diff -r 966950954fda -r 4ca7a67c94c8 tests/test-sparse-revlog.t
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/tests/test-sparse-revlog.t	Mon Sep 10 09:08:24 2018 -0700
@@ -0,0 +1,121 @@
+====================================
+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     echo 'skipped: outdated artifact, md5 "'"$currenthash"'" expected "'"$expectedhash"'" run "'"$TESTDIR"'/artifacts/scripts/generate-churning-bundle.py"'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=74365490
+  $ 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  :      101 ( 2.02%)
+        lvl-0   :            101 ( 2.02%)
+      deltas    :     4900 (97.98%)
+  revision size : 74365490
+      snapshot  : 20307865 (27.31%)
+        lvl-0   :       20307865 (27.31%)
+      deltas    : 54057625 (72.69%)
+  
+  chunks        :     5001
+      0x78 (x)  :     5001 (100.00%)
+  chunks size   : 74365490
+      0x78 (x)  : 74365490 (100.00%)
+  
+  avg chain length  :       23
+  max chain length  :       45
+  max chain reach   : 11039464
+  compression ratio :       23
+  
+  uncompressed data size (min/max/avg) : 346468 / 346472 / 346471
+  full revision size (min/max/avg)     : 200927 / 201202 / 201067
+  inter-snapshot size (min/max/avg)    : 0 / 0 / 0
+  delta size (min/max/avg)             : 10649 / 103898 / 11032
+  
+  deltas against prev  : 4231 (86.35%)
+      where prev = p1  : 4172     (98.61%)
+      where prev = p2  :    0     ( 0.00%)
+      other            :   59     ( 1.39%)
+  deltas against p1    :  651 (13.29%)
+  deltas against p2    :   18 ( 0.37%)
+  deltas against other :    0 ( 0.00%)