annotate tests/test-remotefilelog-repack.t @ 40495:3a333a582d7b

remotefilelog: import pruned-down remotefilelog extension from hg-experimental

This is remotefilelog as of my recent patches for compatibility with
current tip of hg, minus support for old versions of Mercurial and
some FB-specific features like their treemanifest extension and
fetching linkrev data from a patched phabricator. The file extutil.py
moved from hgext3rd to remotefilelog.

This is not yet ready to be landed, consider it a preview for
now. Planned changes include:

 * replace lz4 with zstd
 * rename some capabilities, requirements and wireproto commands to mark
   them as experimental
 * consolidate bits of shallowutil with related functions (eg readfile)

I'm certainly open to other (small) changes, but my rough mission is
to land this largely as-is so we can use it as a model of the
functionality we need going forward for lazy-fetching of file contents
from a server.

# no-check-commit because of a few foo_bar functions

Differential Revision: https://phab.mercurial-scm.org/D4782

  $ PYTHONPATH=$TESTDIR/..:$PYTHONPATH
  $ export PYTHONPATH

  $ . "$TESTDIR/remotefilelog-library.sh"

  $ hginit master
  $ cd master
  $ cat >> .hg/hgrc <<EOF
  > [remotefilelog]
  > server=True
  > serverexpiration=-1
  > EOF
  $ echo x > x
  $ hg commit -qAm x
  $ echo x >> x
  $ hg commit -qAm x2
  $ cd ..

  $ hgcloneshallow ssh://user@dummy/master shallow -q
  1 files fetched over 1 fetches - (1 misses, 0.00% hit ratio) over *s (glob)

# Set the prefetchdays config to zero so that all commits are prefetched
# no matter what their creation date is.
  $ cd shallow
  $ cat >> .hg/hgrc <<EOF
  > [remotefilelog]
  > prefetchdays=0
  > EOF
  $ cd ..

# Test that repack cleans up the old files and creates new packs

  $ cd shallow
  $ find $CACHEDIR | sort
  $TESTTMP/hgcache
  $TESTTMP/hgcache/master
  $TESTTMP/hgcache/master/11
  $TESTTMP/hgcache/master/11/f6ad8ec52a2984abaafd7c3b516503785c2072
  $TESTTMP/hgcache/master/11/f6ad8ec52a2984abaafd7c3b516503785c2072/aee31534993a501858fb6dd96a065671922e7d51
  $TESTTMP/hgcache/repos

  $ hg repack

  $ find $CACHEDIR | sort
  $TESTTMP/hgcache
  $TESTTMP/hgcache/master
  $TESTTMP/hgcache/master/packs
  $TESTTMP/hgcache/master/packs/276d308429d0303762befa376788300f0310f90e.histidx
  $TESTTMP/hgcache/master/packs/276d308429d0303762befa376788300f0310f90e.histpack
  $TESTTMP/hgcache/master/packs/8e25dec685d5e0bb1f1b39df3acebda0e0d75c6e.dataidx
  $TESTTMP/hgcache/master/packs/8e25dec685d5e0bb1f1b39df3acebda0e0d75c6e.datapack
  $TESTTMP/hgcache/master/packs/repacklock
  $TESTTMP/hgcache/repos

# Test that the packs are readonly
  $ ls_l $CACHEDIR/master/packs
  -r--r--r--    1145 276d308429d0303762befa376788300f0310f90e.histidx
  -r--r--r--     172 276d308429d0303762befa376788300f0310f90e.histpack
  -r--r--r--    1074 8e25dec685d5e0bb1f1b39df3acebda0e0d75c6e.dataidx
  -r--r--r--      69 8e25dec685d5e0bb1f1b39df3acebda0e0d75c6e.datapack
  -rw-r--r--       0 repacklock

# Test that the data in the new packs is accessible
  $ hg cat -r . x
  x
  x

# Test that adding new data and repacking it results in the loose data and the
# old packs being combined.

  $ cd ../master
  $ echo x >> x
  $ hg commit -m x3
  $ cd ../shallow
  $ hg pull -q
  $ hg up -q tip
  1 files fetched over 1 fetches - (1 misses, 0.00% hit ratio) over * (glob)

