4 "7: second merge; change bar" files: bar
  |
  o  3 "5: change bar baz quux" files: bar
  |
  o  2 "4: first merge; change bar baz" files: bar
  |
  o  1 "3: change bar quux" files: bar
  |
  o  0 "1: add bar quux; copy foo to copied" files: bar
  
  9463f52fe115e377cf2878d4fc548117211063f2 644   bar
  $ splitrepo '1st merge is not a merge anymore; 2nd still is' baz
  % baz: 1st merge is not a merge anymore; 2nd still is
  @    4 "7: second merge; change bar" files: baz
  |\
  | o  3 "6: change foo baz" files: baz
  | |
  o |  2 "5: change bar baz quux" files: baz
  |/
  o  1 "4: first merge; change bar baz" files: baz
  |
  o  0 "0: add foo baz dir/" files: baz
  
  94c1be4dfde2ee8d78db8bbfcf81210813307c3d 644   baz
  $ splitrepo 'we add additional merges when they are interesting' 'foo quux'
  % foo quux: we add additional merges when they are interesting
  @  8 "8: change foo" files: foo
  |
  o    7 "7: second merge; change bar" files:
  |\
  | o  6 "6: change foo baz" files: foo
  | |
  o |  5 "5: change bar baz quux" files: quux
  |/
  o    4 "4: first merge; change bar baz" files:
  |\
  | o  3 "3: change bar quux" files: quux
  | |
  o |  2 "2: change foo" files: foo
  |/
  o  1 "1: add bar quux; copy foo to copied" files: quux
  |
  o  0 "0: add foo baz dir/" files: foo
  
  9a7b52012991e4873687192c3e17e61ba3e837a3 644   foo
  bc3eca3f47023a3e70ca0d8cc95a22a6827db19d 644   quux
  $ splitrepo 'partial conversion' 'bar quux' '-r 3'
  % bar quux: partial conversion
  @  1 "3: change bar quux" files: bar quux
  |
  o  0 "1: add bar quux; copy foo to copied" files: bar quux
  
  b79105bedc55102f394e90a789c9c380117c1b4a 644   bar
  db0421cc6b685a458c8d86c7d5c004f94429ea23 644   quux
  $ splitrepo 'complete the partial conversion' 'bar quux'
  % bar quux: complete the partial conversion
  @  4 "7: second merge; change bar" files: bar
  |
  o  3 "5: change bar baz quux" files: bar quux
  |
  o  2 "4: first merge; change bar baz" files: bar
  |
  o  1 "3: change bar quux" files: bar quux
  |
  o  0 "1: add bar quux; copy foo to copied" files: bar quux
  
  9463f52fe115e377cf2878d4fc548117211063f2 644   bar
  bc3eca3f47023a3e70ca0d8cc95a22a6827db19d 644   quux
  $ rm -r foo.repo
  $ splitrepo 'partial conversion' 'foo' '-r 3'
  % foo: partial conversion
  @  0 "0: add foo baz dir/" files: foo
  
  2ed2a3912a0b24502043eae84ee4b279c18b90dd 644   foo
  $ splitrepo 'complete the partial conversion' 'foo'
  % foo: complete the partial conversion
  @  3 "8: change foo" files: foo
  |
  o  2 "6: change foo baz" files: foo
  |
  o  1 "2: change foo" files: foo
  |
  o  0 "0: add foo baz dir/" files: foo
  
  9a7b52012991e4873687192c3e17e61ba3e837a3 644   foo
  $ splitrepo 'copied file; source not included in new repo' copied
  % copied: copied file; source not included in new repo
  @  0 "1: add bar quux; copy foo to copied" files: copied
  
  2ed2a3912a0b24502043eae84ee4b279c18b90dd 644   copied
  $ hg --cwd copied.repo debugrename copied
  copied not renamed
  $ splitrepo 'copied file; source included in new repo' 'foo copied'
  % foo copied: copied file; source included in new repo
  @  4 "8: change foo" files: foo
  |
  o  3 "6: change foo baz" files: foo
  |
  o  2 "2: change foo" files: foo
  |
  o  1 "1: add bar quux; copy foo to copied" files: copied
  |
  o  0 "0: add foo baz dir/" files: foo
  
  7711d36246cc83e61fb29cd6d4ef394c63f1ceaf 644   copied
  9a7b52012991e4873687192c3e17e61ba3e837a3 644   foo
  $ hg --cwd foo-copied.repo debugrename copied
  copied renamed from foo:2ed2a3912a0b24502043eae84ee4b279c18b90dd

verify the top level 'include .' if there is no other includes:

