tests/test-sparse-revlog.t

snapshot: also consider the snapshot chain of one unrelated revision

To maximize the chance of good delta chain reuse, we inject an unrelated delta
chain into our search. To do so, we search for the highest revision unrelated
to the parents of the current revision and use its snapshot chain too.

Adding this extra snapshot into the mix can have a performance impact. We'll
deal with performance impact in a later series.

====================================
Test delta choice with sparse revlog
====================================

Sparse-revlog usually shows the most gain on Manifest. However, it is simpler
to general an appropriate file, so we test with a single file instead. The
goal is to observe intermediate snapshot being created.

We need a large enough file. Part of the content needs to be replaced
repeatedly while some of it changes rarely.

  $ bundlepath="$TESTDIR/artifacts/cache/big-file-churn.hg"

  $ expectedhash=`cat "$bundlepath".md5`
  $ if [ ! -f "$bundlepath" ]; then
  >     echo 'skipped: missing artifact, run "'"$TESTDIR"'/artifacts/scripts/generate-churning-bundle.py"'
  >     exit 80
  > fi
  $ currenthash=`f -M "$bundlepath" | cut -d = -f 2`
  $ if [ "$currenthash" != "$expectedhash" ]; then
  >     echo 'skipped: outdated artifact, md5 "'"$currenthash"'" expected "'"$expectedhash"'" run "'"$TESTDIR"'/artifacts/scripts/generate-churning-bundle.py"'
  >     exit 80
  > fi

  $ cat >> $HGRCPATH << EOF
  > [format]
  > sparse-revlog = yes
  > [storage]
  > revlog.optimize-delta-parent-choice = yes
  > EOF
  $ hg init sparse-repo
  $ cd sparse-repo
  $ hg unbundle $bundlepath
  adding changesets
  adding manifests
  adding file changes
  added 5001 changesets with 5001 changes to 1 files (+89 heads)
  new changesets 9706f5af64f4:d9032adc8114 (5001 drafts)
  (run 'hg heads' to see heads, 'hg merge' to merge)
  $ hg up
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  updated to "d9032adc8114: commit #5000"
  89 other heads for branch "default"

  $ hg log --stat -r 0:3
  changeset:   0:9706f5af64f4
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     initial commit
  
   SPARSE-REVLOG-TEST-FILE |  10500 ++++++++++++++++++++++++++++++++++++++++++++++
   1 files changed, 10500 insertions(+), 0 deletions(-)
  
  changeset:   1:724907deaa5e
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     commit #1
  
   SPARSE-REVLOG-TEST-FILE |  1068 +++++++++++++++++++++++-----------------------
   1 files changed, 534 insertions(+), 534 deletions(-)
  
  changeset:   2:62c41bce3e5d
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     commit #2
  
   SPARSE-REVLOG-TEST-FILE |  1068 +++++++++++++++++++++++-----------------------
   1 files changed, 534 insertions(+), 534 deletions(-)
  
  changeset:   3:348a9cbd6959
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     commit #3
  
   SPARSE-REVLOG-TEST-FILE |  1068 +++++++++++++++++++++++-----------------------
   1 files changed, 534 insertions(+), 534 deletions(-)
  

  $ f -s .hg/store/data/*.d
  .hg/store/data/_s_p_a_r_s_e-_r_e_v_l_o_g-_t_e_s_t-_f_i_l_e.d: size=59230936
  $ hg debugrevlog *
  format : 1
  flags  : generaldelta
  
  revisions     :     5001
      merges    :      625 (12.50%)
      normal    :     4376 (87.50%)
  revisions     :     5001
      empty     :        0 ( 0.00%)
                     text  :        0 (100.00%)
                     delta :        0 (100.00%)
      snapshot  :      176 ( 3.52%)
        lvl-0   :              3 ( 0.06%)
        lvl-1   :             17 ( 0.34%)
        lvl-2   :             45 ( 0.90%)
        lvl-3   :             56 ( 1.12%)
        lvl-4   :             55 ( 1.10%)
      deltas    :     4825 (96.48%)
  revision size : 59230936
      snapshot  :  5770371 ( 9.74%)
        lvl-0   :         602962 ( 1.02%)
        lvl-1   :        1534153 ( 2.59%)
        lvl-2   :        1604445 ( 2.71%)
        lvl-3   :        1218174 ( 2.06%)
        lvl-4   :         810637 ( 1.37%)
      deltas    : 53460565 (90.26%)
  
  chunks        :     5001
      0x78 (x)  :     5001 (100.00%)
  chunks size   : 59230936
      0x78 (x)  : 59230936 (100.00%)
  
  avg chain length  :       17
  max chain length  :       45
  max chain reach   : 25326012
  compression ratio :       29
  
  uncompressed data size (min/max/avg) : 346468 / 346472 / 346471
  full revision size (min/max/avg)     : 200897 / 201050 / 200987
  inter-snapshot size (min/max/avg)    : 11598 / 171990 / 29869
      level-1   (min/max/avg)          : 14037 / 171990 / 90244
      level-2   (min/max/avg)          : 11632 / 84456 / 35654
      level-3   (min/max/avg)          : 11598 / 41486 / 21753
      level-4   (min/max/avg)          : 11618 / 19913 / 14738
  delta size (min/max/avg)             : 10649 / 105209 / 11079
  
  deltas against prev  : 4156 (86.13%)
      where prev = p1  : 4120     (99.13%)
      where prev = p2  :    0     ( 0.00%)
      other            :   36     ( 0.87%)
  deltas against p1    :  646 (13.39%)
  deltas against p2    :   23 ( 0.48%)
  deltas against other :    0 ( 0.00%)