  $ find $CACHEDIR -type f | sort
  $TESTTMP/hgcache/master/11/f6ad8ec52a2984abaafd7c3b516503785c2072/d4a3ed9310e5bd9887e3bf779da5077efab28216
  $TESTTMP/hgcache/master/packs/276d308429d0303762befa376788300f0310f90e.histidx
  $TESTTMP/hgcache/master/packs/276d308429d0303762befa376788300f0310f90e.histpack
  $TESTTMP/hgcache/master/packs/8e25dec685d5e0bb1f1b39df3acebda0e0d75c6e.dataidx
  $TESTTMP/hgcache/master/packs/8e25dec685d5e0bb1f1b39df3acebda0e0d75c6e.datapack
  $TESTTMP/hgcache/master/packs/repacklock
  $TESTTMP/hgcache/repos

# First assert that with --packsonly, the loose object will be ignored:

  $ hg repack --packsonly

  $ find $CACHEDIR -type f | sort
  $TESTTMP/hgcache/master/11/f6ad8ec52a2984abaafd7c3b516503785c2072/d4a3ed9310e5bd9887e3bf779da5077efab28216
  $TESTTMP/hgcache/master/packs/276d308429d0303762befa376788300f0310f90e.histidx
  $TESTTMP/hgcache/master/packs/276d308429d0303762befa376788300f0310f90e.histpack
  $TESTTMP/hgcache/master/packs/8e25dec685d5e0bb1f1b39df3acebda0e0d75c6e.dataidx
  $TESTTMP/hgcache/master/packs/8e25dec685d5e0bb1f1b39df3acebda0e0d75c6e.datapack
  $TESTTMP/hgcache/master/packs/repacklock
  $TESTTMP/hgcache/repos

  $ hg repack --traceback

  $ find $CACHEDIR -type f | sort
  $TESTTMP/hgcache/master/packs/077e7ce5dfe862dc40cc8f3c9742d96a056865f2.histidx
  $TESTTMP/hgcache/master/packs/077e7ce5dfe862dc40cc8f3c9742d96a056865f2.histpack
  $TESTTMP/hgcache/master/packs/935861cae0be6ce41a0d47a529e4d097e9e68a69.dataidx
  $TESTTMP/hgcache/master/packs/935861cae0be6ce41a0d47a529e4d097e9e68a69.datapack
  $TESTTMP/hgcache/master/packs/repacklock
  $TESTTMP/hgcache/repos

# Verify all the file data is still available
  $ hg cat -r . x
  x
  x
  x
  $ hg cat -r '.^' x
  x
  x

# Test that repacking again without new data does not delete the pack files
# and did not change the pack names
  $ hg repack
  $ find $CACHEDIR -type f | sort
  $TESTTMP/hgcache/master/packs/077e7ce5dfe862dc40cc8f3c9742d96a056865f2.histidx
  $TESTTMP/hgcache/master/packs/077e7ce5dfe862dc40cc8f3c9742d96a056865f2.histpack
  $TESTTMP/hgcache/master/packs/935861cae0be6ce41a0d47a529e4d097e9e68a69.dataidx
  $TESTTMP/hgcache/master/packs/935861cae0be6ce41a0d47a529e4d097e9e68a69.datapack
  $TESTTMP/hgcache/master/packs/repacklock
  $TESTTMP/hgcache/repos

# Run two repacks at once
  $ hg repack --config "hooks.prerepack=sleep 3" &
  $ sleep 1
  $ hg repack
  skipping repack - another repack is already running
  $ hg debugwaitonrepack >/dev/null 2>&1