  $ echo "exclude something" > default.fmap
  $ hg convert -q --filemap default.fmap -r1 source dummydest2
  $ hg -R dummydest2 log --template '{rev} {node|short} {desc|firstline}\n'
  1 61e22ca76c3b 1: add bar quux; copy foo to copied
  0 c085cf2ee7fe 0: add foo baz dir/

  $ echo "include somethingelse" >> default.fmap
  $ hg convert -q --filemap default.fmap -r1 source dummydest3
  $ hg -R dummydest3 log --template '{rev} {node|short} {desc|firstline}\n'

  $ echo "include ." >> default.fmap
  $ hg convert -q --filemap default.fmap -r1 source dummydest4
  $ hg -R dummydest4 log --template '{rev} {node|short} {desc|firstline}\n'
  1 61e22ca76c3b 1: add bar quux; copy foo to copied
  0 c085cf2ee7fe 0: add foo baz dir/

ensure that the filemap contains duplicated slashes (issue3612)

  $ cat > renames.fmap <<EOF
  > include dir
  > exclude dir/file2
  > rename dir dir2//dir3
  > include foo
  > include copied
  > rename foo foo2/
  > rename copied ./copied2
  > exclude dir/subdir
  > include dir/subdir/file3
  > EOF
  $ rm source/.hg/store/data/dir/file3.i
  $ rm source/.hg/store/data/dir/file4.i
  $ hg -q convert --filemap renames.fmap --datesort source dummydest
  abort: data/dir/file3.i@e96dce0bc6a2: no match found!
  [255]
  $ hg -q convert --filemap renames.fmap --datesort --config convert.hg.ignoreerrors=1 source renames.repo
  ignoring: data/dir/file3.i@e96dce0bc6a2: no match found
  ignoring: data/dir/file4.i@6edd55f559cd: no match found
  $ hg up -q -R renames.repo
  $ glog -R renames.repo
  @  4 "8: change foo" files: foo2
  |
  o  3 "6: change foo baz" files: foo2
  |
  o  2 "2: change foo" files: foo2
  |
  o  1 "1: add bar quux; copy foo to copied" files: copied2
  |
  o  0 "0: add foo baz dir/" files: dir2/dir3/file dir2/dir3/subdir/file3 foo2
  
  $ hg -R renames.repo verify
  checking changesets
  checking manifests
  crosschecking files in changesets and manifests
  checking files
  4 files, 5 changesets, 7 total revisions

  $ hg -R renames.repo manifest --debug
  d43feacba7a4f1f2080dde4a4b985bd8a0236d46 644   copied2
  3e20847584beff41d7cd16136b7331ab3d754be0 644   dir2/dir3/file
  5fe139720576e18e34bcc9f79174db8897c8afe9 644   dir2/dir3/subdir/file3
  9a7b52012991e4873687192c3e17e61ba3e837a3 644   foo2
  $ hg --cwd renames.repo debugrename copied2
  copied2 renamed from foo2:2ed2a3912a0b24502043eae84ee4b279c18b90dd

copied:

  $ hg --cwd source cat copied
  foo

copied2:

  $ hg --cwd renames.repo cat copied2
  foo

filemap errors

  $ cat > errors.fmap <<EOF
  > include dir/ # beware that comments changes error line numbers!
  > exclude /dir
  > rename dir//dir /dir//dir/ "out of sync"
  > include
  > EOF
  $ hg -q convert --filemap errors.fmap source errors.repo
  errors.fmap:3: superfluous / in include '/dir'
  errors.fmap:3: superfluous / in rename '/dir'
  errors.fmap:4: unknown directive 'out of sync'
  errors.fmap:5: path to exclude is missing
  abort: errors in filemap
  [255]

