view tests/test-remotefilelog-repack.t @ 46667:93e9f448273c

rhg: Add support for automatic fallback to Python

`rhg` is a command-line application that can do a small subset of what
`hg` can. It is written entirely in Rust, which avoids the cost of starting
a Python interpreter and importing many Python modules.
In a script that runs many `hg` commands, this cost can add up.

However making users decide when to use `rhg` instead of `hg` is
not practical as we want the subset of supported functionality
to grow over time.

Instead we introduce "fallback" behavior where, when `rhg` encounters
something (a sub-command, a repository format, …) that is not implemented
in Rust-only, it does nothing but silently start a subprocess of
Python-based `hg` running the same command.
That way `rhg` becomes a drop-in replacement for `hg` that sometimes
goes faster. Whether Python is used should be an implementation detail
not apparent to users (other than through speed).

A new `fallback` value is added to the previously introduced
`rhg.on-unsupported` configuration key. When in this mode, the new
`rhg.fallback-executable` config is determine what command to use
to run a Python-based `hg`.

The previous `rhg.on-unsupported = abort-silent` configuration was designed
to let a wrapper script call `rhg` and then fall back to `hg` based on the
exit code. This is still available, but having fallback behavior built-in
in rhg might be easier for users instead of leaving that script "as an
exercise for the reader".

Using a subprocess like this is not idea, especially when `rhg` is to be
installed in `$PATH` as `hg`, since the other `hg.py` executable needs
to still be available… somewhere. Eventually this could be replaced
by using PyOxidizer to a have a single executable that embeds a Python
interpreter, but only starts it when needed.

Differential Revision: https://phab.mercurial-scm.org/D10093

#require no-windows

  $ . "$TESTDIR/remotefilelog-library.sh"
  $ cat >> $HGRCPATH <<EOF
  > [devel]
  > remotefilelog.bg-wait=True
  > EOF

  $ hg init 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/1e91b207daf5d7b48f1be9c587d6b5ae654ce78c.histidx
  $TESTTMP/hgcache/master/packs/1e91b207daf5d7b48f1be9c587d6b5ae654ce78c.histpack
  $TESTTMP/hgcache/master/packs/b1e0cfc7f345e408a7825e3081501959488d59ce.dataidx
  $TESTTMP/hgcache/master/packs/b1e0cfc7f345e408a7825e3081501959488d59ce.datapack
  $TESTTMP/hgcache/repos

# Test that the packs are readonly
  $ ls_l $CACHEDIR/master/packs
  -r--r--r--    1145 1e91b207daf5d7b48f1be9c587d6b5ae654ce78c.histidx
  -r--r--r--     172 1e91b207daf5d7b48f1be9c587d6b5ae654ce78c.histpack
  -r--r--r--    1074 b1e0cfc7f345e408a7825e3081501959488d59ce.dataidx
  -r--r--r--      72 b1e0cfc7f345e408a7825e3081501959488d59ce.datapack

# 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/1e91b207daf5d7b48f1be9c587d6b5ae654ce78c.histidx
  $TESTTMP/hgcache/master/packs/1e91b207daf5d7b48f1be9c587d6b5ae654ce78c.histpack
  $TESTTMP/hgcache/master/packs/b1e0cfc7f345e408a7825e3081501959488d59ce.dataidx
  $TESTTMP/hgcache/master/packs/b1e0cfc7f345e408a7825e3081501959488d59ce.datapack
  $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/1e91b207daf5d7b48f1be9c587d6b5ae654ce78c.histidx
  $TESTTMP/hgcache/master/packs/1e91b207daf5d7b48f1be9c587d6b5ae654ce78c.histpack
  $TESTTMP/hgcache/master/packs/b1e0cfc7f345e408a7825e3081501959488d59ce.dataidx
  $TESTTMP/hgcache/master/packs/b1e0cfc7f345e408a7825e3081501959488d59ce.datapack
  $TESTTMP/hgcache/repos