# Run repack in the background
  $ cd ../master
  $ echo x >> x
  $ hg commit -m x4
  $ cd ../shallow
  $ hg pull -q
  $ hg up -q tip
  1 files fetched over 1 fetches - (1 misses, 0.00% hit ratio) over * (glob)
  $ find $CACHEDIR -type f | sort
  $TESTTMP/hgcache/master/11/f6ad8ec52a2984abaafd7c3b516503785c2072/1bb2e6237e035c8f8ef508e281f1ce075bc6db72
  $TESTTMP/hgcache/master/packs/077e7ce5dfe862dc40cc8f3c9742d96a056865f2.histidx
  $TESTTMP/hgcache/master/packs/077e7ce5dfe862dc40cc8f3c9742d96a056865f2.histpack
  $TESTTMP/hgcache/master/packs/935861cae0be6ce41a0d47a529e4d097e9e68a69.dataidx
  $TESTTMP/hgcache/master/packs/935861cae0be6ce41a0d47a529e4d097e9e68a69.datapack
  $TESTTMP/hgcache/master/packs/repacklock
  $TESTTMP/hgcache/repos

  $ hg repack --background
  (running background repack)
  $ sleep 0.5
  $ hg debugwaitonrepack >/dev/null 2>&1
  $ find $CACHEDIR -type f | sort
  $TESTTMP/hgcache/master/packs/094b530486dad4427a0faf6bcbc031571b99ca24.histidx
  $TESTTMP/hgcache/master/packs/094b530486dad4427a0faf6bcbc031571b99ca24.histpack
  $TESTTMP/hgcache/master/packs/8fe685c56f6f7edf550bfcec74eeecc5f3c2ba15.dataidx
  $TESTTMP/hgcache/master/packs/8fe685c56f6f7edf550bfcec74eeecc5f3c2ba15.datapack
  $TESTTMP/hgcache/master/packs/repacklock
  $TESTTMP/hgcache/repos

# Test debug commands

  $ hg debugdatapack $TESTTMP/hgcache/master/packs/*.datapack
  $TESTTMP/hgcache/master/packs/8fe685c56f6f7edf550bfcec74eeecc5f3c2ba15:
  x:
  Node          Delta Base    Delta Length  Blob Size
  1bb2e6237e03  000000000000  8             8
  d4a3ed9310e5  1bb2e6237e03  12            6
  aee31534993a  d4a3ed9310e5  12            4
  
  Total:                      32            18        (77.8% bigger)
  $ hg debugdatapack --long $TESTTMP/hgcache/master/packs/*.datapack
  $TESTTMP/hgcache/master/packs/8fe685c56f6f7edf550bfcec74eeecc5f3c2ba15:
  x:
  Node                                      Delta Base                                Delta Length  Blob Size
  1bb2e6237e035c8f8ef508e281f1ce075bc6db72  0000000000000000000000000000000000000000  8             8
  d4a3ed9310e5bd9887e3bf779da5077efab28216  1bb2e6237e035c8f8ef508e281f1ce075bc6db72  12            6
  aee31534993a501858fb6dd96a065671922e7d51  d4a3ed9310e5bd9887e3bf779da5077efab28216  12            4
  
  Total:                                                                              32            18        (77.8% bigger)
  $ hg debugdatapack $TESTTMP/hgcache/master/packs/*.datapack --node d4a3ed9310e5bd9887e3bf779da5077efab28216
  $TESTTMP/hgcache/master/packs/8fe685c56f6f7edf550bfcec74eeecc5f3c2ba15:
  
  x
  Node                                      Delta Base                                Delta SHA1                                Delta Length
  d4a3ed9310e5bd9887e3bf779da5077efab28216  1bb2e6237e035c8f8ef508e281f1ce075bc6db72  77029ab56e83ea2115dd53ff87483682abe5d7ca  12
  Node                                      Delta Base                                Delta SHA1                                Delta Length
  1bb2e6237e035c8f8ef508e281f1ce075bc6db72  0000000000000000000000000000000000000000  7ca8c71a64f7b56380e77573da2f7a5fdd2ecdb5  8
  $ hg debughistorypack $TESTTMP/hgcache/master/packs/*.histidx
  
  x
  Node          P1 Node       P2 Node       Link Node     Copy From
  1bb2e6237e03  d4a3ed9310e5  000000000000  0b03bbc9e1e7  
  d4a3ed9310e5  aee31534993a  000000000000  421535db10b6  
  aee31534993a  1406e7411862  000000000000  a89d614e2364  
  1406e7411862  000000000000  000000000000  b292c1e3311f  

