view tests/test-encoding-align.t @ 34824:e2ad93bcc084

revlog: introduce an experimental flag to slice chunks reads when too sparse

Delta chains can become quite sparse if there is a lot of unrelated data between
relevant pieces. Right now, revlog always reads all the necessary data for the
delta chain in one single read. This can lead to a lot of unrelated data to be
read (see issue5482 for more details).
One can use the `experimental.maxdeltachainspan` option with a large value
(or -1) to easily produce a very sparse delta chain.

This change introduces the ability to slice the chunks retrieval into  multiple
reads, skipping large sections of unrelated data. Preliminary testing shows
interesting results. For example the peak memory consumption to read a manifest
on a large repository is reduced from 600MB to 250MB (200MB without
maxdeltachainspan). However, the slicing itself and the multiple reads can have
an negative impact on performance. This is why the new feature is hidden behind
an experimental flag.

Future changesets will add various parameters to control the slicing heuristics.
We hope to experiment a wide variety of repositories during 4.4 and hopefully
turn the feature on by default in 4.5.
As a first try, the algorithm itself is prone to deep changes. However, we wish
to define APIs and have a baseline to work on.

Test alignment of multibyte characters

  $ HGENCODING=utf-8
  $ export HGENCODING
  $ hg init t
  $ cd t
  $ $PYTHON << EOF
  > # (byte, width) = (6, 4)
  > s = "\xe7\x9f\xad\xe5\x90\x8d"
  > # (byte, width) = (7, 7): odd width is good for alignment test
  > m = "MIDDLE_"
  > # (byte, width) = (18, 12)
  > l = "\xe9\x95\xb7\xe3\x81\x84\xe9\x95\xb7\xe3\x81\x84\xe5\x90\x8d\xe5\x89\x8d"
  > f = file('s', 'w'); f.write(s); f.close()
  > f = file('m', 'w'); f.write(m); f.close()
  > f = file('l', 'w'); f.write(l); f.close()
  > # instant extension to show list of options
  > f = file('showoptlist.py', 'w'); f.write("""# encoding: utf-8
  > from mercurial import registrar
  > cmdtable = {}
  > command = registrar.command(cmdtable)
  > 
  > @command(b'showoptlist',
  >     [('s', 'opt1', '', 'short width'  + ' %(s)s' * 8, '%(s)s'),
  >     ('m', 'opt2', '', 'middle width' + ' %(m)s' * 8, '%(m)s'),
  >     ('l', 'opt3', '', 'long width'   + ' %(l)s' * 8, '%(l)s')],
  >     '')
  > def showoptlist(ui, repo, *pats, **opts):
  >     '''dummy command to show option descriptions'''
  >     return 0
  > """ % globals())
  > f.close()
  > EOF
  $ S=`cat s`
  $ M=`cat m`
  $ L=`cat l`

alignment of option descriptions in help

  $ cat <<EOF > .hg/hgrc
  > [extensions]
  > ja_ext = `pwd`/showoptlist.py
  > EOF

check alignment of option descriptions in help

  $ hg help showoptlist
  hg showoptlist
  
  dummy command to show option descriptions
  
  options:
  
   -s --opt1 \xe7\x9f\xad\xe5\x90\x8d         short width \xe7\x9f\xad\xe5\x90\x8d \xe7\x9f\xad\xe5\x90\x8d \xe7\x9f\xad\xe5\x90\x8d \xe7\x9f\xad\xe5\x90\x8d \xe7\x9f\xad\xe5\x90\x8d \xe7\x9f\xad\xe5\x90\x8d \xe7\x9f\xad\xe5\x90\x8d \xe7\x9f\xad\xe5\x90\x8d (esc)
   -m --opt2 MIDDLE_      middle width MIDDLE_ MIDDLE_ MIDDLE_ MIDDLE_ MIDDLE_
                          MIDDLE_ MIDDLE_ MIDDLE_
   -l --opt3 \xe9\x95\xb7\xe3\x81\x84\xe9\x95\xb7\xe3\x81\x84\xe5\x90\x8d\xe5\x89\x8d long width \xe9\x95\xb7\xe3\x81\x84\xe9\x95\xb7\xe3\x81\x84\xe5\x90\x8d\xe5\x89\x8d \xe9\x95\xb7\xe3\x81\x84\xe9\x95\xb7\xe3\x81\x84\xe5\x90\x8d\xe5\x89\x8d \xe9\x95\xb7\xe3\x81\x84\xe9\x95\xb7\xe3\x81\x84\xe5\x90\x8d\xe5\x89\x8d (esc)
                          \xe9\x95\xb7\xe3\x81\x84\xe9\x95\xb7\xe3\x81\x84\xe5\x90\x8d\xe5\x89\x8d \xe9\x95\xb7\xe3\x81\x84\xe9\x95\xb7\xe3\x81\x84\xe5\x90\x8d\xe5\x89\x8d \xe9\x95\xb7\xe3\x81\x84\xe9\x95\xb7\xe3\x81\x84\xe5\x90\x8d\xe5\x89\x8d \xe9\x95\xb7\xe3\x81\x84\xe9\x95\xb7\xe3\x81\x84\xe5\x90\x8d\xe5\x89\x8d (esc)
                          \xe9\x95\xb7\xe3\x81\x84\xe9\x95\xb7\xe3\x81\x84\xe5\x90\x8d\xe5\x89\x8d (esc)
  