  $ hg repack --traceback

  $ find $CACHEDIR -type f | sort
  $TESTTMP/hgcache/master/packs/78840d69389c7404327f7477e3931c89945c37d1.dataidx
  $TESTTMP/hgcache/master/packs/78840d69389c7404327f7477e3931c89945c37d1.datapack
  $TESTTMP/hgcache/master/packs/8abe7889aae389337d12ebe6085d4ee13854c7c9.histidx
  $TESTTMP/hgcache/master/packs/8abe7889aae389337d12ebe6085d4ee13854c7c9.histpack
  $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/78840d69389c7404327f7477e3931c89945c37d1.dataidx
  $TESTTMP/hgcache/master/packs/78840d69389c7404327f7477e3931c89945c37d1.datapack
  $TESTTMP/hgcache/master/packs/8abe7889aae389337d12ebe6085d4ee13854c7c9.histidx
  $TESTTMP/hgcache/master/packs/8abe7889aae389337d12ebe6085d4ee13854c7c9.histpack
  $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/78840d69389c7404327f7477e3931c89945c37d1.dataidx
  $TESTTMP/hgcache/master/packs/78840d69389c7404327f7477e3931c89945c37d1.datapack
  $TESTTMP/hgcache/master/packs/8abe7889aae389337d12ebe6085d4ee13854c7c9.histidx
  $TESTTMP/hgcache/master/packs/8abe7889aae389337d12ebe6085d4ee13854c7c9.histpack
  $TESTTMP/hgcache/repos

  $ hg repack --background
  (running background repack)
  $ find $CACHEDIR -type f | sort
  $TESTTMP/hgcache/master/packs/39443fa1064182e93d968b5cba292eb5283260d0.dataidx
  $TESTTMP/hgcache/master/packs/39443fa1064182e93d968b5cba292eb5283260d0.datapack
  $TESTTMP/hgcache/master/packs/604552d403a1381749faf656feca0ca265a6d52c.histidx
  $TESTTMP/hgcache/master/packs/604552d403a1381749faf656feca0ca265a6d52c.histpack
  $TESTTMP/hgcache/repos

# Test debug commands

  $ hg debugdatapack $TESTTMP/hgcache/master/packs/*.datapack
  $TESTTMP/hgcache/master/packs/39443fa1064182e93d968b5cba292eb5283260d0:
  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/39443fa1064182e93d968b5cba292eb5283260d0:
  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/39443fa1064182e93d968b5cba292eb5283260d0:
  
  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
  bfd60adb76018bb952e27cd23fc151bf94865d7d.histidx
  bfd60adb76018bb952e27cd23fc151bf94865d7d.histpack
  fb3aa57b22789ebcc45706c352e2d6af099c5816.dataidx
  fb3aa57b22789ebcc45706c352e2d6af099c5816.datapack
  $ 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/922aca43dbbeda4d250565372e8892ec7b08da6a:
  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
  > EOF

Single pack - repack does nothing
  $ hg prefetch -r 0
  1 files fetched over 1 fetches - (1 misses, 0.00% hit ratio) over * (glob)
  $ ls_l $TESTTMP/hgcache/master/packs/ | grep datapack
  [1]
  $ ls_l $TESTTMP/hgcache/master/packs/ | grep histpack
  [1]
  $ hg repack --incremental
  $ ls_l $TESTTMP/hgcache/master/packs/ | grep datapack
  -r--r--r--      70 052643fdcdebbd42d7c180a651a30d46098e6fe1.datapack
  $ ls_l $TESTTMP/hgcache/master/packs/ | grep histpack
  -r--r--r--      90 955a622173324b2d8b53e1147f209f1cf125302e.histpack

3 gen1 packs, 1 gen0 pack - packs 3 gen1 into 1
  $ hg prefetch -r 1
  1 files fetched over 1 fetches - (1 misses, 0.00% hit ratio) over * (glob)
  $ hg prefetch -r 2
  1 files fetched over 1 fetches - (1 misses, 0.00% hit ratio) over * (glob)
  $ hg prefetch -r 38
  abort: unknown revision '38'
  [255]
  $ ls_l $TESTTMP/hgcache/master/packs/ | grep datapack
  -r--r--r--      70 052643fdcdebbd42d7c180a651a30d46098e6fe1.datapack
  $ ls_l $TESTTMP/hgcache/master/packs/ | grep histpack
  -r--r--r--      90 955a622173324b2d8b53e1147f209f1cf125302e.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--      70 052643fdcdebbd42d7c180a651a30d46098e6fe1.datapack
  -r--r--r--     149 78840d69389c7404327f7477e3931c89945c37d1.datapack
  $ ls_l $TESTTMP/hgcache/master/packs/ | grep histpack
  -r--r--r--     254 8abe7889aae389337d12ebe6085d4ee13854c7c9.histpack
  -r--r--r--      90 955a622173324b2d8b53e1147f209f1cf125302e.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--      70 052643fdcdebbd42d7c180a651a30d46098e6fe1.datapack
  -r--r--r--     149 78840d69389c7404327f7477e3931c89945c37d1.datapack
  $ ls_l $TESTTMP/hgcache/master/packs/ | grep histpack
  -r--r--r--     254 8abe7889aae389337d12ebe6085d4ee13854c7c9.histpack
  -r--r--r--      90 955a622173324b2d8b53e1147f209f1cf125302e.histpack