# Test copy tracing from a pack
  $ cd ../master
  $ hg mv x y
  $ hg commit -m 'move x to y'
  $ cd ../shallow
  $ hg pull -q
  $ hg up -q tip
  1 files fetched over 1 fetches - (1 misses, 0.00% hit ratio) over * (glob)
  $ hg repack
  $ hg log -f y -T '{desc}\n'
  move x to y
  x4
  x3
  x2
  x

# Test copy trace across rename and back
  $ cp -R $TESTTMP/hgcache/master/packs $TESTTMP/backuppacks
  $ cd ../master
  $ hg mv y x
  $ hg commit -m 'move y back to x'
  $ hg revert -r 0 x
  $ mv x y
  $ hg add y
  $ echo >> y
  $ hg revert x
  $ hg commit -m 'add y back without metadata'
  $ cd ../shallow
  $ hg pull -q
  $ hg up -q tip
  2 files fetched over 2 fetches - (2 misses, 0.00% hit ratio) over * (glob)
  $ hg repack
  $ ls $TESTTMP/hgcache/master/packs
  e8fdf7ae22b772dcc291f905b9c6e5f381d28739.dataidx
  e8fdf7ae22b772dcc291f905b9c6e5f381d28739.datapack
  ebbd7411e00456c0eec8d1150a77e2b3ef490f3f.histidx
  ebbd7411e00456c0eec8d1150a77e2b3ef490f3f.histpack
  repacklock
  $ hg debughistorypack $TESTTMP/hgcache/master/packs/*.histidx
  
  x
  Node          P1 Node       P2 Node       Link Node     Copy From
  cd410a44d584  577959738234  000000000000  609547eda446  y
  1bb2e6237e03  d4a3ed9310e5  000000000000  0b03bbc9e1e7  
  d4a3ed9310e5  aee31534993a  000000000000  421535db10b6  
  aee31534993a  1406e7411862  000000000000  a89d614e2364  
  1406e7411862  000000000000  000000000000  b292c1e3311f  
  
  y
  Node          P1 Node       P2 Node       Link Node     Copy From
  577959738234  1bb2e6237e03  000000000000  c7faf2fc439a  x
  21f46f2721e7  000000000000  000000000000  d6868642b790  
  $ hg strip -r '.^'
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved
  saved backup bundle to $TESTTMP/shallow/.hg/strip-backup/609547eda446-b26b56a8-backup.hg (glob)
  $ hg -R ../master strip -r '.^'
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved
  saved backup bundle to $TESTTMP/master/.hg/strip-backup/609547eda446-b26b56a8-backup.hg (glob)

  $ rm -rf $TESTTMP/hgcache/master/packs
  $ cp -R $TESTTMP/backuppacks $TESTTMP/hgcache/master/packs

# Test repacking datapack without history
  $ rm -rf $CACHEDIR/master/packs/*hist*
  $ hg repack
  $ hg debugdatapack $TESTTMP/hgcache/master/packs/*.datapack
  $TESTTMP/hgcache/master/packs/a8d86ff8e1a11a77a85f5fea567f56a757583eda:
  x:
  Node          Delta Base    Delta Length  Blob Size
  1bb2e6237e03  000000000000  8             8
  d4a3ed9310e5  1bb2e6237e03  12            6
  aee31534993a  d4a3ed9310e5  12            4
  
  Total:                      32            18        (77.8% bigger)
  y:
  Node          Delta Base    Delta Length  Blob Size
  577959738234  000000000000  70            8
  
  Total:                      70            8         (775.0% bigger)

  $ hg cat -r ".^" x
  x
  x
  x
  x

Incremental repack
  $ rm -rf $CACHEDIR/master/packs/*
  $ cat >> .hg/hgrc <<EOF
  > [remotefilelog]
  > data.generations=60
  >   150
  > fetchpacks=True
  > EOF