test branch closing revision pruning if branch is pruned

  $ hg init branchpruning
  $ cd branchpruning
  $ hg branch foo
  marked working directory as branch foo
  (branches are permanent and global, did you want a bookmark?)
  $ echo a > a
  $ hg ci -Am adda
  adding a
  $ hg ci --close-branch -m closefoo
  $ hg up 0
  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg branch empty
  marked working directory as branch empty
  (branches are permanent and global, did you want a bookmark?)
  $ hg ci -m emptybranch
  $ hg ci --close-branch -m closeempty
  $ hg up 0
  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg branch default
  marked working directory as branch default
  (branches are permanent and global, did you want a bookmark?)
  $ echo b > b
  $ hg ci -Am addb
  adding b
  $ hg ci --close-branch -m closedefault
  $ cat > filemap <<EOF
  > include b
  > EOF
  $ cd ..
  $ hg convert branchpruning branchpruning-hg1
  initializing destination branchpruning-hg1 repository
  scanning source...
  sorting...
  converting...
  5 adda
  4 closefoo
  3 emptybranch
  2 closeempty
  1 addb
  0 closedefault
  $ glog -R branchpruning-hg1
  _  5 "closedefault" files:
  |
  o  4 "addb" files: b
  |
  | _  3 "closeempty" files:
  | |
  | o  2 "emptybranch" files:
  |/
  | _  1 "closefoo" files:
  |/
  o  0 "adda" files: a
  

exercise incremental conversion at the same time

  $ hg convert -r0 --filemap branchpruning/filemap branchpruning branchpruning-hg2
  initializing destination branchpruning-hg2 repository
  scanning source...
  sorting...
  converting...
  0 adda
  $ hg convert -r4 --filemap branchpruning/filemap branchpruning branchpruning-hg2
  scanning source...
  sorting...
  converting...
  0 addb
  $ hg convert --filemap branchpruning/filemap branchpruning branchpruning-hg2
  scanning source...
  sorting...
  converting...
  3 closefoo
  2 emptybranch
  1 closeempty
  0 closedefault
  $ glog -R branchpruning-hg2
  _  1 "closedefault" files:
  |
  o  0 "addb" files: b
  

Test rebuilding of map with unknown revisions in shamap - it used to crash

  $ cd branchpruning
  $ hg up -r 2
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
  $ hg merge 4
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ hg ci -m 'merging something'
  $ cd ..
  $ echo "53792d18237d2b64971fa571936869156655338d 6d955580116e82c4b029bd30f321323bae71a7f0" >> branchpruning-hg2/.hg/shamap
  $ hg convert --filemap branchpruning/filemap branchpruning branchpruning-hg2 --debug
  run hg source pre-conversion action
  run hg sink pre-conversion action
  scanning source...
  scanning: 1 revisions
  sorting...
  converting...
  0 merging something
  source: 2503605b178fe50e8fbbb0e77b97939540aa8c87
  converting: 0/1 revisions (0.00%)
  unknown revmap source: 53792d18237d2b64971fa571936869156655338d
  run hg sink post-conversion action
  run hg source post-conversion action


filemap rename undoing revision rename

  $ hg init renameundo
  $ cd renameundo
  $ echo 1 > a
  $ echo 1 > c
  $ hg ci -qAm add
  $ hg mv -q a b/a
  $ hg mv -q c b/c
  $ hg ci -qm rename
  $ echo 2 > b/a
  $ echo 2 > b/c
  $ hg ci -qm modify
  $ cd ..

  $ echo "rename b ." > renameundo.fmap
  $ hg convert --filemap renameundo.fmap renameundo renameundo2
  initializing destination renameundo2 repository
  scanning source...
  sorting...
  converting...
  2 add
  1 rename
  filtering out empty revision
  repository tip rolled back to revision 0 (undo commit)
  0 modify
  $ glog -R renameundo2
  o  1 "modify" files: a c
  |
  o  0 "add" files: a c
  


test merge parents/empty merges pruning

  $ glog()
  > {
  >     hg log -G --template '{rev}:{node|short}@{branch} "{desc}" files: {files}\n' "$@"
  > }

test anonymous branch pruning

  $ hg init anonymousbranch
  $ cd anonymousbranch
  $ echo a > a
  $ echo b > b
  $ hg ci -Am add
  adding a
  adding b
  $ echo a >> a
  $ hg ci -m changea
  $ hg up 0
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ echo b >> b
  $ hg ci -m changeb
  created new head
  $ hg up 1
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg merge
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ hg ci -m merge
  $ cd ..