1 gen3 pack, 1 gen0 pack - does nothing
  $ hg repack --incremental
  $ ls_l $TESTTMP/hgcache/master/packs/ | grep datapack
  -r--r--r--      70 052643fdcdebbd42d7c180a651a30d46098e6fe1.datapack
  -r--r--r--     149 78840d69389c7404327f7477e3931c89945c37d1.datapack
  $ ls_l $TESTTMP/hgcache/master/packs/ | grep histpack
  -r--r--r--     254 8abe7889aae389337d12ebe6085d4ee13854c7c9.histpack
  -r--r--r--      90 955a622173324b2d8b53e1147f209f1cf125302e.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 - (1 misses, 0.00% hit ratio) over * (glob)
  $ hg prefetch -r 1
  1 files fetched over 1 fetches - (1 misses, 0.00% hit ratio) over * (glob)
  $ hg prefetch -r 2
  1 files fetched over 1 fetches - (1 misses, 0.00% hit ratio) over * (glob)
  $ hg prefetch -r 3
  1 files fetched over 1 fetches - (1 misses, 0.00% hit ratio) over * (glob)

  $ hg pull
  pulling from ssh://user@dummy/master
  searching for changes
  no changes found
  (running background incremental repack)
  $ ls_l $TESTTMP/hgcache/master/packs/ | grep datapack
  -r--r--r--     303 156a6c1c83aeb69422d7936e0a46ba9bc06a71c0.datapack
  $ ls_l $TESTTMP/hgcache/master/packs/ | grep histpack
  -r--r--r--     336 604552d403a1381749faf656feca0ca265a6d52c.histpack

Test environment variable resolution
  $ CACHEPATH=$TESTTMP/envcache hg prefetch --config 'remotefilelog.cachepath=$CACHEPATH'
  1 files fetched over 1 fetches - (1 misses, 0.00% hit ratio) over * (glob)
  $ find $TESTTMP/envcache | sort
  $TESTTMP/envcache
  $TESTTMP/envcache/master
  $TESTTMP/envcache/master/95
  $TESTTMP/envcache/master/95/cb0bfd2977c761298d9624e4b4d4c72a39974a
  $TESTTMP/envcache/master/95/cb0bfd2977c761298d9624e4b4d4c72a39974a/577959738234a1eb241ed3ed4b22a575833f56e0
  $TESTTMP/envcache/repos

Test local remotefilelog blob is correct when based on a pack
  $ hg prefetch -r .
  1 files fetched over 1 fetches - (1 misses, 0.00% 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/f258af4c033dd5cd32b4dbc42a1efcd8e4c7d909:
  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  70            8
  
  Total:                      70            8         (775.0% 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/f258af4c033dd5cd32b4dbc42a1efcd8e4c7d909.datapack (425 bytes)
  removing oversize packfile $TESTTMP/hgcache/master/packs/f258af4c033dd5cd32b4dbc42a1efcd8e4c7d909.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 - (2 misses, 0.00% hit ratio) over * (glob)
  $ hg repack
  $ hg debugdatapack $CACHEDIR/master/packs/*.datapack
  $TESTTMP/hgcache/master/packs/9ec6b30891bd851320acb7c66b69a2bdf41c8df3:
  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 - (2 misses, 0.00% hit ratio) over * (glob)
  $ hg repack
  $ hg debugdatapack $CACHEDIR/master/packs/*.datapack
  $TESTTMP/hgcache/master/packs/156a6c1c83aeb69422d7936e0a46ba9bc06a71c0:
  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)