Single pack - repack does nothing
  $ hg prefetch -r 0
  1 files fetched over 1 fetches - (0 misses, 100.00% hit ratio) over * (glob)
  $ ls_l $TESTTMP/hgcache/master/packs/ | grep datapack
  -r--r--r--      59 5b7dec902026f0cddb0ef8acb62f27b5698494d4.datapack
  $ ls_l $TESTTMP/hgcache/master/packs/ | grep histpack
  -r--r--r--      90 c3399b56e035f73c3295276ed098235a08a0ed8c.histpack
  $ hg repack --incremental
  $ ls_l $TESTTMP/hgcache/master/packs/ | grep datapack
  -r--r--r--      59 5b7dec902026f0cddb0ef8acb62f27b5698494d4.datapack
  $ ls_l $TESTTMP/hgcache/master/packs/ | grep histpack
  -r--r--r--      90 c3399b56e035f73c3295276ed098235a08a0ed8c.histpack

3 gen1 packs, 1 gen0 pack - packs 3 gen1 into 1
  $ hg prefetch -r 1
  1 files fetched over 1 fetches - (0 misses, 100.00% hit ratio) over * (glob)
  $ hg prefetch -r 2
  1 files fetched over 1 fetches - (0 misses, 100.00% hit ratio) over * (glob)
  $ hg prefetch -r 3
  1 files fetched over 1 fetches - (0 misses, 100.00% hit ratio) over * (glob)
  $ ls_l $TESTTMP/hgcache/master/packs/ | grep datapack
  -r--r--r--      59 5b7dec902026f0cddb0ef8acb62f27b5698494d4.datapack
  -r--r--r--      65 6c499d21350d79f92fd556b4b7a902569d88e3c9.datapack
  -r--r--r--      61 817d294043bd21a3de01f807721971abe45219ce.datapack
  -r--r--r--      63 ff45add45ab3f59c4f75efc6a087d86c821219d6.datapack
  $ ls_l $TESTTMP/hgcache/master/packs/ | grep histpack
  -r--r--r--     254 077e7ce5dfe862dc40cc8f3c9742d96a056865f2.histpack
  -r--r--r--     336 094b530486dad4427a0faf6bcbc031571b99ca24.histpack
  -r--r--r--     172 276d308429d0303762befa376788300f0310f90e.histpack
  -r--r--r--      90 c3399b56e035f73c3295276ed098235a08a0ed8c.histpack

For the data packs, setting the limit for the repackmaxpacksize to be 64 such
that data pack with size 65 is more than the limit. This effectively ensures
that no generation has 3 packs and therefore, no packs are chosen for the
incremental repacking. As for the history packs, setting repackmaxpacksize to be
0 which should always result in no repacking.
  $ hg repack --incremental --config remotefilelog.data.repackmaxpacksize=64 \
  > --config remotefilelog.history.repackmaxpacksize=0
  $ ls_l $TESTTMP/hgcache/master/packs/ | grep datapack
  -r--r--r--      59 5b7dec902026f0cddb0ef8acb62f27b5698494d4.datapack
  -r--r--r--      65 6c499d21350d79f92fd556b4b7a902569d88e3c9.datapack
  -r--r--r--      61 817d294043bd21a3de01f807721971abe45219ce.datapack
  -r--r--r--      63 ff45add45ab3f59c4f75efc6a087d86c821219d6.datapack
  $ ls_l $TESTTMP/hgcache/master/packs/ | grep histpack
  -r--r--r--     254 077e7ce5dfe862dc40cc8f3c9742d96a056865f2.histpack
  -r--r--r--     336 094b530486dad4427a0faf6bcbc031571b99ca24.histpack
  -r--r--r--     172 276d308429d0303762befa376788300f0310f90e.histpack
  -r--r--r--      90 c3399b56e035f73c3295276ed098235a08a0ed8c.histpack