  $ cat > filemap <<EOF
  > include a
  > EOF
  $ hg convert --filemap filemap anonymousbranch anonymousbranch-hg
  initializing destination anonymousbranch-hg repository
  scanning source...
  sorting...
  converting...
  3 add
  2 changea
  1 changeb
  0 merge
  $ glog -R anonymousbranch
  @    3:c71d5201a498@default "merge" files:
  |\
  | o  2:607eb44b17f9@default "changeb" files: b
  | |
  o |  1:1f60ea617824@default "changea" files: a
  |/
  o  0:0146e6129113@default "add" files: a b
  
  $ glog -R anonymousbranch-hg
  o  1:cda818e7219b@default "changea" files: a
  |
  o  0:c334dc3be0da@default "add" files: a
  
  $ cat anonymousbranch-hg/.hg/shamap
  0146e6129113dba9ac90207cfdf2d7ed35257ae5 c334dc3be0daa2a4e9ce4d2e2bdcba40c09d4916
  1f60ea61782421edf8d051ff4fcb61b330f26a4a cda818e7219b5f7f3fb9f49780054ed6a1905ec3
  607eb44b17f9348cd5cbd26e16af87ba77b0b037 c334dc3be0daa2a4e9ce4d2e2bdcba40c09d4916
  c71d5201a498b2658d105a6bf69d7a0df2649aea cda818e7219b5f7f3fb9f49780054ed6a1905ec3

  $ cat > filemap <<EOF
  > include b
  > EOF
  $ hg convert --filemap filemap anonymousbranch anonymousbranch-hg2
  initializing destination anonymousbranch-hg2 repository
  scanning source...
  sorting...
  converting...
  3 add
  2 changea
  1 changeb
  0 merge
  $ glog -R anonymousbranch
  @    3:c71d5201a498@default "merge" files:
  |\
  | o  2:607eb44b17f9@default "changeb" files: b
  | |
  o |  1:1f60ea617824@default "changea" files: a
  |/
  o  0:0146e6129113@default "add" files: a b
  
  $ glog -R anonymousbranch-hg2
  o  1:62dd350b0df6@default "changeb" files: b
  |
  o  0:4b9ced861657@default "add" files: b
  
  $ cat anonymousbranch-hg2/.hg/shamap
  0146e6129113dba9ac90207cfdf2d7ed35257ae5 4b9ced86165703791653059a1db6ed864630a523
  1f60ea61782421edf8d051ff4fcb61b330f26a4a 4b9ced86165703791653059a1db6ed864630a523
  607eb44b17f9348cd5cbd26e16af87ba77b0b037 62dd350b0df695f7d2c82a02e0499b16fd790f22
  c71d5201a498b2658d105a6bf69d7a0df2649aea 62dd350b0df695f7d2c82a02e0499b16fd790f22

test named branch pruning

  $ hg init namedbranch
  $ cd namedbranch
  $ echo a > a
  $ echo b > b
  $ hg ci -Am add
  adding a
  adding b
  $ echo a >> a
  $ hg ci -m changea
  $ hg up 0
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg branch foo
  marked working directory as branch foo
  (branches are permanent and global, did you want a bookmark?)
  $ echo b >> b
  $ hg ci -m changeb
  $ hg up default
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg merge foo
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ hg ci -m merge
  $ cd ..

  $ cat > filemap <<EOF
  > include a
  > EOF
  $ hg convert --filemap filemap namedbranch namedbranch-hg
  initializing destination namedbranch-hg repository
  scanning source...
  sorting...
  converting...
  3 add
  2 changea
  1 changeb
  0 merge
  $ glog -R namedbranch
  @    3:73899bcbe45c@default "merge" files:
  |\
  | o  2:8097982d19fc@foo "changeb" files: b
  | |
  o |  1:1f60ea617824@default "changea" files: a
  |/
  o  0:0146e6129113@default "add" files: a b
  
  $ glog -R namedbranch-hg
  o  1:cda818e7219b@default "changea" files: a
  |
  o  0:c334dc3be0da@default "add" files: a
  

  $ cd namedbranch
  $ hg --config extensions.mq= strip tip
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  saved backup bundle to $TESTTMP/namedbranch/.hg/strip-backup/73899bcbe45c-92adf160-backup.hg (glob)
  $ hg up foo
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg merge default
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ hg ci -m merge
  $ cd ..

  $ hg convert --filemap filemap namedbranch namedbranch-hg2
  initializing destination namedbranch-hg2 repository
  scanning source...
  sorting...
  converting...
  3 add
  2 changea
  1 changeb
  0 merge
  $ glog -R namedbranch
  @    3:e1959de76e1b@foo "merge" files:
  |\
  | o  2:8097982d19fc@foo "changeb" files: b
  | |
  o |  1:1f60ea617824@default "changea" files: a
  |/
  o  0:0146e6129113@default "add" files: a b
  
  $ glog -R namedbranch-hg2
  o    2:dcf314454667@foo "merge" files:
  |\
  | o  1:cda818e7219b@default "changea" files: a
  |/
  o  0:c334dc3be0da@default "add" files: a