  (some details hidden, use --verbose to show complete help)


  $ rm -f s; touch s
  $ rm -f m; touch m
  $ rm -f l; touch l

add files

  $ cp s $S
  $ hg add $S
  $ cp m $M
  $ hg add $M
  $ cp l $L
  $ hg add $L

commit(1)

  $ echo 'first line(1)' >> s; cp s $S
  $ echo 'first line(2)' >> m; cp m $M
  $ echo 'first line(3)' >> l; cp l $L
  $ hg commit -m 'first commit' -u $S

commit(2)

  $ echo 'second line(1)' >> s; cp s $S
  $ echo 'second line(2)' >> m; cp m $M
  $ echo 'second line(3)' >> l; cp l $L
  $ hg commit -m 'second commit' -u $M

commit(3)

  $ echo 'third line(1)' >> s; cp s $S
  $ echo 'third line(2)' >> m; cp m $M
  $ echo 'third line(3)' >> l; cp l $L
  $ hg commit -m 'third commit' -u $L

check alignment of user names in annotate

  $ hg annotate -u $M
          \xe7\x9f\xad\xe5\x90\x8d: first line(2) (esc)
       MIDDLE_: second line(2)
  \xe9\x95\xb7\xe3\x81\x84\xe9\x95\xb7\xe3\x81\x84\xe5\x90\x8d\xe5\x89\x8d: third line(2) (esc)

check alignment of filenames in diffstat

  $ hg diff -c tip --stat
   MIDDLE_      |  1 +
   \xe7\x9f\xad\xe5\x90\x8d         |  1 + (esc)
   \xe9\x95\xb7\xe3\x81\x84\xe9\x95\xb7\xe3\x81\x84\xe5\x90\x8d\xe5\x89\x8d |  1 + (esc)
   3 files changed, 3 insertions(+), 0 deletions(-)

add branches/tags

  $ hg branch $S
  marked working directory as branch \xe7\x9f\xad\xe5\x90\x8d (esc)
  (branches are permanent and global, did you want a bookmark?)
  $ hg tag $S
  $ hg book -f $S
  $ hg branch $M
  marked working directory as branch MIDDLE_
  $ hg tag $M
  $ hg book -f $M
  $ hg branch $L
  marked working directory as branch \xe9\x95\xb7\xe3\x81\x84\xe9\x95\xb7\xe3\x81\x84\xe5\x90\x8d\xe5\x89\x8d (esc)
  $ hg tag $L
  $ hg book -f $L

check alignment of branches

  $ hg branches
  \xe9\x95\xb7\xe3\x81\x84\xe9\x95\xb7\xe3\x81\x84\xe5\x90\x8d\xe5\x89\x8d                   5:d745ff46155b (esc)
  MIDDLE_                        4:9259be597f19 (inactive)
  \xe7\x9f\xad\xe5\x90\x8d                           3:b06c5b6def9e (inactive) (esc)
  default                        2:64a70663cee8 (inactive)

check alignment of tags

  $ hg tags
  tip                                5:d745ff46155b
  \xe9\x95\xb7\xe3\x81\x84\xe9\x95\xb7\xe3\x81\x84\xe5\x90\x8d\xe5\x89\x8d                       4:9259be597f19 (esc)
  MIDDLE_                            3:b06c5b6def9e
  \xe7\x9f\xad\xe5\x90\x8d                               2:64a70663cee8 (esc)

check alignment of bookmarks

  $ hg book
     MIDDLE_                   5:d745ff46155b
     \xe7\x9f\xad\xe5\x90\x8d                      4:9259be597f19 (esc)
   * \xe9\x95\xb7\xe3\x81\x84\xe9\x95\xb7\xe3\x81\x84\xe5\x90\x8d\xe5\x89\x8d              5:d745ff46155b (esc)