Setting limit for the repackmaxpacksize to be the size of the biggest pack file
which ensures that it is effectively ignored in the incremental repacking.
  $ hg repack --incremental --config remotefilelog.data.repackmaxpacksize=65 \
  > --config remotefilelog.history.repackmaxpacksize=336
  $ ls_l $TESTTMP/hgcache/master/packs/ | grep datapack
  -r--r--r--      59 5b7dec902026f0cddb0ef8acb62f27b5698494d4.datapack
  -r--r--r--     225 8fe685c56f6f7edf550bfcec74eeecc5f3c2ba15.datapack
  $ ls_l $TESTTMP/hgcache/master/packs/ | grep histpack
  -r--r--r--     336 094b530486dad4427a0faf6bcbc031571b99ca24.histpack

1 gen3 pack, 1 gen0 pack - does nothing
  $ hg repack --incremental
  $ ls_l $TESTTMP/hgcache/master/packs/ | grep datapack
  -r--r--r--      59 5b7dec902026f0cddb0ef8acb62f27b5698494d4.datapack
  -r--r--r--     225 8fe685c56f6f7edf550bfcec74eeecc5f3c2ba15.datapack
  $ ls_l $TESTTMP/hgcache/master/packs/ | grep histpack
  -r--r--r--     336 094b530486dad4427a0faf6bcbc031571b99ca24.histpack

Pull should run background repack
  $ cat >> .hg/hgrc <<EOF
  > [remotefilelog]
  > backgroundrepack=True
  > EOF
  $ clearcache
  $ hg prefetch -r 0
  1 files fetched over 1 fetches - (0 misses, 100.00% hit ratio) over * (glob)
  $ hg prefetch -r 1
  1 files fetched over 1 fetches - (0 misses, 100.00% hit ratio) over * (glob)
  $ hg prefetch -r 2
  1 files fetched over 1 fetches - (0 misses, 100.00% hit ratio) over * (glob)
  $ hg prefetch -r 3
  1 files fetched over 1 fetches - (0 misses, 100.00% hit ratio) over * (glob)
  $ ls_l $TESTTMP/hgcache/master/packs/ | grep datapack
  -r--r--r--      59 5b7dec902026f0cddb0ef8acb62f27b5698494d4.datapack
  -r--r--r--      65 6c499d21350d79f92fd556b4b7a902569d88e3c9.datapack
  -r--r--r--      61 817d294043bd21a3de01f807721971abe45219ce.datapack
  -r--r--r--      63 ff45add45ab3f59c4f75efc6a087d86c821219d6.datapack
  $ ls_l $TESTTMP/hgcache/master/packs/ | grep histpack
  -r--r--r--     254 077e7ce5dfe862dc40cc8f3c9742d96a056865f2.histpack
  -r--r--r--     336 094b530486dad4427a0faf6bcbc031571b99ca24.histpack
  -r--r--r--     172 276d308429d0303762befa376788300f0310f90e.histpack
  -r--r--r--      90 c3399b56e035f73c3295276ed098235a08a0ed8c.histpack

  $ hg pull
  pulling from ssh://user@dummy/master
  searching for changes
  no changes found
  (running background incremental repack)
  $ sleep 0.5
  $ hg debugwaitonrepack >/dev/null 2>&1
  $ ls_l $TESTTMP/hgcache/master/packs/ | grep datapack
  -r--r--r--      59 5b7dec902026f0cddb0ef8acb62f27b5698494d4.datapack
  -r--r--r--     225 8fe685c56f6f7edf550bfcec74eeecc5f3c2ba15.datapack
  $ ls_l $TESTTMP/hgcache/master/packs/ | grep histpack
  -r--r--r--     336 094b530486dad4427a0faf6bcbc031571b99ca24.histpack

Test environment variable resolution
  $ CACHEPATH=$TESTTMP/envcache hg prefetch --config 'remotefilelog.cachepath=$CACHEPATH'
  1 files fetched over 1 fetches - (0 misses, 100.00% hit ratio) over * (glob)
  $ find $TESTTMP/envcache | sort
  $TESTTMP/envcache
  $TESTTMP/envcache/master
  $TESTTMP/envcache/master/packs
  $TESTTMP/envcache/master/packs/54afbfda203716c1aa2636029ccc0df18165129e.dataidx
  $TESTTMP/envcache/master/packs/54afbfda203716c1aa2636029ccc0df18165129e.datapack
  $TESTTMP/envcache/master/packs/dcebd8e8d4d97ee88e40dd8f92d8678c10e1a3ad.histidx
  $TESTTMP/envcache/master/packs/dcebd8e8d4d97ee88e40dd8f92d8678c10e1a3ad.histpack

Test local remotefilelog blob is correct when based on a pack
  $ hg prefetch -r .
  1 files fetched over 1 fetches - (0 misses, 100.00% hit ratio) over * (glob)
  $ echo >> y
  $ hg commit -m y2
  $ hg debugremotefilelog .hg/store/data/95cb0bfd2977c761298d9624e4b4d4c72a39974a/b70860edba4f8242a1d52f2a94679dd23cb76808
  size: 9 bytes
  path: .hg/store/data/95cb0bfd2977c761298d9624e4b4d4c72a39974a/b70860edba4f8242a1d52f2a94679dd23cb76808 
  key: b70860edba4f 
  
          node =>           p1            p2      linknode     copyfrom
  b70860edba4f => 577959738234  000000000000  08d3fbc98c48  
  577959738234 => 1bb2e6237e03  000000000000  c7faf2fc439a  x
  1bb2e6237e03 => d4a3ed9310e5  000000000000  0b03bbc9e1e7  
  d4a3ed9310e5 => aee31534993a  000000000000  421535db10b6  
  aee31534993a => 1406e7411862  000000000000  a89d614e2364  
  1406e7411862 => 000000000000  000000000000  b292c1e3311f  

Test limiting the max delta chain length
  $ hg repack --config packs.maxchainlen=1
  $ hg debugdatapack $TESTTMP/hgcache/master/packs/*.dataidx
  $TESTTMP/hgcache/master/packs/a2731c9a16403457b67337a620931797fce8c821:
  x:
  Node          Delta Base    Delta Length  Blob Size
  1bb2e6237e03  000000000000  8             8
  d4a3ed9310e5  1bb2e6237e03  12            6
  aee31534993a  000000000000  4             4
  1406e7411862  aee31534993a  12            2
  
  Total:                      36            20        (80.0% bigger)
  y:
  Node          Delta Base    Delta Length  Blob Size
  577959738234  000000000000  8             8
  
  Total:                      8             8         (0.0% bigger)

Test huge pack cleanup using different values of packs.maxpacksize:
  $ hg repack --incremental --debug
  $ hg repack --incremental --debug --config packs.maxpacksize=512
  removing oversize packfile $TESTTMP/hgcache/master/packs/a2731c9a16403457b67337a620931797fce8c821.datapack (365 bytes)
  removing oversize packfile $TESTTMP/hgcache/master/packs/a2731c9a16403457b67337a620931797fce8c821.dataidx (1.21 KB)

Do a repack where the new pack reuses a delta from the old pack
  $ clearcache
  $ hg prefetch -r '2::3'
  2 files fetched over 1 fetches - (0 misses, 100.00% hit ratio) over * (glob)
  $ hg repack
  $ hg debugdatapack $CACHEDIR/master/packs/*.datapack
  $TESTTMP/hgcache/master/packs/abf210f6c3aa4dd0ecc7033633ad73591be16c95:
  x:
  Node          Delta Base    Delta Length  Blob Size
  1bb2e6237e03  000000000000  8             8
  d4a3ed9310e5  1bb2e6237e03  12            6
  
  Total:                      20            14        (42.9% bigger)
  $ hg prefetch -r '0::1'
  2 files fetched over 1 fetches - (0 misses, 100.00% hit ratio) over * (glob)
  $ hg repack
  $ hg debugdatapack $CACHEDIR/master/packs/*.datapack
  $TESTTMP/hgcache/master/packs/09b8bf49256b3fc2175977ba97d6402e91a9a604:
  x:
  Node          Delta Base    Delta Length  Blob Size
  1bb2e6237e03  000000000000  8             8
  d4a3ed9310e5  1bb2e6237e03  12            6
  aee31534993a  d4a3ed9310e5  12            4
  1406e7411862  aee31534993a  12            2
  
  Total:                      44            20        (120.0% bigger)